A simple demonstration here showing the result of mixing two GHz signals together. One is 3.001 GHz and the other is 3.000 GHz. It follows on from my earlier experiments using a Teensy 3.1 to control an ADF4351 GHz signal generator via the SPI bus. (See https://forum.pjrc.com/threads/55323...th-GHz-signals).

I built two such signal generators for this experiment - one to act as a local oscillator, and the other to act as an RF input source. Outputs from these are fed to the RF and LO inputs of a AD8342 RF Mixer evaluation board via short lengths of RG316 50 ohm cable. The mixer board only requires a single 5 volt d.c. supply. Its output is known as IF (Intermediate Frequency) and consists essentially of the difference frequency between the two inputs, which in this case is 3001 MHz - 3000 MHz = 1 MHz. The 1 MHz output is displayed on my scope.

The complete test setup is shown in this next picture. I'm using two copies of a serial port program running on a tablet to set the desired output frequencies. Power levels are lowest settings of -4dBm (about 400 mV pk-pk amplitude).

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The AD8342 uses the principle of a "Gilbert Cell" to do the mixing and works with inputs from low frequencies up to around 4 GHz. It also has a built-in amplifier for the LO input so you don't need high power (as with some mixers). The amplitude of the output in this experiment is amazingly high - 4 volts pk-pk.

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This setup has some interesting further uses. By inserting a test design circuit in between the signal generator output and the RF input to the mixer, then you could plot the effects of the test circuit over a wider GHz frequency range, yet still see the output on a simple scope. You would need to adjust the frequency of both generators simultaneously in sort of "tracking mode", but the results would be directly observable at the lower frequency of the mixer output.