开云体育

I read your blog entry with interest. I believe there must be a fault somewhere in your radio. The QCX receiver was designed with PLENTY of gain. I spent a lot of time studying other similar receiver architectures during the design process. One important consideration was, what total gain to provide. I always like to provide a little extra gain, because you never know what different people are using for antennas, and there is a huge range of sensitivity between different earphones, etc. So I configured the QCX design with 5-10dB more gain than other similar designs. I also felt justified in doing this because the very low noise HiFi op-amp LM4562 is used throughout - so providing additional gain which is later attenuated by the gain control does not damage overall sensitivity.?

These design considerations have also been confirmed by all feedback received so far (until yours, hi hi). I have received several comments from people who are operating the radio with the audio gain control barely off its minimum. Others have measured and confirmed the high sensitivity.?

So, according to the design and the results people are having - it seems to me that your experience is atypical and therefore suggests a fault somewhere. You should NOT need to add an LM386 to get sufficient gain <shudder /> the provided gain should be more than enough. Adding an LM386 masks the fault but does not address the underlying fault causing the low audio.?

I think that it would be worth re-checking T1, have you got all the windings correctly phased and is there DC continuity everywhere with good joints? Since you have an RF signal generator it would also be a good idea to trace the signal through the LPF and through the RxTx switch to make sure that there is not a fault there in Q5. I'm not sure what else to suggest but this should be a start. If you sent it to me I'd be happy to take a look at it, but postal times are likely rather slow.?

73 Hans G0UPL