Low frequency modulation in high frequency DDS generated signal

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It may not display this or other websites correctly.<br />You should upgrade or use an <a href="https://www.google.com/chrome/" target="_blank" rel="noopener">alternative browser</a>.</div> <div class="p-body-header"> <div class="p-title "> <h1 class="p-title-value">Low frequency modulation in high frequency DDS generated signal</h1> </div> <div class="p-description"> <ul class="listInline listInline--bullet"> <li> <i class="fa--xf fal fa-user" aria-hidden="true" title="Thread starter"></i> <span class="u-srOnly">Thread starter</span> <a href="/members/quant01.691370/" class="username u-concealed" dir="auto" data-user-id="691370" data-xf-init="member-tooltip">Quant01</a> </li> <li> <i class="fa--xf fal fa-clock" aria-hidden="true" title="Start date"></i> <span class="u-srOnly">Start date</span> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/" class="u-concealed"><time class="u-dt" dir="auto" datetime="2024-11-13T11:39:30+0000" data-time="1731497970" data-date-string="Nov 13, 2024" data-time-string="11:39 AM" title="Nov 13, 2024 at 11:39 AM">Nov 13, 2024</time></a> </li> </ul> </div> </div> <div class="p-body-main p-body-main--withSidebar "> <div class="p-body-contentCol"></div> <div class="p-body-sidebarCol"></div> <div class="p-body-content">  <div id='div-gpt-eda_wallpaper'> <script> googletag.cmd.push(function() { googletag.display('div-gpt-eda_wallpaper'); }); </script> </div> <div class="p-body-pageContent"> <div class="block block--messages " data-xf-init="lightbox select-to-quote" data-message-selector=".js-post" data-lb-id="thread-413002"> <div class="block-outer"></div> <div class="block-outer js-threadStatusField"></div> <div class="block-container"> <div class="block-body"> <article class="message message--post js-post js-inlineModContainer " data-author="Quant01" data-content="post-1783855" id="js-post-1783855" > <span class="u-anchorTarget" id="post-1783855"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783855" rel="nofollow" > <time class="u-dt" dir="auto" datetime="2024-11-13T11:39:30+0000" data-time="1731497970" data-date-string="Nov 13, 2024" data-time-string="11:39 AM" title="Nov 13, 2024 at 11:39 AM">Nov 13, 2024</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783855" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1783855/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783855" rel="nofollow"> #1 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" > <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/quant01.691370/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="691370" data-xf-init="member-tooltip" style="background-color: #525214; color: #d1d147"> <span class="avatar-u691370-m" role="img" aria-label="Quant01">Q</span> </a> </div> </div> <div class="message-userDetails"> <h4 class="message-name"><a href="/members/quant01.691370/" class="username " dir="auto" data-user-id="691370" data-xf-init="member-tooltip">Quant01</a></h4> <h5 class="userTitle message-userTitle" dir="auto">Newbie level 5</h5> </div> <img src="/styles/images/ranks/blevel2.gif" alt="Newbie level 5"> <div class="message-userExtras"> <dl class="pairs pairs--justified joinedBlock"> <dt>Joined</dt> <dd>Nov 13, 2024</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed"> <dt>Messages</dt> <dd>9</dd> </dl> <dl class="pairs pairs--justified"> <dt> Helped</dt> <dd>0</dd> </dl> <dl class="pairs pairs--justified"> <dt>Reputation </dt> <dd> <a href="/reputation/authors/quant01.691370" class="fauxBlockLink-linkRow u-concealed">0</a> </dd> </dl> <dl class="pairs pairs--justified"> <dt>Reaction score</dt> <dd>0</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed trophyBlock"> <dt>Trophy points</dt> <dd>1</dd> </dl> <dl class="pairs pairs--justified creditBlock"> <dt title="Activity points">Activity points</dt> <dd> <a href="/activity/" data-xf-click="overlay" class="fauxBlockLink-blockLink u-concealed"> 130 </a> </dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1783855" data-lb-caption-desc="Quant01 · Nov 13, 2024 at 11:39 AM"> <article class="message-body js-selectToQuote"> <div > <div class="bbWrapper">Hi all, <br /> Recently, I posted the following message on another forum and was advised to ask around in a DSP forum :<br /> <br /> "I've been using an arbitrary waveform generator for one of my projects, and specifically, I'm using a DDS option on that AWG (the waveform generator is an M4i6621x8 from Spectrum Instrumentation). Essentially, I'm sending asking the DDS to output a sum of RF sine waves, all of them being on the order of 10s of MHz, with a delta in frequency of at least 1Mhz. However, on the output signal, if I ask for a certain amount of sin waves (usually 5 or more), I start observing a modulation of the amplitude of frequency a few hundred mHz (orders of magnitude away from my input frequencies). The modulation is sinusoidal.<br /> My questions are : why does this happen and how can I remove this feature ? I would expect some MHz beating because of how sum of sine functions work, but definitely not mHz. <br /> Some additional information : <br /> -the frequency resolution of the DDS is about 290 mHz, so this value seems to fit with the observed beating, but I fail to see how this could be related to the issue. <br /> -I didn't notice such beating when using less than 5 frequencies as an input. <br /> -I am using a ZHL-1-2W+ power amplifier at the output of the AWG, which is then connected to an acousto optic deflector (a device that diffracts a laser beam according to input frequencies). The amplitude modulation becomes visible on camera based on the intensity of the diffracted beams."<br /> <br /> If anyone knows how to solve this issue or has any idea, it would be greatly appreciated. <br /> Thanks in advance.</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/reply?quote=1783855" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1783855/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> </div> </article> </div> </div> </div> <div class="block block--messages" data-xf-init="" 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js-inlineModContainer " data-author="KlausST" data-content="post-1783865" id="js-post-1783865" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1783865/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/" /> <span class="u-anchorTarget" id="post-1783865"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783865" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2024-11-13T15:10:46+0000" data-time="1731510646" data-date-string="Nov 13, 2024" data-time-string="3:10 PM" title="Nov 13, 2024 at 3:10 PM" itemprop="datePublished">Nov 13, 2024</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783865" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1783865/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783865" rel="nofollow"> #2 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/klausst.544298/"> <meta itemprop="url" content="https://www.edaboard.com/members/klausst.544298/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/klausst.544298/" class="avatar avatar--m" data-user-id="544298" data-xf-init="member-tooltip"> <img src="/data/avatars/m/544/544298.jpg?1591959018" srcset="/data/avatars/l/544/544298.jpg?1591959018 2x" alt="KlausST" class="avatar-u544298-m" width="96" height="96" loading="lazy" itemprop="image" /> </a> </div> </div> <div class="message-userDetails"> <h4 class="message-name"><a href="/members/klausst.544298/" class="username " dir="auto" data-user-id="544298" data-xf-init="member-tooltip"><span itemprop="name">KlausST</span></a></h4> <h5 class="userTitle message-userTitle" dir="auto" itemprop="jobTitle">Advanced Member level 7</h5> </div> <img src="/styles/images/ranks/hlevel4.gif" alt="Advanced Member level 7"> <div class="message-userExtras"> <dl class="pairs pairs--justified joinedBlock"> <dt>Joined</dt> <dd>Apr 17, 2014</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed"> <dt>Messages</dt> <dd>26,150</dd> </dl> <dl class="pairs pairs--justified"> <dt> Helped</dt> <dd>4,921</dd> </dl> <dl class="pairs pairs--justified"> <dt>Reputation </dt> <dd> <a 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/> <br /> <blockquote data-attributes="member: 691370" data-quote="Quant01" data-source="post: 1783855" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1783855" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1783855">Quant01 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> I ask for a certain amount of sin waves (usually 5 or more), </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>which are in the 10s of MHz.