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

[Stephen Bosch]

shadowym wrote:
>  
> Every Sangoma A200 card I have ever connected to the PSTN required a rx gain
> of at least 10.  Yours is commented out which I believe would make it
> default to 0?

The noise is present on FXS ports only and is audible the moment the
receiver is lifted.

I mention this because you say "Every Sangoma A200 card I have ever
connected to the PSTN". The affected ports aren't connected to the PSTN.

> I am guessing that because the rx gain is so low the users
> are cranking up the phone volume all the way and maybe your hearing
> amplifier background noise??

Well, these are simple, analog sets. There's no amplifier or gain
control on the set. They have the traditional varistor for amplitude
balancing. If what you say is true, the varistor might be compensating
so aggressively that it's making the noise audible.

This explanation seems inadequate, though, as I don't hear this sound on
any of the SIP phones; only the analog phones connected to FXS ports.

A Sangoma engineer told me to increase the txgain, but as I mentioned,
that didn't help.

> Your should run ztmonitor and adjust your gains.

I didn't know it was appropriate to use ztmonitor with Sangoma hardware.

-Stephen-