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I have a code that sends a beacon every 1 minute with a data-rate of 1200bps (BPSK-G3RUH). I do receive the signal using a custom software defined ground station that also decodes the beacon. After a couple of minutes (10 - 30 minutes), my software defined ground station stops receiving the signal. Thus I used Airspy SDR to have a visual on the signal. This is the signal I see when I perfectly receive the signal. This is the signal I see after a few minutes.

The perfect signal has a higher peak and a longer duration.

enter image description here

While the one I cant decode has a flatter peak and 2 other smaller peaks to the right and to the left. enter image description here

My question is, what caused the signal to change like this? Could it possibly be a hardware problem from the transceivers or the antenna?

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    $\begingroup$ That could be anything, probably a software bug on the transmitting end, or a different baud rate, or a different pulse shaping filter. Might not even be broken, just something else! $\endgroup$ Mar 4 '20 at 14:41
  • $\begingroup$ Welcome to ham.stackexchange.com! $\endgroup$
    – rclocher3
    Mar 5 '20 at 17:26
  • $\begingroup$ It's hard to be sure the two images are to the same scale. Are they? $\endgroup$
    – Zeiss Ikon
    Mar 5 '20 at 19:54
  • $\begingroup$ @ZeissIkon yes they are $\endgroup$
    – Sarah
    Mar 8 '20 at 5:41
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I agree with @MarcusMüller - that could be anything. I would fistly look for some kind of overheating in the circuit. Also it's worth checking the SWR of the antenna. If your antenna uses some kind of transformer it might be overheating. Something can be wrong with the coax as well, e.g. poor connection, whater inside the coax, etc.

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Look for a buffer overflow, integer overflow, or numeric out-of-range error in your software. Are you trying to compute the sine or cosine of some massive huge number? (causing range reduction loss of precision due to some number you've been incrementing for 30 minutes).

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  • $\begingroup$ I actually do not perform any calculations, all I do is command my transceiver to send a beacon every 1 minute. I believe all these calculations are done within the transceiver. $\endgroup$
    – Sarah
    Mar 5 '20 at 6:56

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