[Asterisk-Users] Woodpeckers Revisited

[Rich Adamson]

Mike,

> The Qwest HQ noise team assures me that my lines are within spec.  Sure 
> enough, when I listen on the test set the lines are clear.
> 
> The lines terminate at an Adtran 750 channel bank on my * system.  When 
> I reconnect the lines to the channel bank and make a call, I get the 
> hum/buz noise. I have replaced every Adtran component (even the 
> chassis), but the hum/buz stays with the lines.
> 
>  From the CO we have a digital fibre optic system which terminates at a 
> neighborhood cabinet.  From there, analog copper cables distribute 
> service to the houses.  I'm suspecting that the digital-to-analog 
> process doesn't give a smooth analog signal but rather a "stair-stepped" 
> signal, with each step 1/8000 sec in duration (I wish I had a 'scope to 
> confirm this.)  The human ear can't hear this stair-stepped signal, so 
> it's ok for POTS use.
> 
> However, when I put this stair-stepped signal to the channel bank, it 
> converts it back into a digital signal.  I'm thinking that, because it's 
> not a smoothed signal, the analog-to-digital process injects hum and 
> buz.  Does _anyone_ have more information on this?

As I've mentioned to you in previous posts, I use to work as a telephone
engineer for 20+ years and did a lot of noise measurements, etc, over the
years. Your stair-stepped signal issue is not the problem for sure. If
you could put a scope on the line, you wouldn't see jagged edges at all,
however you "might" see the real source of the problem. In order to do
that, you'd have to use a dual-input oscilloscope that has the capabilities
of displaying the difference between those two inputs (differential mode),
and have an input sensitivity that would go down to something on  the order
of .1 volts/div or so.

The Qwest folks would be doing about the equivalent as the scope, but with
a noise meter that typically is filtered to look only at the 20hz to 4000hz
range (or something like that). Those devices will generally go down to
about -90 db or so, and they also look for imbalances betwee tip & ring
(eg, water in the cable). The meter should be far more sensitive then the
average person's ears.

If they obtained those measurements from outside your house (and they may
have disconnected the internal wiring to do that), then in all liklihood
there is something inside your house causing the imbalance & noise. If
they came inside the house with the meter and indicated things were within
spec, then something is messed up in the Adtran/asterisk area or the 
physical connections to it.

> In the meantime I've had an ISDN circuit installed so as to have digital 
> all the way to the * box.  However, I can't get the ASUSCOM ISDNLink 
> card to work with ISDN4Linux :-(

Don't know anything about this card.

Rich