FreeDV and Linux

[Mike Stansberry]

Yet another question (this is quite lengthy.)
This question is directed to the Linux users of FreeDV.
I am using Linux Mint 22.1

Input To Computer From Radio:
alsa_input.usb-Burr-Brown_from_TI_USB_Audio_CODEC-00.iec958-stereo
(TI_USB_Aduio_CODEC is my IC-7200
======
Output From Computer TO Speaker/Headphone:
alsa_output.usb-Logitech_Inc_Logitech_USB_Headset_H540_00000000-00.analog-stereo
======
Input From Microphone To Computer:
alsa_input.usb-Logitech_Inc_Logitech_USB_Headset_H540_00000000-00.analog-stereo
======
Output From Computer TO Radio:
alsa_output.usb-Burr-Brown_from_TI_USB_Audio_CODEC-00.analog-stereo
======

This device:

alsa_output.usb-0d8c_USB_Sound_Device-00.analog-stereo

is connected to a small stereo amplifier outputting to 2 wall mounted
speakers.

The issue is this:  When I have the audio amplifieer turned on,
I hear the transmit audio coming through the speakers EVEN THOUGH
it is being routed properly to the IC-7200 and I have power output
on the radio.  This is quite annoying (of course I can turn off the
audio amplifier) and it keeps me from using the USB sound device,
through the audio amplifier, as the output device.  I don't want
to listen to that noise while transmitting.

I have a feeling this is a Linux related issue, not a FreeDV issue.
I'm using pulse audio with the Pulse Audio Volume Control Linux
based application.  I can't find anything in the PAVU control app
that seems to change it.  As a matter of fact, when I tried making
changes I had a hard time getting things back to where they worked.

Any Linux users out there have any ideas?

Thanks and 73, Mike, K0TER

[Peter Marks]

I have experienced this and it turned out to be RF getting in to the amplified speaker. Try reducing transmit power to zero to test this. I was powering off the speaker during transmit for a while until I overcame the problem.

I do use Ubuntu 24.04 with similar audio configuration to you. IC-7300 and Logitech USB audio dongle. Amplified speaker from the dongle. I'm not hearing the transmit signal.

Peter

VK3TPM

[Víctor J. Sánchez]

I've had a simmilar issue when I transmitted in LSB/USB instead LSB-D/USB-D (digital mode) according with my rig setting (Yaesu FT-857D, menu #038 DIG MODE = PSK31-L/PSK31-U + Yaesu SCU-17, Debian 13).

I had a heird noise through speakers simmilar to RFI issue but it hadn't such thing.

Vic EA4GRG

----

El 5/9/25 a las 3:45, Peter Marks escribió:

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[Mike Stansberry]

Interesting.  It does go away when the power is reduced to 0 (lowest setting) and slowly
increases in audio amplitude as I increase the radio's power.  It does it on any frequency.
It does this with the radio connected t a dummy load and even with the coax cable
disconnected from the radio's output.

I still don't know what might be causing it.  However, I did find a  workaround that seems
to work.  The audio amplifier uses 12 VDC power and it was hooked up to the same power
source as the radio (an Iota power supply).  I found a "wall wart" of adequate size with the
same size of pin plug for the power and tried powering the audio amp from that instead of
the power supply.  The noise is still there but at a greatly reduced level.  I can still hear it if
I turn the audio amplifier audio gain why up but that's much higher than I would use it with
FreeDV.

I heard some guys in a QSO on 40M last night and checked where the audio amp gain control
needs to be and it is much lower than when I turned it up and heard the transmit audio coming
through.  So the system is usable.

Thanks for your response and to the other Ham who also responded.

73, Mike, K0TER

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[Rick Kunath]

Mike,

It sounds like you have determined that this is RF getting into the
speakers then if I read all of the comments correctly.

Years ago when I has some limited space for antennas I had a boatload of
similar problems with RF getting into abiout everything. It drove me
nuts. I finally built up a small RF current meter that is self adjusting
and that allowed me to see where the RF hot spots were to properly apply
chokes and RF bypass capacitors to clean it all up. It's a loop coupled
meter, so no clamp on or anything and it is self adjusting. A handful of
parts and a meter movement and that's about it. If you are interested
let me know.

If you ran that along any cables, coaxes, etc, it might help to see
where the RF is getting coupled in. Outboard amplified speakers are
especially sensitive to RF. You might need to open them up and apply
some measures there.

Did you say what your antenna was?

I had originally thought this was an issue of there being a "monitor" of
the rig audio active in the sound system settings, but it does not look
like that is the case now, right?

Rick Kunath, K9AO

[Mike Stansberry]

On 9/5/25 12:02, Rick Kunath wrote:
> Mike,
>
> It sounds like you have determined that this is RF getting into the
> speakers then if I read all of the comments correctly.

Well, I don't really think so.  As I mentioned I was connected to a
dummy load when I was
testing.  I started out at minimum transmitter power and slowly dialed
it up to full 100 watts
output with the digital sound increasing coming through the audio
amplifier.  After I powered the
audio amp from a separate (from the IC-7200 supply) wall wart the sound
was greatly reduced.
It did not increase when I switch off the dummy load to the antenna. 
And it did not increase
when I increased the output power to >500 Watts through my HF amp.  The
only thing I can
think of that makes even any sense is that the increasing load on the
IC-7200 power supply
somehow affected things.  Some kind of a ground loop?

>
> Years ago when I has some limited space for antennas I had a boatload
> of similar problems with RF getting into abiout everything. It drove
> me nuts. I finally built up a small RF current meter that is self
> adjusting and that allowed me to see where the RF hot spots were to
> properly apply chokes and RF bypass capacitors to clean it all up.
> It's a loop coupled meter, so no clamp on or anything and it is self
> adjusting. A handful of parts and a meter movement and that's about
> it. If you are interested let me know.
>

Yes, I'm interested.  I've had enough issues with RF getting things that
I would like
to build such a piece of equipment.  email to k0ter...@gmail.com

> If you ran that along any cables, coaxes, etc, it might help to see
> where the RF is getting coupled in. Outboard amplified speakers are
> especially sensitive to RF. You might need to open them up and apply
> some measures there.
>
> Did you say what your antenna was?

No, I didn't but it's either a 20/15/10 tri-band trap Yagi (Cushcraft
A3S) or an 80M vee
about 37 feet at the apex.  It's fed with window line through a home
built antenna
coupler ( tuner ).  No problems, at least with CW, with a full KW output.

>
> I had originally thought this was an issue of there being a "monitor"
> of the rig audio active in the sound system settings, but it does not
> look like that is the case now, right?

Well, I'm just not sure.

>
> Rick Kunath, K9AO

Thanks for your ideas.  Food for thought.

73, Mike, K0TER