<br /> <br /> So 5 sine waves @ 5MHz .. is just a signal time of 1us.<br /> <br /> But you say:<br /> <blockquote data-attributes="member: 691370" data-quote="Quant01" data-source="post: 1783855" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1783855" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1783855">Quant01 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> I start observing a modulation of the amplitude of frequency a few hundred mHz </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>to see 100mHz .. you need to analyze at least 10 seconds, which means 50.000.000 sinewaves with a frequency of 10MHz.<br /> <br /> **<br /> Where am I wrong?<br /> <br /> Klaus</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" 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class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1783869" data-lb-caption-desc="kaz1 · Nov 13, 2024 at 5:28 PM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper"><blockquote data-attributes="member: 691370" data-quote="Quant01" data-source="post: 1783855" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1783855" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1783855">Quant01 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Hi all,<br /> Recently, I posted the following message on another forum and was advised to ask around in a DSP forum :<br /> <br /> "I've been using an arbitrary waveform generator for one of my projects, and specifically, I'm using a DDS option on that AWG (the waveform generator is an M4i6621x8 from Spectrum Instrumentation). Essentially, I'm sending asking the DDS to output a sum of RF sine waves, all of them being on the order of 10s of MHz, with a delta in frequency of at least 1Mhz. However, on the output signal, if I ask for a certain amount of sin waves (usually 5 or more), I start observing a modulation of the amplitude of frequency a few hundred mHz (orders of magnitude away from my input frequencies). The modulation is sinusoidal.<br /> My questions are : why does this happen and how can I remove this feature ? I would expect some MHz beating because of how sum of sine functions work, but definitely not mHz.<br /> Some additional information :<br /> -the frequency resolution of the DDS is about 290 mHz, so this value seems to fit with the observed beating, but I fail to see how this could be related to the issue.<br /> -I didn't notice such beating when using less than 5 frequencies as an input.<br /> -I am using a ZHL-1-2W+ power amplifier at the output of the AWG, which is then connected to an acousto optic deflector (a device that diffracts a laser beam according to input frequencies). The amplitude modulation becomes visible on camera based on the intensity of the diffracted beams."<br /> <br /> If anyone knows how to solve this issue or has any idea, it would be greatly appreciated.<br /> Thanks in advance. </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>I suggest you try frequencies as multiples of DDS resolution e.g. for 5MHz try 0.29 * 18MHz = 5.22MHz</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/reply?quote=1783869" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1783869/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div class="contentVote js-contentVote " data-xf-init="content-vote" data-content-id="post-1783869"> <meta itemprop="upvoteCount" content="0" /> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--up " data-vote="up"><span class="u-srOnly">Upvote</span></a> <span class="contentVote-score js-voteCount" data-score="0">0</span> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--down " data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="Quant01" data-content="post-1783888" id="js-post-1783888" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1783888/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/" /> <span class="u-anchorTarget" id="post-1783888"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783888" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2024-11-14T06:19:42+0000" data-time="1731565182" data-date-string="Nov 14, 2024" data-time-string="6:19 AM" title="Nov 14, 2024 at 6:19 AM" itemprop="datePublished">Nov 14, 2024</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783888" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1783888/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783888" rel="nofollow"> #4 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/quant01.691370/"> <meta itemprop="url" content="https://www.edaboard.com/members/quant01.691370/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/quant01.691370/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="691370" data-xf-init="member-tooltip" style="background-color: #525214; 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The frequencies that I ask the DDS to output are 50MHz or so. So for instance I could have A*sin(2pi*f1*t)+B*sin(2pi*f2*t) as a requested output, with f1 and f2 being 50MHz and 52MHz. Then on the oscilloscope, I look at the signals overall shape for 20 seconds or so, and when checking this, I can see an amplitude modulation of frequency 100mHz or so (to be specific, something close to 290mHz). Attached is a screenshot of the observed amplitude. Does this clear up the misunderstanding ?<br /> Best regards, <br /> Quant</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> <section class="message-attachments"> <h4 class="block-textHeader">Attachments</h4> <ul class="attachmentList"> <li class="file file--linked"> <a class="u-anchorTarget" id="attachment-195367"></a> <script class="js-extraPhrases" type="application/json"> { "lightbox_close": "Close", "lightbox_next": "Next", "lightbox_previous": "Previous", "lightbox_error": "The requested content cannot be loaded. 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I will definitely try something along those lines. Hopefully I'll be able to extract some interesting information from that test.<br /> Best regards,<br /> Quant</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/reply?quote=1783889" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1783889/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" 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data-lb-caption-desc="FvM · Nov 14, 2024 at 7:27 AM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper">Without knowing the exact combination of generated frequencies, it's impossible to determine if it's regular interference or a generator artefact. You should also consider simple oscilloscope undersampling, does the modulation show with a spectrum analyzer or power meter?