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-
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