Hello Dex,
Try to use a bit larger bandwidth, and use the average power function
(avrg_n, see below). For FSK, MSK, and similar modes, the *power*
contained in the signal is independent of the modulation as long as the
frequency range covers most of that. Details about that function are here:
http://www.qsl.net/dl4yhf/speclab/interpr.htm#avrg_func
The problem is that the FSK bursts are relatively wide (~~ 150 Hz at
Markus' LF grabber), so to measure a constant power even during the
bursts, you would sacrifice some signal to noise ratio due to the wider
'receiver bandwidth'. Suggestion: Use a second channel which measures
the average power (instead of the peak voltage), and compare them over
some time. Hopefully the same diurnal variation is visible in both curves.
But there may be a different explanation (I admit, wild guesswork): Does
your receiver have an AGC ? If so, could there be some kind of beating
signals, causing the 'needle to move', which also affects the total gain
between antenna and audio output ? In that case other, sufficiently
strong 'carriers' would show the same pattern, which iirc was not the case.
All the best,
Wolf .
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