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MRX-40 Direct Conversion Receiver
I found this neat little project here. I tell ya, it was really fun building this receiver. Even though it can be built in one afternoon, I opted to take my time with it. I already have some mods in mind for it. Something about not having a trimmer cap in the SA612 front-end didn't sit well with me, and with good reason. Signal input is being severely attenuated because the pre-selector is pre-selecting in the wrong part of the band :-\ But that's ok, I'm going to add a small trimmer cap that will hopefully put it on the money...simply adjust for maximum noise.
The receiver has, what I thought to be, a pretty slick and simple VXO. It uses a simple rectifier diode, in my case a 1N4002, as a varactor tuning diode. This particular diode has a reverse-bias capacitance of about 15pF. Which makes me wonder, can I get 30pF by reverse biasing two of these diodes in parallel? Hmmmmm. The receiver tunes from 7.029MHz to 7.031MHz, conservatively speaking. Oh and another mod, changing out my pathetic-looking 2-turn FT37-61 with a molded 15uH inductor. And finally, a tunable CW audio filter I found from Barrie ARC. My wife is from Barrie, ON, so I thought it was pretty cool I found that :-) I'll shut up now and show you some pictures.
