Return to KLUBNL.PL main page

[Top] [All Lists]

Re: LF: Octo-soundcard for the Raspi, another question

To: [email protected]
Subject: Re: LF: Octo-soundcard for the Raspi, another question
From: DK7FC <[email protected]>
Date: Sun, 09 Jul 2017 12:43:48 +0200
In-reply-to: <[email protected]>
References: <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]>
Reply-to: [email protected]
Sender: [email protected]
User-agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv: Gecko/20100227 Thunderbird/3.0.3
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

<Prev in Thread] Current Thread [Next in Thread>