Poor Man's Panadapter?
Bruce MacKinnon KC1FSZ
Here's an experiment that might be of interest, especially to anyone thinking about one of those fancy ICOM 73000000s. The goal is to build a crude panadapter into my BITX rig without resorting to external PCs, SDR dongles, etc. I am using a few cheats in my scratch-build BITX that may make this tricky on a stock unit, but I'm sure the group can figure out how to expand this into the mainstream.
It's a bit like a Sweeperino I guess. I've built my firmware to quickly sweep the VFO across the band of interest (40m phone in my case) and then to look at the AF spectrum at each point and display the result in a simplistic spectrum display. Obviously, this interrupts the receive for a brief instant when it is happening, but I've also set things up with an extra MOSFET so that the audio output can be suppressed during the sweep to hide the annoying sounds. You probably have this mod in your rig anyhow if you've added an AGC.
I think the most sophisticated way to go is to do some DSP fiddling of the overlapping 3 kHz segments of the spectrum that are sampled during the sweep. At the moment I am sweeping in 500 Hz steps so there is overlap in the samples of the audio. This needs some more experimentation to get the optimal sweep speed, the cleanest way to stitch things together, averaging, etc. but even something basic is good enough to show the activity on the band.
There's another thread going right now talking about the use of the Teensy processor, which I completely endorse. I've used the 3.2 in all of my various BITX builds and find the added versatility of being able to do DSP very useful. I'm not a DSP expert by any means, but there is some great capability on the Teensy boards.
I have also been using a 128x64 OLED display which makes these simple graphics possible. I know ... it's noisy. You guys with the giant color TFTs displays could make something even cooler I'm sure.
Here's what my initial display looks like. The caret at the very bottom is pointing to where the VFO is currently set. You know it's working because you can always see the signature 7199 BITX birdie!
This link is to a video that was made with the sweep slowed and the audio on so you can hear how it works. It sounds like a strange SSTV mode, but it's actually the entire 40m phone band being analyzed for activity: https://www.youtube.com/watch?v=YS-Gp-PJmuk
More to follow if I can improve this.
Bruce KC1FSZ https://www.qrz.com/lookup/kc1fsz