15 October 2015

how fading or AGC may confuse the things...

looking inside a 3 KHz serial tone, I was puzzled by its 2 x PSK-8 rings unusual constellation: baudrate (3000 symbols/sec) and ACF (640 msec) made me think to the CIS-3000 waveform... but that PSK shape was not the expected one, so I asked my friends Karapuz and Angazu to hear their opinion and they gave me an hint: "hey, look at the amplitude of the signal!".
That's right: highlighting a single chunk of signal and selecting the SA wave form-module, is visible an amplitude variation, possibly due to fading, that in turn causes a sort of inter-symbol distortion in the phase plane and then the optical effetct of the two concentric PSK-8 rings. My wrong because, just in case, before I had to ran the wave-form module. Same conclusions if I had increased the printing delay in the phase plane as an instant-replay.
Well, good to know... especially if tinkering with AGC.
the sonogram
the two PSK-8 rings...
...and its clarification

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