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Raspberry Pi tone on audio from node

Lonney [KL3NO]
 

Hi all, after converting my node to a Raspberry Pi the audio from the node (into the link radio and being transmitted locally) has a loud 1kHz (or so) tone on all audio, - node enabled on bootup, connection and disconnection wave files, my own audio back from the echo reflector.

If I use bin/key to key the PTT, the tone is not present, if I hold the PTT button the link radio the tone is not present.

Here's a video demonstrating this https://youtu.be/i0NrnVURuxk

If I talk into the echo reflector my audio is returned mixed in with the tone, same with node enabled, connect/disconnect audio etc.

- Lonney
KL3NO
Node 7441

David Cameron - IRLP
 

Sounds like a ground loop with the sound card. What sound are are you using?

How is your audio wired from the USB sound card to the radio?

It seems to only make the tone when a sound is being played.

David Cameron

On 25/02/2020 5:08 p.m., Lonney [KL3NO] via Groups.Io wrote:
Hi all, after converting my node to a Raspberry Pi the audio from the node (into the link radio and being transmitted locally) has a loud 1kHz (or so) tone on all audio, - node enabled on bootup, connection and disconnection wave files, my own audio back from the echo reflector.

If I use bin/key to key the PTT, the tone is not present, if I hold the PTT button the link radio the tone is not present.

Here's a video demonstrating this https://youtu.be/i0NrnVURuxk

If I talk into the echo reflector my audio is returned mixed in with the tone, same with node enabled, connect/disconnect audio etc.

- Lonney
KL3NO
Node 7441

Teton Amateur Radio Repeater Association (TARRA)
 

I tried the link you provided in your email. The audio is so low, couldn't tell anything.

Mick - W7CAT
Node 3464


----- Original Message -----
From: "Lonney [KL3NO] via Groups.Io"
To: IRLP@irlp.groups.io
Sent: Tuesday, February 25, 2020 06:08:44 PM
Subject: [IRLP] Raspberry Pi tone on audio from node

> Hi all, after converting my node to a Raspberry Pi the audio from the node (into the link radio and being transmitted locally) has a loud 1kHz (or so) tone on all audio, - node enabled on bootup, connection and disconnection wave files, my own audio back from the echo reflector.
>
> If I use bin/key to key the PTT, the tone is not present, if I hold the PTT button the link radio the tone is not present.
>
> Here's a video demonstrating this https://youtu.be/i0NrnVURuxk ( https://youtu.be/i0NrnVURuxk )
>
> If I talk into the echo reflector my audio is returned mixed in with the tone, same with node enabled, connect/disconnect audio etc.
>
> - Lonney
> KL3NO
> Node 7441
>
>
>
>
--

 

0

Lonney [KL3NO]
 
Edited

Hi David, thanks for the reply.

C-Media 119, in alsamixer it shows as C-Media USB Audio Device.

There is only one ground connection via the speaker out (shield) from the link radio to mic in on the card.

Link radio is Baofeng - I have a DC blocking cap on the audio out from the radio, and another on the mic ground (which also doubles as the PTT on these). I had used the same Baofeng radio a few years ago with an HP thin client before I rebuilt it with a Dell desktop and an Alinco, now I want to go back to something small and portable.

I'm wanting to suspect the USB sound card, its not new. Short of any other ideas I might order a new one to rule that out since they're fairly cheap.

edit: I just tested USB sound card on a laptop with earphones, and audio out is perfectly fine.

- Lonney

David Cameron - IRLP
 

That does not negate a ground loop.... Explain how the mic ground acts as a PTT?!

I would try with the Alinco and see if the problem follows the sound card. To me, it sounds like an interfacing issue with ground loops.

Dave Cameron

On 25/02/2020 6:13 p.m., Lonney [KL3NO] via Groups.Io wrote:

[Edited Message Follows]

Hi David, thanks for the reply.

C-Media 119, in alsamixer it shows as C-Media USB Audio Device.

There is only one ground connection via the speaker out (shield) from the link radio to mic in on the card.

Link radio is Baofeng - I have a DC blocking cap on the audio out from the radio, and another on the mic ground (which also doubles as the PTT on these). I had used the same Baofeng radio a few years ago with an HP thin client before I rebuilt it with a Dell desktop and an Alinco, now I want to go back to something small and portable.

I'm wanting to suspect the USB sound card, its not new. Short of any other ideas I might order a new one to rule that out since they're fairly cheap.

edit: I just tested USB sound card on a laptop with earphones, and audio out is perfectly fine.

- Lonney

Lonney [KL3NO]
 

Hi David,

Correct, I snipped the shield connection on the mic side once I realized that it was redundant and would create a ground loop, it also mode no difference. Image on this page shows the Baofeng speaker/mike connections - http://www.ka1mzy.com/RPI-IRLP-SETUP.html

Anyhow, you're correct :-) it is a ground loop issue - I tracked the problem down, the ground loop issue is between the 12V supply to the Baofeng with battery eliminator and the Raspberry Pi supply (I'm guessing). Probably the former that has the issue as its a cheap 3A switch mode brick I picked up somewhere along the way - I had used it to power the thin client and the Baofeng (via a battery eliminator) together previously with out issue. Once I swapped that out with a charged battery for the Baofeng, problem gone!

Thanks for your help David, much appreciated!

This will turn out to be a neat little setup, I've used a Pi case intended to fit a GPIO tophat, and found I was able to fit the IRLP board in there by removing metal part of the DB25 and filing down the edge on the plastic part of the DB25, the DB9 I was able to mount in the other end where it just clears the CPU heatsink, the IRLP board happily sits in there with the DB25 and DB9 separating the board from the Pi board in the bottom of the case.

- Lonney