Tone or birdie every 500 Hz in USB mode
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My guess is that DIGI mode has a wider bandwidth so more noise. This will cause AGC to cut the gain a little bit and the spurs will appear reduced.
Tony
AD0VC
From: [email protected] <[email protected]> on behalf of Erik Larson via groups.io <kd7ykq@...>
Sent: Wednesday, April 2, 2025 11:27 AM To: [email protected] <[email protected]> Subject: Re: [QRPLabs] Tone or birdie every 500 Hz in USB mode ?
For some reason I cannot get audacity to record from the QMX.. But WSJT-X sees it fine (yes, I closed WSJT-X first before trying Audacity). So no audio recordings but another picture. Mel, mine sounds very similar to yours.
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I have confirmed that the pulsating tone noise at 1Khz was from the GPS module, as with it removed the noise at 1Khz is markedly reduced. I will run it this way in the morning and see if it is better able to decode MSK144 without that persistent pulsating
noise at 1KHz. I still see less of these noise lines in DIGI mode than in either USB or LSB, so I think there is something different with the RX audio? in DIGI that might help with USB also if I can figure out what the difference is.
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I can also confirm that the CW sounding noise was from the GPS, however after removing the GPS, there is still a high pitched tone on 12m and 6 meters that wasn't there before. I think it's on all bands above 17 meters, but the noise is higher on 17 meters and 10 meters, even with the dummy load, so it's hard to hear the tone on those bands.
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73, Dan - W2DLC |
Daniel Conklin