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Re: Inaudible noise on telephone lines...
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
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