Hello!
With the AGC mod from Don nd6t I have a lot of fun with my bitx40 again. Without this strong signals overdrive my RX path somewhere (in LM386?) that much that I had strong distortion with volume poti in round about the middle position and above.
But there are two other problems (maybe default bitx40 behaviour or a broken part??):
1st: My RX signal is very weak.
I checked out several small speakers but I need to set volume to max in any case. The bitx is then not as loud as a normal human voice nearby you. Maybe a transistor in the RX path is a problem? I feed a nf signal ~1kHz with some few mV into C116, C107 and C33. Everytime I get a loud and strong signal. On C31 I did not get a good/strong signal. Maybe in this stage is a problem? Is there a paper/wiki how I could nail this problem down? First I thought about another NF stage witha LM380. But after I get the loud signal with my testsignal I guess this is not needed.
2nd: "White noise"/hiss in the NF signal:
I tried to power the PA independend with > 12V for more HF output. This means: After the power plug I split the PWR IN with a LDO for the main 12V circuit and another wire without the LDO into the PA in. So fare, so good. The very interesting part is that I get high freq hiss in the RX signal path as soon as the input voltage exceeds the 12.0V out plus the drop voltage of the LDO. F.e. this means: Clear RX signal up to 12.7V and high freq noise up from here. The noise reaches its max volume about 13.0V. Is this a general problem as soon as I drive the PA with higher volume or is there a change to solve this issui with better groundings/shields..?
Best regards, 73 an thanks for help,
Stephan dc8lz
