[asterisk-users] Help 60Hz Hum?

[Mark Bell]

Thanks for the tips John. I also forgot to mention the Adtran is a DC
unit.
The hum is introduced at the asterisk end. If I pull the bridge clips
and test the telco side of 66 block the line is fine. I will swap some
cards around and see what happens

> -----Original Message-----
> From: asterisk-users-bounces at lists.digium.com [mailto:asterisk-users-
> bounces at lists.digium.com] On Behalf Of John Novack
> Sent: Monday, October 08, 2007 2:59 PM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: Re: [asterisk-users] Help 60Hz Hum?
> 
> 
> 
> Mark Bell wrote:
> >
> > Hey guys,
> >
> > I am trying to diagnose a hum in my FXO lines
> >
> > I am using an Adtran 750 with 8 FXO ports. I am getting a pretty bad
> > hum on the line during a call.
> >
> > I have checked the Telco side of the 66 block and there is no hum
> > there so it's my problem to fix.
> >
> Is there hum on the line ONLY when the FXO port has closed the loop?
At
> the demarc? When the buttset closes the loop?
> Or is the hum introduced on the Asterisk end?
> All of the FXS ports clean and clear?
> Are you sure it is 60 Hz and not 120 Hz?
> Longitudinal imbalance introduced by a defect in one port on the FXO
> card? All 8 ports on 2 cards?
> Remember that standard analog Central Office lines ( loop start ) are
> very much like a balanced audio line with DC superimposed for
> supervision. The DC is introduced at the CO end with one side grounded
> at the CO and the other at ( open circuit ) -48VDC, and a ground on
the
> subscriber end will introduce hum, or if low enough resistance will
keep
> the line in an off hook condition.
> Swap the Adtran cards if only on some circuits, and make sure the 750
is
> well grounded.
> 
> John Novack
> 
> --
> Dog is my co-pilot
> 
> 
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