Hi Paul,
thanks for the analysis and the tutorial :-)
Am 09.07.2017 07:46, schrieb Paul Nicholson:
What signal voltage does your DDS put into the Octo?
It was at 10 mV +- 0.5 mV.
What input gain is alsamixer set to?
All channels set to 49/100, this is +6.5 dB gain.
Am 08.07.2017 19:38, schrieb Paul Nicholson:
We can just see a slight change to the ch1 amplitude
which lasts about 100mS.
OK, so no loss of samples, rather an AM component. That's not so
dramatic. Anyway, let's find the problem.
Likely to be an EMC effect. I will have a look on the pcb and will
eventually re-solder some pins.
It would also be useful to stream CH1 and CH2 via the LAN so i can
watch it into SpecLab in real time. Then i could use some cooling spray
to seach for bad solder contact. Often it also helps just to touch the
contacts with the finger and see for any differences. It started my
radio 'carrer' that way ;-) : In 1993, when i was 17 yrs old, a friend
donated me a damaged CB-transmitter. I simply touched the pcb
everywhere until i found a region where the noise started to sound
different. Suddenly i heared some people talking!!!!! I replaced a
capacitor and it worked again...
So far i didn't manage to send a stream over the network to receive it
on my windows PC in SpecLab. Maybe you have an idea? :-) I saw the
notes on the vlfrx tools documentation site of course, but didn't spend
enough time on that so far it seems.
Just shows a steady phase drift, we're not quite on
frequency here
with this recording
This is due to my undisciplined DDS VFO.
- did it go through vttime?
Unintentionally not. vtcard sends to a buffer @raw, vttime takes from
@raw and sends to @locked. I disabled vttime for an earlier test and
put vtresample to @raw instead of @locked. Forgot to correct that for
the test.
But it doesn't matter for getting the glitches.
Curious. Signal goes up, background noise drops. I wonder
if
there is a dodgy input capacitor or dry joint. Not sure about
that explanation, it would be odd to see the same on more than
one channel.
Right. I had the same thought some days back, that's why i re-build the
original audio input interface. So obviously that's not the reason
since it happens on both constructions.
Wonder if the effect occurs at the same time on ch1 and
say ch4?
Or instead the effect is independent on the effected channels.
>From the recent monitoring of all 6 channels (3 pairs) it looks like it
is independent.
So far we can say that it is just a small AM component, that's not so
dramatic. Anyway i will continue to search for the reason...
73, Stefan
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