Re: Inaudible noise on telephone lines...

["Alancc" <alan.cc@xxxxxxxxxxxx>]

Humbugs for CCTV are usualy isolation transformers to prevent ground loop
problems so I dont think they will help.

Alancc
----- Original Message -----
From: "Tim Fletcher" <timfletcher@xxxxxxx>
To: <ukha_d@xxxxxxx>
Sent: Sunday, March 14, 2004 6:55 PM
Subject: Re: [ukha_d] Inaudible noise on telephone lines...


> I have some tecton Humbug filters that are to filter noise from video
signals under broadly similar circs - They are BNC-BNC in-line modules but
you are welcome to one - it should be easy to try and might work!
>
> Tim.
>
>   ----- Original Message -----
>   From: Andrew Kilgore
>   To: ukha_d@xxxxxxx
>   Sent: Sunday, March 14, 2004 3:11 PM
>   Subject: [ukha_d] Inaudible noise on telephone lines...
>
>
>   Hi all,
>
>   After much tinkering with two HV Phone/Serial add-on units, I've had
to
face
>   up to the fact that I have sufficient noise on the phone line to
prevent
>   both versions of the device from working properly. Version I unit
could
>   detect on/off hook status correctly but had problems with detecting
ringing
>   and DTMF tones. Version II unit (with the newest chip from CSI) has
no
>   problems with DTMF or ring detection but is unable to detect on/off
hook
>   status :o(
>
>   So, two questions:
>
>   1. Does anyone know of any type of filter I can try to eliminate the
noise.
>   Having a cable modem I don't know too much about ADSL etc. but I do
know
>   that it usuall requires a microfilter. Any similar devicethat I
could
>   try...?
>
>   2. Failing this, is there any point in ringing my provider (NTL),
informing
>   them of my problem and asking them to help...? (Long shot I know
;o)).
What
>   would 'one' say to stand the best chance of getting something
done...?
>
>   Below is a snippet from the csi website which describes the cause of
the
>   problem
>
>   =======================================================
>   About 5% of users experience this problem. It is due to excessive
noise
on
>   your home's phone line. This isn't audible noise - it's 60Hz AC
"common
>   mode" noise. This means the noise appears on both phone line
wires
equally,
>   and the noise is relative to earth ground. Because most phones only
care
>   about the relative voltage between the two wires, they aren't
affected
by
>   this noise, and you won't normally even hear it. The problem usually
occurs
>   when the phone lines run parallel to high-voltage AC power lines for
several
>   miles or more. This high voltage can induce noise onto the phone
lines.
>   Unfortunately, there is nothing we are aware of that a homeowner can
do
to
>   eliminate this noise.
>   If the noise goes above 10 or 15 volts AC, the phone interface chip
in
the
>   version-2 phone devices may become unable to determine whether the
phone
is
>   on or off hook. This will also cause the phone device's green LED to
show
>   the incorrect conditions. With the version-1 devices, the noise
would
have a
>   different effect. Hook status would work fine, but touchtone (DTMF)
and
>   caller ID detection could be degraded. We thought the newer
version-2
>   devices would be immune to the noise, but they aren't (although they
are
>   less susceptible than the version-1 devices that many users beta
tested.
>
>   =======================================================
>
>   Many thanks,
>   Andy.
>
>
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