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Re: Inaudible noise on telephone lines...
It does say here: http://www.digitimer.com/research/quest/
that they eliminate 50/60Hz noise from the signal which would seem to be
what my problem is...?
Thanks,
Andy.
----- Original Message -----
From: Alancc
To: ukha_d@xxxxxxx
Sent: Sunday, March 14, 2004 8:09 PM
Subject: Re: [ukha_d] Inaudible noise on telephone lines...
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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>
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