Hello Markus,
Am 09.07.2017 11:34, schrieb Markus Vester:
First
I thought it might be flicker noise on the ADC reference voltage but
why should it affect only three of six channels?
Right.
With
USB soundcards, the data packets are usually sent with 1 ms repeat
rate, and we have sometimes seen an artifact consisting of weak 1 kHz
spaced spectral lines. I do not know about the transfer protocol of the
Octo soundcard which is connected to the RasPi interface pins. In case
the packets are organized similarly, we might experience the
same problem, so 1 kHz or 0.5 kHz might have been just an unlucky
choice for the test signal frequency. Perhaps you could try again at
some odd frequency?
That's a good point.
Also a test at higher amplitude (e.g. -20 dB FS) would tell us whether
it is a multiplicative (ADC scaling) or additive (EMC) error..
I will use different signal levels and will report in a separate email.
The
warm summer is not a good time to bury oneself in the shack ;-)
Warm? It is HOT!!! I can't stay outside in the sun during the midday
time. The sun is out for 16 hours per day now, so i can easily afford
to spend 4...6 hours in the shack/office in the midday time. Yesterday
i have been on the tree until 21:20 local time. A great pleasure. BTW
it was the 95th time that i climbed the tree :-)
I shut down the Raspi to take a clone of the SD card. No i think about
installing vlfrx tools there, remotely, while sitting in the cool
office :-)
73, Stefan
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