QMX Hi Band V2 Receive Sensitivity
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Hi Mike. Compared to my High Band QMX, yours seems to be at least 30 dB in the deaf direction. In your case I don't think it has anything to do with the lowpass filters because your output power measurements are very good. I rather suspect your issue is in the bandpass filter circuit. Thoroughly re-check L401, C401-C404 and all associated connections. Also check T401. Lots of potential enamel removal possibilities here. If nothing wrong there, use the schematic and verify continuity from the gate of Q508 to the "RXIN" lead of L401. Verify proper operation of Q508. This FET turns the receive RF path off during transmit. It could be off all the time. Good luck .... Ron On Sun, Mar 3, 2024 at 2:16?PM N0MPM <n0mpm52@...> wrote: I have seen quite a few a few posts on sensitivity on the High Band QMX, but I am not too sure what to do if it isn't up to snuff...My Low Band QMX sensitivity is about -107 to -109 dbm at the antenna bnc connector.? My new High Band QMX is running only about -75 to -77 dbm.? Not deaf by all means, but I am guessing it should be better.? Is this something that can be improved by fiddling around with the LPF windings?? Transmitter power is about 3.8 to 4.2 watts depending on band with the 9v transformer winding.... |
Ronald Taylor