I didn't have a smooth run with this project, despite the best of help. Here's how it sounds now:
My tuning is very sensitive but at least it doesn't drift like it was with the original (not NP0) capacitors.
I ran into a few issues along the way that took me way too long to debug:
- The audio chain was taking off at about 2MHz and upsetting the VFO via the power line.
- I didn't use NP0 caps in the VFO and it was incredibly unstable at first.
- The variable linear power supply I was using caused great audio hum - no idea why - another supply and the hum is gone.
My build is not very sensitive. I suspect I have the wrong diodes in the ring mixer.
My thanks to Stephen, VK2BLQ, for suggesting the addition of a 1k resistor to isolate the early stages of the audio chain from the output stage to stop the instability. And, of course, thanks to Bill for the design of this project!
Excellent Peter! You are almost there! Just a few more steps and you will have a useable receiver:
ReplyDelete-- Mechanical stability is very important. Get yourself a small piece of wood and screw your boards onto it.
-- Clean up the wiring! There are too many leads floating around.
-- Stop using the AC power supply. You can run the whole receiver off a single square 9 volt battery.
-- The tuning can seem a bit jumpy but mechanical stability will take care of this: Make yourself a simple front panel. Drill a hole just large enough for the screw. Attach the panel to the board so that it puts a bit of downward pressure on the screw. This will prevent the screw from wobbling about inside the nuts and will make for easier tuning.
Please send us updates.
I showed a picture of your receiver to our students during our last session with them.
73 Bill N2CQR