[asterisk-users] Noise on FXS ports (Sangoma)

[John Novack]

Stephen Bosch wrote:
> John Novack wrote:
>   
>
> I don't know what configuration changes I would make to solve this. My gut feeling is that it's an electrical problem somewhere within the system, but perhaps I'm reaching for that too soon; in any case, I wouldn't know where to start even if we accept that it is an electrical problem.
>
> Is a dirty ground not a possibility?
>   
The FXS port connections normally aren't grounded, so that is doubtful. 
False grounds will usually appear as a hum at the frequency of the power 
line or double that. 50/60 Hz or 100/120Hz. This is much closer to a 
white noise.  The ground hum mentioned in earlier postings is usually 
caused by a ground loop being set up on a PSTN line to the CO. At the CO 
one side of the line is at ground, usually the + side, and in many 
systems battery and ground were fed through a split coil relay or 
inductor with battery and ground fed through the center, and the line on 
the two outside terminals, schematically speaking.  Both of these wires 
then need to be free of any ground all the way to the subscriber, or a 
ground loop would exist with the potential difference being heard as a 
hum. The longer the loop and the lower the resistance the ground, the 
louder the hum Think of a PSTN line as a 600 ohm balanced audio circuit 
but with battery on the loop for supervision.
In your case, from listening to the recording, it really seems as if it 
is being generated within the card. To be sure, if you haven't already, 
connect to the FXS port directly from a telephone with one of the 
Sangoma provided cables that adapt the 4p modular handset jack to a 6 p 
telephone jack. That would certainly eliminate ANY external source.

I confirmed that the card in a machine with out the Sangoma drivers 
running would result in a card without battery, so you really shouldn't 
hear anything. Stopping Asterisk removed dial tone, but with wanrouter 
running the result is silent battery. The only noise I hear is a VERY 
LOW pickup that seems to be coming from the monitor vertical scan. 
Nothing resembling your hiss.
I assume you don't have additional hardware to try, which makes 
troubleshooting even more difficult.
You may want to see if Sangoma will advance replace the needed parts.

Good luck

John Novack

> Is there a way to test this card in another server without having to
> install Asterisk on it? I want to see if the noise is coming off the PCI
> bus.
>
> -Stephen-
>
> _______________________________________________
> --Bandwidth and Colocation provided by Easynews.com --
>
> asterisk-users mailing list
> To UNSUBSCRIBE or update options visit:
>    http://lists.digium.com/mailman/listinfo/asterisk-users
>
>