</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/reply?quote=1783890" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1783890/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget 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itemid="https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/" /> <span class="u-anchorTarget" id="post-1783893"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783893" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2024-11-14T08:19:28+0000" data-time="1731572368" data-date-string="Nov 14, 2024" data-time-string="8:19 AM" title="Nov 14, 2024 at 8:19 AM" itemprop="datePublished">Nov 14, 2024</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783893" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1783893/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783893" rel="nofollow"> #7 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/klausst.544298/"> <meta itemprop="url" content="https://www.edaboard.com/members/klausst.544298/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/klausst.544298/" class="avatar avatar--m" data-user-id="544298" data-xf-init="member-tooltip"> <img src="/data/avatars/m/544/544298.jpg?1591959018" srcset="/data/avatars/l/544/544298.jpg?1591959018 2x" alt="KlausST" class="avatar-u544298-m" width="96" height="96" loading="lazy" itemprop="image" /> </a> </div> </div> <div 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data-xf-click="attribution" data-content-selector="#post-1783888">Quant01 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Then on the oscilloscope, I look at the signals overall shape for 20 seconds or so, and when checking this, I can see an amplitude modulation of frequency 100mHz or so </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>I agree with FvM ... I assume it is just a measurement artefact.<br /> <br /> Still I don´t know what this means:<br /> <blockquote data-attributes="" data-quote="" data-source="" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> if I ask for a certain amount of sin waves (usually 5 or more) </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote><br /> Klaus</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/reply?quote=1783893" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1783893/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div class="contentVote js-contentVote " data-xf-init="content-vote" data-content-id="post-1783893"> <meta itemprop="upvoteCount" content="0" /> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--up " data-vote="up"><span class="u-srOnly">Upvote</span></a> <span class="contentVote-score js-voteCount" data-score="0">0</span> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--down " data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="Quant01" data-content="post-1783894" id="js-post-1783894" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1783894/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/" /> <span class="u-anchorTarget" id="post-1783894"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783894" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2024-11-14T08:32:55+0000" data-time="1731573175" data-date-string="Nov 14, 2024" data-time-string="8:32 AM" title="Nov 14, 2024 at 8:32 AM" itemprop="datePublished">Nov 14, 2024</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783894" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1783894/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783894" rel="nofollow"> #8 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/quant01.691370/"> <meta itemprop="url" content="https://www.edaboard.com/members/quant01.691370/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/quant01.691370/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="691370" data-xf-init="member-tooltip" style="background-color: #525214; color: #d1d147"> <span class="avatar-u691370-m" role="img" aria-label="Quant01">Q</span> </a> </div> </div> <div class="message-userDetails"> <h4 class="message-name"><a href="/members/quant01.691370/" class="username " dir="auto" data-user-id="691370" data-xf-init="member-tooltip"><span itemprop="name">Quant01</span></a></h4> <h5 class="userTitle message-userTitle" dir="auto" itemprop="jobTitle">Newbie level 5</h5> </div> <img src="/styles/images/ranks/blevel2.gif" alt="Newbie level 5"> <div class="message-userExtras"> <dl class="pairs pairs--justified joinedBlock"> <dt>Joined</dt> <dd>Nov 13, 2024</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed"> <dt>Messages</dt> <dd>9</dd> </dl> <dl class="pairs pairs--justified"> <dt> Helped</dt> <dd>0</dd> </dl> <dl class="pairs pairs--justified"> <dt>Reputation </dt> <dd> <a href="/reputation/authors/quant01.691370" class="fauxBlockLink-linkRow u-concealed">0</a> </dd> </dl> <dl class="pairs pairs--justified"> <dt>Reaction score</dt> <dd>0</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed trophyBlock"> <dt>Trophy points</dt> <dd>1</dd> </dl> <dl class="pairs pairs--justified creditBlock"> <dt title="Activity points">Activity points</dt> <dd> <a href="/activity/" data-xf-click="overlay" class="fauxBlockLink-blockLink u-concealed"> 130 </a> </dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1783894" data-lb-caption-desc="Quant01 · Nov 14, 2024 at 8:32 AM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper"><blockquote data-attributes="member: 152255" data-quote="FvM" data-source="post: 1783890" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1783890" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1783890">FvM said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Without knowing the exact combination of generated frequencies, it's impossible to determine if it's regular interference or a generator artefact. You should also consider simple oscilloscope undersampling, does the modulation show with a spectrum analyzer or power meter? </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Hi FvM,<br /> I am quite confident in the fact that this is not an oscilloscope issue or any hardware issue other than the generator because I captured this beating on camera. I'm using the signal to diffract a laser with an acousto optic deflector, and the beam intensity, which is proportional to the amplitude of the of the input RF signal. When imaging the diffracted beams, I measured a sinusoidal intensity beating, of frequency around 300mHz.<br /> I actually tested the same signal using an AWG without the DDS option (so preprogramming all the sine waves and then sending them to the card) and the beating does not occur, all conditions equal otherwise. However it would be much more convenient for me to solve the beating issue than to forfeit the DDS.</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/reply?quote=1783894" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1783894/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div class="contentVote js-contentVote " data-xf-init="content-vote" data-content-id="post-1783894"> <meta itemprop="upvoteCount" content="0" /> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--up " data-vote="up"><span class="u-srOnly">Upvote</span></a> <span class="contentVote-score js-voteCount" data-score="0">0</span> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--down " data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="Quant01" data-content="post-1783896" id="js-post-1783896" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1783896/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/" /> <span class="u-anchorTarget" id="post-1783896"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783896" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2024-11-14T08:36:46+0000" data-time="1731573406" data-date-string="Nov 14, 2024" data-time-string="8:36 AM" title="Nov 14, 2024 at 8:36 AM" itemprop="datePublished">Nov 14, 2024</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783896" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1783896/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783896" rel="nofollow"> #9 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/quant01.691370/"> <meta itemprop="url" content="https://www.edaboard.com/members/quant01.691370/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/quant01.691370/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="691370" data-xf-init="member-tooltip" style="background-color: #525214; 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I assume it is just a measurement artefact.<br /> <br /> Still I don´t know what this means:<br /> <br /> <br /> Klaus </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>The DDS I'm using works with a given number of "cores", which are responsible for generating one waveform. So the output signal is the sum of the outputs of all the cores. Therefore when I say "asking for 5 sine waves" I'm programming 5 DDS cores to output one sine wave each. The DDS will combine them and output the result.