I have got my BiTX40 board?all going in a nice box using an AD9850 DDS/PIC controller. Although it works pretty well? I do have a few issues that have annoyed me a little - and perhaps others here?may have resolved.
Audio hiss - not the LM386 ( I know the mod to drop its gain down). The hiss is already present on?its input, as a quick fix I put?small R/ C network across the VOL control? to roll?the treble off?- makes a huge difference. are they all?like this??
Carrier balance - on TX the carrier balance is poor?- listening on another RX it wont null out with the preset pot -? even my ancient tube rigs are better. I imagine its either mismatched diodes or a poorly wound toroid. I expected a couple of pf caps (one?variable) ?to ensure a good carrier null, but they are not present in the design.
Lastly - I found any condenser mic capsule I tried?sounded dreadful so went with a low imp dynamic comms mic and blocking cap..but I had to add a single transistor preamp to get enough gain.
