Sunday, March 05, 2023

Soldersmoke Direct Conversion Receiver working

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!


1 comment:

Bill Meara said...

Excellent Peter! You are almost there! Just a few more steps and you will have a useable receiver:
-- 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