[hpsdr] WSJT VAC, ALC and PowerSDR mRX PS

[John Laur]

I will admit to making this elementary mistake myself, so my apologies if
you have already looked at this. It seems you may somehow have routed RX
audio back to the TX. The easiest way to make this mistake is to use only
one virtual cable instead of two. The receive audio continues to playback
for a very brief moment after TX is triggered due to the various DSP
buffers and the VAC delay. Unlike a regular sound card, VAC is continuously
copying each virtual cable's input to its output. Since VAC will mix
multiple inputs to the same cable this sort of thing can result. Make sure
you have Cable #1 configured as PowerSDR output and WSJT input and Cable #2
configured as PowerSDR Input and WSJT Output.

A very long time ago there was a different problem which caused the same
sort of behavior before the T/R transitions were reworked in PowerSDR, but
if you are on the latest releases of software and firmware this should not
be your problem.

73, John KF5SAB.

On Sat, Oct 11, 2014 at 4:07 PM, Conrad Farlow <conrad at g0ruz.com> wrote:

> ***** High Performance Software Defined Radio Discussion List *****
>
> I am using an ANAN-10 with the latest version of PowerSDR mRx PS. I have
> VAC working well with WSJT but I get a burst of noise just before WSJT
> starts generating audio. It is 20dB below the modulated audio and I suspect
> that is due to some kind of expander action on the ALC. I am driving a
> transverter and have only 500mW output to do so. My TX is very clean but is
> there any way of getting rid of this, in fact turning the TX ALC off
> altogether? I don't need it as the audio level is tightly controlled and I
> have a the TX gain set at around 75dB. There is no way that I am going to
> overdrive anything.
> --
>
> __________________________________________________
>
> 73
>
> Conrad G0RUZ IO93FR
>
>
> North Wakefield Radio Club
>
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