Monday, June 4, 2007

DC 40 - A Direct Conversion Receiver

I have just posted a new project on my website:
A simple direct conversion receiver
  • You can assemble it in one evening. Just six transistors and any audio amp IC.
  • It does not use any special components. All out of your junk box.
  • Quite a performer. It will probably beat your general coverage, synthesized all mode transceiver with its reception.
The article also traces our journey from idea to finishing the project.

2 comments:

Jason said...

FB on your DC RX and the excellent writeup. There's nothing quite like the clean sound of a DC RX compared to a filtered and processed superhet. How was your experience with the VFO stability? I'm working on developing a DC rig in a similar vein, and the LO has been the biggest challenge. I would like a decent amount of tuning range and stability, with the restriction of using common parts. I'm leaning towards using a polyvaricon cap as the tuning element in a VFO, but I have also been considering the use of a ceramic resonator VXO. 73 de NT7S.

Farhan said...

The VFO stability was an issue until I shielded it. It still drifts a bit for a few minutes.
The major part of instability is due to poor temperature compensation of capacitors and inductors. In capacitors we don't usually have a choice given our limited junkboxes. But we can surely improve upon the inductors. The newer toroidal materials have quite good temperature tolerance.
If you don't have access to them, it is best to go for air core coils. Choose a coil former that doesn't expand with heat. I would recommend making one out of discarded x-ray sheets.