</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/reply?quote=1783896" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1783896/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div class="contentVote js-contentVote " data-xf-init="content-vote" data-content-id="post-1783896"> <meta itemprop="upvoteCount" content="0" /> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--up " data-vote="up"><span class="u-srOnly">Upvote</span></a> <span class="contentVote-score js-voteCount" data-score="0">0</span> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--down " data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="kaz1" data-content="post-1783902" id="js-post-1783902" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1783902/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/" /> <span class="u-anchorTarget" id="post-1783902"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783902" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2024-11-14T10:32:25+0000" data-time="1731580345" data-date-string="Nov 14, 2024" data-time-string="10:32 AM" title="Nov 14, 2024 at 10:32 AM" itemprop="datePublished">Nov 14, 2024</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783902" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1783902/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783902" rel="nofollow"> #10 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/kaz1.623349/"> <meta itemprop="url" content="https://www.edaboard.com/members/kaz1.623349/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/kaz1.623349/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="623349" data-xf-init="member-tooltip" style="background-color: #cc6633; 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I will definitely try something along those lines. Hopefully I'll be able to extract some interesting information from that test.<br /> Best regards,<br /> Quant </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>It could be just visual artefact of sine wave addition:<br /> f1 = sin(2*pi*(0:1023)*.13);<br /> f2 = sin(2*pi*(0:1023)*.27);<br /> y = f1+f2;<br /> plot ( y)<br /> <br /> <div class="bbImageWrapper js-lbImage" title="1731580373904.png" data-src="https://www.edaboard.com/attachments/1731580373904-png.195369/" data-lb-sidebar-href="" data-lb-caption-extra-html="" data-single-image="1"> <img src="https://www.edaboard.com/attachments/1731580373904-png.195369/" data-url="" class="bbImage" data-zoom-target="1" style="" alt="1731580373904.png" title="1731580373904.png" width="592" height="457" loading="lazy" /> </div></div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div 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<meta itemprop="upvoteCount" content="0" /> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--up " data-vote="up"><span class="u-srOnly">Upvote</span></a> <span class="contentVote-score js-voteCount" data-score="0">0</span> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--down " data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="KlausST" data-content="post-1783908" id="js-post-1783908" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1783908/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/" /> <span class="u-anchorTarget" id="post-1783908"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783908" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2024-11-14T11:40:19+0000" data-time="1731584419" data-date-string="Nov 14, 2024" data-time-string="11:40 AM" title="Nov 14, 2024 at 11:40 AM" itemprop="datePublished">Nov 14, 2024</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783908" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1783908/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783908" rel="nofollow"> #11 </a> </li> </ul> </header> </div> 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</div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1783908" data-lb-caption-desc="KlausST · Nov 14, 2024 at 11:40 AM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper"><blockquote data-attributes="member: 691370" data-quote="Quant01" data-source="post: 1783896" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1783896" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1783896">Quant01 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> The DDS I'm using works with a given number of "cores", which are responsible for generating one waveform. So the output signal is the sum of the outputs of all the cores. Therefore when I say "asking for 5 sine waves" I'm programming 5 DDS cores to output one sine wave each. The DDS will combine them and output the result. </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>This means you have 5 DDS generating 5 independent sine waves and these 5 signals are sumed up.<br /> <br /> Do all DDS have a COMMON MASTER CLOCK?<br /> <br /> What are the exact frequencies?<br /> How are they sumed up?<br /> <br /> (Still I say the measurement artefact is the most probable cause)<br /> <br /> Klaus</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/reply?quote=1783908" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1783908/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div class="contentVote js-contentVote " data-xf-init="content-vote" data-content-id="post-1783908"> <meta itemprop="upvoteCount" content="0" /> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--up " data-vote="up"><span class="u-srOnly">Upvote</span></a> <span class="contentVote-score js-voteCount" data-score="0">0</span> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--down " data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="std_match" data-content="post-1783946" id="js-post-1783946" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1783946/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/" /> <span class="u-anchorTarget" id="post-1783946"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783946" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2024-11-15T07:22:16+0000" data-time="1731655336" data-date-string="Nov 15, 2024" data-time-string="7:22 AM" title="Nov 15, 2024 at 7:22 AM" itemprop="datePublished">Nov 15, 2024</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783946" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1783946/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1783946" rel="nofollow"> #12 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/std_match.333403/"> <meta itemprop="url" content="https://www.edaboard.com/members/std_match.333403/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/std_match.333403/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="333403" data-xf-init="member-tooltip" style="background-color: #336699; 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This will create some problems if the generator can't place an integer number of periods of the sine waves in the used sample memory.</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/reply?quote=1783946" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1783946/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget 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data-lb-caption-desc="FvM · Nov 15, 2024 at 7:35 AM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper">I read the generator datasheet so that it uses true DDS rather than replaying the waveform from memory <a href="https://spectrum-instrumentation.com/dl/m4i66_datasheet_english.pdf" target="_blank" class="link link--external" rel="noopener">https://spectrum-instrumentation.com/dl/m4i66_datasheet_english.pdf</a><br /> There are still ways to generate artifacts.</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a 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class="bbWrapper">Thank you all for your answers. <br /> To Klaus and Kaz1 : while I agree with the fact that sometimes (often) measurement artifacts of the oscilloscope lead to confusions in my case I have two reasons that make me quite certain that it is not the case. First, as I said, I observed the beating with 2 methods, the oscilloscope and via imaging of my laser beams on camera. Both measurements result in that beating. The second thing is that I programmed a similar experiment but without using a DDS (meaning that I programmed the entire waveform on the AWG instead of just specifying frequency, phase and amplitude). This results in the beating disappearing, leading me to believe that the cause of the issue is the way the cores interact with each other (because the AWG without DDS does not use such "cores" to produce the signal). So I don't think this is simply a measurement artifact. Or is there something I am missing ?