I don't have any experience with chirps, but I can add this bit.
If you can hear the change, then the change can be seen on an FFT. At least that would give a sense of whether the shift is up or down, if it is difficult to tell by listening. An FFT could also be applied to the RF, but, as Victor mentioned, the shift is small wrt the TX freq. It is NOT small wrt the decoded audio, however, which is why it was reported. So an FFT may well find it. There are different ways to get that analysis, and might not be worth the effort. One method would be to use a modern scope with FFT; another, a software scope such as the Zeitnitz scope; another might be fldigi. In the last two cases, you'd have to pipe the audio...that is the RX decoded audio...into the audio line in on a computer.
But you still have to find out why...so maybe this FFT business isn't worth the effort...because you still then have to find the /cause/, even though you now have a pretty good idea where to look.
On 2020-07-14 18:15:+1000, you wrote:
>Generally a chirp would be due to an unstable power supply, resistance in
>the fuse holder, etc.. It can also be cause by poor decoupling/loading of
>the oscillator circuit, but in the case of a well-designed circuit like the
>K2, this would normally only arise with misplaced components or poor
>connections.
>
>On Tue, 14 Jul 2020 at 18:01, Victor Rosenthal 4X6GP <
[hidden email]>
>wrote:
>
>> A chirp can't be seen visually on an oscilloscope (well, maybe on a > panadpter or spectrum analyzer if it is a very big one).
>>
>> A chirp is a change in frequency of the transmitted signal. It is not > the same as a click, which is a wide signal caused by too-short rise and > fall times of the keyed envelope, or a badly shaped envelope. You can > see the envelope shape on an oscilloscope. But the change in frequency > caused by a chirp is very small in comparison with the frequency of the > signal.
>>
>> The way to detect a chirp is to listen to the transmitted signal on a > second receiver. Your ear is very sensitive to changes in pitch.
>>
>> 73,
>> Victor, 4X6GP
>> Rehovot, Israel
~R~
72/73 de Rich NE1EE
On the banks of the Piscataqua
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