Re: Inaudible noise on telephone lines...

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

Yep that's the earth loop hum, they break the earth loop with a transformer
rather than filter out the lower frequencies the higher frequencies of the
video signal still pass through.
Being a transformer they will not allow the DC on the telephone line to
pass
through.

Alancc
----- Original Message -----
From: "Andrew Kilgore" <amkilgore@xxxxxxx>
To: <ukha_d@xxxxxxx>
Sent: Sunday, March 14, 2004 8:14 PM
Subject: Re: [ukha_d] 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




UK Home Automation Meet 2004 - BOOK NOW!
http://www.ukha2004.com

http://www.automatedhome.co.uk
Post message: ukha_d@xxxxxxx
Subscribe:  ukha_d-subscribe@xxxxxxx
Unsubscribe:  ukha_d-unsubscribe@xxxxxxx
List owner:  ukha_d-owner@xxxxxxx