<br /> <br /> To Klaus : to my knowledge, all the cores have the same master clock. For the summing up They are summed by bunches of 4. There are 20 available cores. Cores 0 to 3 produce a signal which is summed, same for 4 to 7, etc and then all these sums are then also summed to create the signal. A list of the exact frequencies that create the beating is :<br /> 45999999.85657632<br /> 47999999.951571226<br /> 50000000.04656613<br /> 52000000.14156103<br /> 53999999.94551763<br /> These are not all the frequencies for which the result occurs, but with these 5 you can get such behavior.<br /> <br /> To std_match : I have 20 cores available, and never went above this value. To be honest, I never planned to and do not know what will happen if I do. I feel like the card will prevent me from doing so but I am not sure.<br /> <br /> As Klaus suggested and considering my current results , I will investigate the core interactions and the way cores are summed.<br /> Thank you all for your input so far.<br /> <br /> Quant</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/reply?quote=1784069" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" 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itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1784075/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/" /> <span class="u-anchorTarget" id="post-1784075"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784075" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2024-11-18T07:20:56+0000" data-time="1731914456" data-date-string="Nov 18, 2024" data-time-string="7:20 AM" title="Nov 18, 2024 at 7:20 AM" itemprop="datePublished">Monday at 7:20 AM</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784075" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1784075/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784075" rel="nofollow"> #15 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/klausst.544298/"> <meta itemprop="url" content="https://www.edaboard.com/members/klausst.544298/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/klausst.544298/" class="avatar avatar--m" data-user-id="544298" data-xf-init="member-tooltip"> <img 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href="/reputation/authors/klausst.544298" class="fauxBlockLink-linkRow u-concealed">9,867</a> </dd> </dl> <dl class="pairs pairs--justified"> <dt>Reaction score</dt> <dd>5,769</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed trophyBlock"> <dt>Trophy points</dt> <dd>1,393</dd> </dl> <dl class="pairs pairs--justified creditBlock"> <dt title="Activity points">Activity points</dt> <dd> <a href="/activity/" data-xf-click="overlay" class="fauxBlockLink-blockLink u-concealed"> 175,784 </a> </dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1784075" data-lb-caption-desc="KlausST · Nov 18, 2024 at 7:20 AM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper">Hi,<br /> <br /> You see that´s why it´s important to give good informations (like numbers).<br /> <br /> The difference between these frequecies results in sideband frequencies. <br /> This is about 2MHz each time.<br /> <br /> More accurate: <br /> 2 000 000.094 994 90 Hz<br /> 2 000 000.094 994 91 Hz<br /> 2 000 000.094 994 90 Hz<br /> 1 999 999.803 956 60 Hz<br /> <br /> Let´s say the first three are identical. And they add up in amplitude.<br /> But the fourth is different by 0.291 038 30 Hz. (the 290mHz you see)<br /> <br /> So the resulting amplitude of the 2MHz will "pump" with a frequency of 0.290Hz from 2x to 4x the single amplitude.<br /> (Indeed also depends whether the high frequencies are all started at exactly the same time. Resulting in (2MHz) phase shift and thus modified total amplitude)<br /> <br /> This is my guess. But "guessing" means "not knowing" .. and thus always needs to be verified.<br /> Thus please try these frequencies (only the 5th is changed to get the equal difference frequency)<br /> 45999999.85657632 Hz<br /> 47999999.951571226 Hz<br /> 50000000.04656613 Hz<br /> 52000000.14156103 Hz<br /> 54000000.23655593 Hz <-- changed<br /> <br /> ... and give feedback on the results.<br /> <br /> Your results also clearly show whether it´s a measurement artefact or not. Now I´m rather convinced that my guess about "measurement artefact" is wrong.<br /> <br /> Klaus</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/reply?quote=1784075" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1784075/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div class="contentVote js-contentVote " data-xf-init="content-vote" data-content-id="post-1784075"> <meta itemprop="upvoteCount" content="0" /> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--up " data-vote="up"><span class="u-srOnly">Upvote</span></a> <span class="contentVote-score js-voteCount" data-score="0">0</span> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--down " data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="kaz1" data-content="post-1784081" id="js-post-1784081" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1784081/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/" /> <span class="u-anchorTarget" id="post-1784081"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784081" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2024-11-18T09:36:23+0000" data-time="1731922583" data-date-string="Nov 18, 2024" data-time-string="9:36 AM" title="Nov 18, 2024 at 9:36 AM" itemprop="datePublished">Monday at 9:36 AM</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784081" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1784081/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784081" rel="nofollow"> #16 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/kaz1.623349/"> <meta itemprop="url" content="https://www.edaboard.com/members/kaz1.623349/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/kaz1.623349/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="623349" data-xf-init="member-tooltip" style="background-color: #cc6633; color: #3d1f0f"> <span class="avatar-u623349-m" role="img" aria-label="kaz1">K</span> </a> </div> </div> <div class="message-userDetails"> <h4 class="message-name"><a href="/members/kaz1.623349/" class="username " dir="auto" data-user-id="623349" data-xf-init="member-tooltip"><span itemprop="name">kaz1</span></a></h4> <h5 class="userTitle message-userTitle" dir="auto" itemprop="jobTitle">Full Member level 6</h5> </div> <img src="/styles/images/ranks/flevel3.gif" alt="Full Member level 6"> <div class="message-userExtras"> <dl class="pairs pairs--justified joinedBlock"> <dt>Joined</dt> <dd>Aug 15, 2019</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed"> <dt>Messages</dt> <dd>393</dd> </dl> <dl class="pairs pairs--justified"> <dt> Helped</dt> <dd>19</dd> </dl> <dl class="pairs pairs--justified"> <dt>Reputation </dt> <dd> <a href="/reputation/authors/kaz1.623349" class="fauxBlockLink-linkRow u-concealed">37</a> </dd> </dl> <dl class="pairs pairs--justified"> <dt>Reaction score</dt> <dd>55</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed trophyBlock"> <dt>Trophy points</dt> <dd>28</dd> </dl> <dl class="pairs pairs--justified locationBlock"> <dt>Location</dt> <dd> <a href="/misc/location-info?location=UK" rel="nofollow noreferrer" target="_blank" class="u-concealed">UK</a> </dd> </dl> <dl class="pairs pairs--justified creditBlock"> <dt title="Activity points">Activity points</dt> <dd> <a href="/activity/" data-xf-click="overlay" class="fauxBlockLink-blockLink u-concealed"> 2,261 </a> </dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1784081" data-lb-caption-desc="kaz1 · Nov 18, 2024 at 9:36 AM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper"><blockquote data-attributes="member: 691370" data-quote="Quant01" data-source="post: 1784069" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1784069" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1784069">Quant01 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Thank you all for your answers.