Mixer Waveforms

Submitted by rfrobenius on Fri, 03/18/2016 - 10:43

&amp;lt;h2&amp;gt;Background&amp;lt;/h2&amp;gt; This example shows the effect of a switching mixer that inverts the RF signal based on the sign of the LO (local oscillator). The RF signal is unchanged when the LO is positive, and it is inverted when the LO is negative, resulting in a waveform that will have frequency components at the sum and difference frequencies of the RF and LO (RF + LO, RF - LO). Since there are sharp discontinuities in the waveform, many other harmonic components will be present as well. All signals that are not to be used will have to be filtered out. &amp;lt;h2&amp;gt;Video&amp;lt;/h2&amp;gt; Watch a &amp;lt;a data-cke-saved-href="/node/220" href="/node/220"&amp;gt;brief video describing this demo&amp;lt;/a&amp;gt;. &amp;lt;h2&amp;gt;Exercise&amp;lt;/h2&amp;gt; Try setting the RF to 3 and the IF to 1 and click the update button. You should be able to see how the blue RF wave gets inverted whenever the green LO wave becomes negative. Now try setting the RF to 30 and the IF to 28. You should be able to see that the blue RF wave traces out a difference frequency of about 2 Hz, while also having peaks repeating at 58 Hz. &amp;lt;p&amp;gt;This demo is included in the &amp;lt;a data-cke-saved-href="<a href="http://www.rfmentor.com/node/122">http://www.rfmentor.com/node/122</a>" href="<a href="http://www.rfmentor.com/node/122">http://www.rfmentor.com/node/122</a>"&amp;gt;Online RF Technology Certification program&amp;lt;/a&amp;gt; from Besser Associates.&amp;lt;/p&amp;gt; &amp;lt;img data-cke-saved-src="<a href="http://www.rfmentor.com/sites/default/files/RF%20Tech%20Cert%20Logo.jpg">http://www.rfmentor.com/sites/default/files/RF%20Tech%20Cert%20Logo.jpg</a>" src="<a href="http://www.rfmentor.com/sites/default/files/RF%20Tech%20Cert%20Logo.jpg">http://www.rfmentor.com/sites/default/files/RF%20Tech%20Cert%20Logo.jpg</a>"/&amp;gt; &amp;lt;iframe src="/sites/default/files/calcs/FExp/mixerMult.html" width="100%" height="610px" frameborder="0" /&amp;gt; &amp;lt;h2&amp;gt;Background&amp;lt;/h2&amp;gt; The second example shows the effect of a mixer that simply multiplies the RF signal with the LO (local oscillator). The result is also a waveform that will have frequency components at the sum and difference frequencies of the RF and LO (RF + LO, RF - LO). This is an idealized version of what happens in a mixer that uses nonlinearities to mix the two signals. &amp;lt;h2&amp;gt;Exercise&amp;lt;/h2&amp;gt; Suggested values: Try setting the RF to 5 and the IF to 4 and click the update button - you can see the blue product waveform clearly. The red dotted line shows the difference frequency. Now try setting the RF to 20 and the IF to 19. This combination of frequencies allows you to see the difference frequency more clearly while still seeing the other frequency components.

Comments

Problem fixed

Submitted by rfrobenius on Thu, 04/07/2016 - 14:30

There was a temporary problem with the mixer not working due to an update I made to another project. I've now fixed that issue and it seems to be working again.

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