开云体育

If incoming signals are too strong to go through the receiver without distortion, you need to reduce the gain. ?The bitx40 has an audio gain control already, that happens at the tail end of the radio. ?For really strong signals, we're better off with an RF gain control, RF gain happens at the front end of the receiver near the antenna. ?That way we don't overload all those parts of the receiver that happen before the audio gain control.

The first link talks about many different methods of gain control, including two methods of RF gain control. ?The one by Don Cantrell where you mess with power into the existing amplifier at Q1 is an elegant solution that probably works just fine. ?The second link is Don's blog post about it. ?The second RF gain control method is described in post 20538 and 20541 where you add a 10k pot between K2 pin 14 and K1 pin 12, that is a trace that is only used during receive and not during transmit. ?The second method is a bit harder to do well, because if you mount the 10k RF gain pot on the front panel it really should have two pieces of coax off to where you cut that trace between K1 and K2 since it is sometimes dealing directly with an extremely low level received signal from the antenna.

Adding a 240 ohm resistor at the antenna might work well enough if you have an antenna tuner between that and the rig to match the rig's 50 ohm transmitter. ?I suppose if you are talking to somebody close you want to reduce transmitted power anyway. ?But you will be wasting most of the power from the transmitter, better to reduce mike gain (or R136) if you want to cut transmitter power.
?

Jerry