<br /> To Klaus and Kaz1 : while I agree with the fact that sometimes (often) measurement artifacts of the oscilloscope lead to confusions in my case I have two reasons that make me quite certain that it is not the case. First, as I said, I observed the beating with 2 methods, the oscilloscope and via imaging of my laser beams on camera. Both measurements result in that beating. The second thing is that I programmed a similar experiment but without using a DDS (meaning that I programmed the entire waveform on the AWG instead of just specifying frequency, phase and amplitude). This results in the beating disappearing, leading me to believe that the cause of the issue is the way the cores interact with each other (because the AWG without DDS does not use such "cores" to produce the signal). So I don't think this is simply a measurement artifact. Or is there something I am missing ?<br /> <br /> To Klaus : to my knowledge, all the cores have the same master clock. For the summing up They are summed by bunches of 4. There are 20 available cores. Cores 0 to 3 produce a signal which is summed, same for 4 to 7, etc and then all these sums are then also summed to create the signal. A list of the exact frequencies that create the beating is :<br /> 45999999.85657632<br /> 47999999.951571226<br /> 50000000.04656613<br /> 52000000.14156103<br /> 53999999.94551763<br /> These are not all the frequencies for which the result occurs, but with these 5 you can get such behavior.<br /> <br /> To std_match : I have 20 cores available, and never went above this value. To be honest, I never planned to and do not know what will happen if I do. I feel like the card will prevent me from doing so but I am not sure.<br /> <br /> As Klaus suggested and considering my current results , I will investigate the core interactions and the way cores are summed.<br /> Thank you all for your input so far.<br /> <br /> Quant </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>You can also confirm that a slow frequency is generated by checking with spectrum analyser. Or send this forum a small chunk of your final vector.<br /> If so then most likely it is a case of some feed through or pickup.<br /> <br /> frequencies do not add up or subtract unless they are mixed (multiplied) or there is non-linearity of amplifier (or DAC) but this would be more chaotic than just one slow harmonic.<br /> <br /> The relation of target frequency and DDS resolution will not cause that either, though the final frequency may be slightly different from target figure if target is not multiples of resolution.</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a 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data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="KlausST" data-content="post-1784107" id="js-post-1784107" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1784107/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/" /> <span class="u-anchorTarget" id="post-1784107"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784107" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2024-11-18T16:59:17+0000" data-time="1731949157" data-date-string="Nov 18, 2024" data-time-string="4:59 PM" title="Nov 18, 2024 at 4:59 PM" itemprop="datePublished">Monday at 4:59 PM</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784107" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1784107/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784107" rel="nofollow"> #17 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/klausst.544298/"> <meta itemprop="url" content="https://www.edaboard.com/members/klausst.544298/" /> <div class="message-avatar "> <div 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class="pairs pairs--justified"> <dt> Helped</dt> <dd>4,921</dd> </dl> <dl class="pairs pairs--justified"> <dt>Reputation </dt> <dd> <a href="/reputation/authors/klausst.544298" class="fauxBlockLink-linkRow u-concealed">9,867</a> </dd> </dl> <dl class="pairs pairs--justified"> <dt>Reaction score</dt> <dd>5,769</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed trophyBlock"> <dt>Trophy points</dt> <dd>1,393</dd> </dl> <dl class="pairs pairs--justified creditBlock"> <dt title="Activity points">Activity points</dt> <dd> <a href="/activity/" data-xf-click="overlay" class="fauxBlockLink-blockLink u-concealed"> 175,784 </a> </dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1784107" data-lb-caption-desc="KlausST · Nov 18, 2024 at 4:59 PM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper"><blockquote data-attributes="member: 623349" data-quote="kaz1" data-source="post: 1784081" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1784081" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1784081">kaz1 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> frequencies do not add up or subtract unless they are mixed (multiplied) </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>You are correct, no new frequencies get generated when signals are added. <br /> So, indeed no sidebands are generated. Thanks for clearing this up.<br /> <br /> However...<br /> ... on the scope you see the envelope (beating) of two added high frequency signals. And this envelope wobbles up and down with the difference frequency.<br /> <br /> You can see the 20MHz envelope .. when you adjust the time setup accordingly ...<br /> And you can see the 290mHz envelope ... when you adust the time setup accordingly.. (it´s the beating of the beating)<br /> <br /> ***<br /> Would be interested to hear about the "verification" results (requested in post#15)<br /> <br /> Klaus</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/reply?quote=1784107" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1784107/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div class="contentVote js-contentVote " data-xf-init="content-vote" data-content-id="post-1784107"> <meta itemprop="upvoteCount" content="0" /> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--up " data-vote="up"><span class="u-srOnly">Upvote</span></a> <span class="contentVote-score js-voteCount" data-score="0">0</span> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--down " data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="Quant01" data-content="post-1784145" id="js-post-1784145" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1784145/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/" /> <span class="u-anchorTarget" id="post-1784145"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784145" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2024-11-19T05:20:33+0000" data-time="1731993633" data-date-string="Nov 19, 2024" data-time-string="5:20 AM" title="Nov 19, 2024 at 5:20 AM" itemprop="datePublished">Tuesday at 5:20 AM</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784145" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1784145/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784145" rel="nofollow"> #18 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/quant01.691370/"> <meta itemprop="url" content="https://www.edaboard.com/members/quant01.691370/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/quant01.691370/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="691370" data-xf-init="member-tooltip" style="background-color: #525214; color: #d1d147"> <span class="avatar-u691370-m" role="img" aria-label="Quant01">Q</span> </a> </div> </div> <div class="message-userDetails"> <h4 class="message-name"><a href="/members/quant01.691370/" class="username " dir="auto" data-user-id="691370" data-xf-init="member-tooltip"><span itemprop="name">Quant01</span></a></h4> <h5 class="userTitle message-userTitle" dir="auto" itemprop="jobTitle">Newbie level 5</h5> </div> <img src="/styles/images/ranks/blevel2.gif" alt="Newbie level 5"> <div