There comes a time when you build something to just understand it, tonight was one of those nights for me. I mostly use mini circuits mixers in my home brew as they are cheap and convenient, but tonight i build a diode ring mixer just to learn about how they really work and understand the principles involved.
So i laid out the circuit in Spring Layout.
Routed out the board, wound the transformers and assembled the few other bits and bobs i needed.
Assembled the board and used a sharpie for my very professional looking silk screen HIHI.
Next step was to feed the thing and check to see if it was actually working. LO was fed with 3v p-p at 8.4mhz from a DDS Signal Generator, RF was fed with 100mv at 1mhz and the IF was connected to a spectrum analyser to see what the output products were.
As you can see in the image above, we have the + and – peaks of the inputs showing in the spectrum analyser, 7.4 and 9.4 mhz. Harmonics are there but are orders of magnitude down on the desired signals. This surprised me a little as I expected greater harmonics with the 2 inputs not being 50 ohm terminated. LO was 200 ohm and RF has an unknown impedance, but i really should measure it just so i know.
All in all, this has been a very successful little project that produced good results and a very useable mixer.