First HF receiver build

This is the finished board -- it's an HF receiver (think "shortwave radio"). If you look really closely, you'll see some bodges and fixes. I'm amazed it works, given how little I know! This is an initial proof of concept before I commit to a larger scale receiver, and start playing with some more advanced concepts. Out of frame is the Teensy microcontroller board that is controlling everything.

The design is an unbalanced Tayloe detector, with two gain stages. Total system gain should be something like 64dB. The output is a pair of AF baseband signals, representing I and Q for processing off-board.

The implementation is almost entirely SMD, with just a few odds and ends on the top. I had no idea the capacitors were that big when I ordered them (220nF C0G caps are pricey and sizeable!). The LO is generated by a common Si5351 synthesizer module, input is at the SMA connector, and output is the audio jack.

For initial testing, I put together a quick GNURadio flowgraph to take the I and Q streams and unite them for complex processing. The high pass filter is to filter out the DC component, which dominates the graphs if I don't remove it.

And running for a couple hours at 7.074 MHz, there's a lot of FT8 and other digital mode activity. I'm absolutely thrilled that my poor modicum of knowledge has achieved such excellent sideband isolation! Some of this testing is just to get an idea what kind of system gain I need to get reasonable AF levels, and the results are excellent!

And for a more familiar depiction of the results, here's the in-phase channel pumped into WSJT-X. This makes it more of a DSB receiver, so the LSB stuff is mixed in. But I've decoded thousands of FT8 packets in the last couple hours, and it seems to be working quite well. I'll have to do a raft of more rigorous and scientific tests to see how it's performing, but I just couldn't wait to see pretty waterfalls with it!