class="message-userExtras"> <dl class="pairs pairs--justified joinedBlock"> <dt>Joined</dt> <dd>Nov 13, 2024</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed"> <dt>Messages</dt> <dd>9</dd> </dl> <dl class="pairs pairs--justified"> <dt> Helped</dt> <dd>0</dd> </dl> <dl class="pairs pairs--justified"> <dt>Reputation </dt> <dd> <a href="/reputation/authors/quant01.691370" class="fauxBlockLink-linkRow u-concealed">0</a> </dd> </dl> <dl class="pairs pairs--justified"> <dt>Reaction score</dt> <dd>0</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed trophyBlock"> <dt>Trophy points</dt> <dd>1</dd> </dl> <dl class="pairs pairs--justified creditBlock"> <dt title="Activity points">Activity points</dt> <dd> <a href="/activity/" data-xf-click="overlay" class="fauxBlockLink-blockLink u-concealed"> 130 </a> </dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1784145" data-lb-caption-desc="Quant01 · Nov 19, 2024 at 5:20 AM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper">Hi,<br /> <br /> You were indeed correct Klaus, it was the "beating of the beating" that I was observing. Implementing the correction you mentioned results in the low frequency beating disappearing from the signal. More generally, correcting all frequencies such that they are multiples of the resolution and making sure that their differences are all large (in my setup, on the MHz scale) seems to clear up the issue.<br /> Thank you all for your help.</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/reply?quote=1784145" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1784145/quote">Reply</a> </div> </div> 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class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1784147" data-lb-caption-desc="D.A.(Tony)Stewart · Nov 19, 2024 at 5:46 AM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper">Does a simulation reveal any IMD near 0? That's a lot of variables.<br /> Did you look at the FFT results?<br /> <br /> Are any of these sources sensitive to this interference pattern?</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/reply?quote=1784147" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1784147/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div class="contentVote js-contentVote " data-xf-init="content-vote" data-content-id="post-1784147"> <meta itemprop="upvoteCount" content="0" /> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--up " data-vote="up"><span class="u-srOnly">Upvote</span></a> <span class="contentVote-score js-voteCount" data-score="0">0</span> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--down " data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="kaz1" data-content="post-1784164" id="js-post-1784164" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1784164/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/" /> <span class="u-anchorTarget" id="post-1784164"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784164" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2024-11-19T10:10:56+0000" data-time="1732011056" data-date-string="Nov 19, 2024" data-time-string="10:10 AM" title="Nov 19, 2024 at 10:10 AM" itemprop="datePublished">Tuesday at 10:10 AM</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784164" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1784164/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/post-1784164" rel="nofollow"> #20 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/kaz1.623349/"> <meta itemprop="url" content="https://www.edaboard.com/members/kaz1.623349/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/kaz1.623349/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="623349" data-xf-init="member-tooltip" style="background-color: #cc6633; 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Implementing the correction you mentioned results in the low frequency beating disappearing from the signal. More generally, correcting all frequencies such that they are multiples of the resolution and making sure that their differences are all large (in my setup, on the MHz scale) seems to clear up the issue.<br /> Thank you all for your help. </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>I see you imply modulation products (IMD) to blame rather than feed through/pickup. These products only occur if there is non-linearity. Additionally any DAC Fs also acts as modulating frequency. 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title="Alpha"> </div> </li> <li title="\beta"> <div title="Beta"> </div> </li> <li title="\gamma"> <div title="Gamma"> </div> </li> <li title="\delta"> <div title="Delta"> </div> </li> <li title="\epsilon"> <div title="Epsilon"> </div> </li> <li title="\varepsilon"> <div title="Alternative Epsilon"> </div> </li> <li title="\theta"> <div title="Theta"> </div> </li> <li title="\kappa"> <div title="Kappa"> </div> </li> <li title="\lambda"> <div title="Lambda"> </div> </li> <li title="\mu"> <div title="Mu"> </div> </li> <li title="\nu"> <div title="Nu"> </div> </li> <li title="\pi"> <div title="Pi"> </div> </li> <li title="\rho"> <div title="Rho"> </div> </li> <li title="\sigma"> <div title="Sigma"> </div> </li> <li title="\tau"> <div title="Tau"> </div> </li> <li title="\phi"> <div title="Phi"> </div> </li> <li title="\varphi"> <div title="Alternative Phi"> </div> </li> <li title="\psi"> <div title="Psi"> </div> </li> <li title="\omega"> <div title="Omega"> </div> </li> <li title="\Gamma"> <div title="Capital Gamma"> </div> </li> <li title="\Delta"> <div title="Capital Delta"> </div> </li> <li title="\Lambda"> <div title="Capital Lambda"> </div> </li> <li title="\Phi"> <div title="Capital Phi"> </div> </li> <li title="\Psi"> <div title="Capital Psi"> </div> </li> <li title="\Omega"> <div title="Capital Omega"></div> </li> <li title="\propto"> <div title="Proportional to"></div> </li> <li title="\neq"> <div title="Not equal"></div> </li> <li title="\equiv"> <div title="Equivalent"></div> </li> <li title="\approx"> <div title="Approximate"></div> </li> <li title="\cong"> <div title="Congruent or Isomorph"></div> </li> <li title="\leqslant"> <div title="Less than or equal to"></div> </li> <li title="\geqslant"> <div title="Greater than or equal to"></div> </li> <li title="\ll"> <div title="Much less than"></div> </li> <li title="\gg"> <div title="Much greater than"></div> </li> <li title="\subset"> <div title="Sub-set"></div> </li> <li title="\in"> <div title="In"></div> </li> <li title="\notin"> <div title="Not in"></div> </li> <li title="\forall"> <div title="For all"></div> </li> <li title="\exists"> <div title="Exists"></div> </li> <li title="\nexists"> <div title="Not exists"></div> </li> <li title="\emptyset"> <div title="Empty set"></div> </li> <li title="\pm"> <div title="Plus or minus"></div> </li> <li title="\mp"> <div title="Minus or plus"></div> </li> <li title="\times"> <div title="Times (cross product)"></div> </li> <li title="\cdot"> <div title="Dot (scalar product)"></div> </li> <li title="\otimes"> <div title="Direct product"></div> </li> <li title="\oplus"> <div title="Direct sum"></div> </li> <li title="\mathrm{d}"> <div title="Differential"></div> </li> <li title="\partial"> <div title="Partial"></div> </li> <li title="\frac{\mathrm{d} #}{\mathrm{d} }"> <div title="Total derivative"> </div> </li> <li title="\frac{\partial #}{\partial }"> <div title="Partial derivative"> </div> </li> <li title="\nabla"> <div title="Nabla"></div> </li> <li title="\to"> <div title="Tends to"></div> </li> <li title="\mapsto"> <div title="Maps to"></div> </li> <li title="\leftarrow"> <div title="Left arrow"></div> </li> <li title="\uparrow"> <div title="Up arrow"></div> </li> <li title="\downarrow"> <div title="Down arrow"></div> </li> <li title="\Rightarrow"> <div title="Double right arrow"></div> </li> <li title="\Leftrightarrow"> <div title="Double left and right arrow"></div> </li> <li title="\xrightarrow{#}"> <div title="Extensible right arrow"> </div> </li> <li title="\circlearrowleft"> <div title="Circle arrow left"></div> </li> <li title="\circlearrowright"> <div title="Circle arrow