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

[John Novack]

Since the OP said the noise was on FXS ports, Jorge's answer isn't relevant.
After listening to  a wav file of the noise, it sounds to my old ears 
like a background hiss or so called "comfort" noise, except for a couple 
of short pops which I assume to be an open microphone.

Assuming this isn't generated by the POTS set connected to the port, I 
guess you'll have to dig into the configuration.
Some POTS sets generate a similar though more erratic noise, caused by 
carbon transmitters and defective varistors in the network, but that is 
ancient history.
More modern POTS sets with electret transmitters could certainly 
generate a similar noise.
I am assuming that several different sets have been tried with similar 
results.

My experience with the Sangoma A200, and in fact Digium 400 and Adtran 
channel bank FXS circuits all are very quiet, so this is a bit of a puzzle.

John Novack


Jorge Mendoza wrote:
> Stephen Bosch wrote:
>> Hi, Jorge:
>>
>> Jorge Mendoza wrote:
>>  
>>>>         
>>> Never experienced with FXS modules on a PC with  Asterisk. However we
>>> have experienced that kind of problems on legacy PBX without a good
>>> ground. If you replace the system with a analogue set and have not
>>> noise, then a ground current is generated in your system, probably
>>> originated at FXO side. Have you tested the PC isolated, with not lines
>>> and not switches? just the FXS calling the voicemail?
>>>     
>>
>> No, I haven't gone that far yet, but it might be worth trying.
>>
>> One question I have: if this turned out to be the cause, what could I do
>> to clean up the ground? There are so many elements -- the power supply
>> ground, the telephone lines, the network cable ground, etc.
>>
>> -Stephen-
>>   
> Stephen,
>
> Good question. Finding ground problems is an art.
> First thing I should do: measuring your ground with respect of CO 
> ground. With a voltmeter between the tip wire of your CO line (0 VDC ) 
> and your local ground, voltage should be less than 5 VDC.
>
> Jorge
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