right"> </div> </li> </ul> </div> </div> </div> </div> </div> </div> </div> </form> <div class="block" data-widget-id="47" data-widget-key="xfes_thread_view_below_quick_reply_similar_threads" data-widget-definition="xfes_similar_threads"> <div class="block-container"> <h3 class="block-minorHeader">Similar threads</h3> <ul 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Are you sure you want to submit this form?", attach: "Attach files", rich_text_box: "Rich text box", close: "Close", link_copied_to_clipboard: "Link copied to clipboard.", text_copied_to_clipboard: "Text copied to clipboard.", loading: "Loading…", you_have_exceeded_maximum_number_of_selectable_items: "You have exceeded the maximum number of selectable items.", processing: "Processing", 'processing...': "Processing…", showing_x_of_y_items: "Showing {count} of {total} items", showing_all_items: "Showing all items", no_items_to_display: "No items to display", number_button_up: "Increase", number_button_down: "Decrease", push_enable_notification_title: "Push notifications enabled successfully at Forum for Electronics", push_enable_notification_body: "Thank you for enabling push notifications!", pull_down_to_refresh: "Pull down to refresh", release_to_refresh: "Release to refresh", refreshing: "Refreshing…" , "svStandardLib_time.day": "{count} day", "svStandardLib_time.days": "{count} days", "svStandardLib_time.hour": "{count} hour", "svStandardLib_time.hours": "{count} hours", "svStandardLib_time.minute": "{count} minutes", "svStandardLib_time.minutes": "{count} minutes", "svStandardLib_time.month": "{count} month", "svStandardLib_time.months": "{count} months", "svStandardLib_time.second": "{count} second", "svStandardLib_time.seconds": "{count} seconds", "svStandardLib_time.week": "time.week", "svStandardLib_time.weeks": "{count} weeks", "svStandardLib_time.year": "{count} year", "svStandardLib_time.years": "{count} years" }); </script> <form style="display:none" hidden="hidden"> <input type="text" name="_xfClientLoadTime" value="" id="_xfClientLoadTime" title="_xfClientLoadTime" tabindex="-1" /> </form>  <script type="application/ld+json"> { "@context": "https://schema.org", "@type": "QAPage", "url": "https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/", "mainEntity": { "@type": "Question", "@id": "https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/", "name": "Low frequency modulation in high frequency DDS generated signal", "datePublished": "2024-11-13T11:39:30+00:00", "url": "https://www.edaboard.com/threads/low-frequency-modulation-in-high-frequency-dds-generated-signal.413002/", "text": "Hi all, \nRecently, I posted the following message on another forum and was advised to ask around in a DSP forum :\n\n\"I've been using an arbitrary waveform generator for one of my projects, and specifically, I'm using a DDS option on that AWG (the waveform generator is an M4i6621x8 from Spectrum Instrumentation). Essentially, I'm sending asking the DDS to output a sum of RF sine waves, all of them being on the order of 10s of MHz, with a delta in frequency of at least 1Mhz. However, on the output signal, if I ask for a certain amount of sin waves (usually 5 or more), I start observing a modulation of the amplitude of frequency a few hundred mHz (orders of magnitude away from my input frequencies). The modulation is sinusoidal.\nMy questions are : why does this happen and how can I remove this feature ? I would expect some MHz beating because of how sum of sine functions work, but definitely not mHz. \nSome additional information : \n-the frequency resolution of the DDS is about 290 mHz, so this value seems to fit with the observed beating, but I fail to see how this could be related to the issue. \n-I didn't notice such beating when using less than 5 frequencies as an input. \n-I am using a ZHL-1-2W+ power amplifier at the output of the AWG, which is then connected to an acousto optic deflector (a device that diffracts a laser beam according to input frequencies). The amplitude modulation becomes visible on camera based on the intensity of the diffracted beams.\"\n\nIf anyone knows how to solve this issue or has any idea, it would be greatly appreciated. \nThanks in advance.", "answerCount": 35, "upvoteCount": 0, "author": { "@type": "Person", "@id": "https://www.edaboard.com/members/quant01.691370/", "name": "Quant01", "url": "https://www.edaboard.com/members/quant01.691370/" }, "suggestedAnswer": [ { "@type": "Answer", "datePublished": "2024-11-23T11:53:25+00:00", "url": "https://www.edaboard.com/posts/1784456/", "text": "Low-frequency modulation in DDS-generated signals often arises from DDS resolution limits, amplifier nonlinearity, or measurement artifacts like oscilloscope undersampling. Verifying with a spectrum analyzer and adjusting DDS settings can help. Using a linear amplifier or phase dithering may reduce intermodulation distortion (IMD), especially in precision applications like laser systems", "upvoteCount": 0, "author": { "@type": "Person", "@id": "https://www.edaboard.com/members/firaconsortium.691613/", "name": "Firaconsortium", "url": "https://www.edaboard.com/members/firaconsortium.691613/" } }, { "@type": "Answer", "datePublished": "2024-11-23T01:42:36+00:00", "url": "https://www.edaboard.com/posts/1784425/", "text": "Hi,\n\nD.A. (Tony) Stewart: for certain different frequencies (other than the ones I specified for Klaus earlier) the beating does occur but usually at 290mHz. From my resent testing of different scenarios based on Klaus' idea, it looks like the beating occurs at the frequency corresponding to the greatest common denominator of the input frequencies. Usually it is 290mHz because this corresponds to the resolution of the DDS, but I guess by pure chance it could happen at another frequency. And if you're referring to the patterns visible on the oscilloscope, apart from phase, they are always similar. I don't know if this answers your question ?\n\n\nNot quite. My hypothesis is interference patterns from sub-sampling with inadequate 100 MB buffer length to resolve 10's of MHz and 0.29 Hz at the same time.\n\nI made discrete signals on Falstad's Analog simulator site, then it prompted me to increase the BW (or sampling rate as Falstad Sim only has a small buffer for browser simulation. But after, If I reduce the sampling rate 3 orders of magnitude from 3.125 ns to ms, I see the interference pattern as baseband. Only one signal had a 0.254 Hz offset . You can expect up to N multiples of the resolution with N signal sources.\n\nThis is the way old sub-sampling GHz scopes would work with fast capture but slow sampling rate.\n\nDoes that describe your capture?\n\n\nsim https://tinyurl.com/2apq4qnq", "upvoteCount": 0, "author": { "@type": "Person", "@id": "https://www.edaboard.com/members/d-a-tony-stewart.134022/", "name": "D.A.(Tony)Stewart", "url": "https://www.edaboard.com/members/d-a-tony-stewart.134022/" } }, { "@type": "Answer", "datePublished": "2024-11-22T14:01:33+00:00", "url": "https://www.edaboard.com/posts/1784374/", "text": "Also ADC clock frequency can modulate your tones.\nThe power amplifier may behave better if you randomise the phase to reduce peak/average, and dither each tone", "upvoteCount": 0, "author": { "@type": "Person", "@id": "https://www.edaboard.com/members/kaz1.623349/", "name": "kaz1", "url": "https://www.edaboard.com/members/kaz1.623349/" } } ] }, "publisher": { "@type": "Organization", "name": "Forum for Electronics", "description": "International Electronics Discussion Forum: EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals", "url": "https://www.edaboard.com" } } </script> <script> $(function(){ var notice = $('.xb-welcome-notice'); if(notice.length){ var cookie = XF.Cookie.get('hide_welcome_notice'); if(!cookie){ XF.Cookie.set('hide_welcome_notice', Date.now()); notice.show(); } else if ((Date.now() - cookie) > 8.64e+7){ XF.Cookie.set('hide_welcome_notice', Date.now()); notice.show(); } else { notice.hide(); } } }); </script> </div> </body> </html>

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Low frequency modulation in high frequency DDS generated signal | Forum for Electronics