RE: low-quality cctv audio over cat5

["John Risby" <john@xxxxxxxxxxxxx>]

Thanks for that Keith - Maplin are out of ground loop isolators both
locally and online. Our new Halfords - which opened today - only had one
in stock and it was =A314.99 as opposed to Mapin's =A38.99.

Anyway, I've just found an online shop in Bolton and ordered two for
=A313.86 including delivery - Bargain (tm) !

If anyone else wants the details, please email me.

I'll let you know if I get it working ok.

John


> -----Original Message-----
> From: ukha_d@xxxxxxx [mailto:ukha_d@xxxxxxx]=20
> On Behalf Of Keith Doxey
> Sent: 03 August 2005 12:01
> To: ukha_d@xxxxxxx
> Subject: RE: [ukha_d] low-quality cctv audio over cat5
>=20
>=20
> Hi John
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> > Thanks Tim, no, I didn't get a reply other than yours!
> >
> > I've just taken delivery of some kat5 modules for sending TV
around=20
> > the house - wow, I'm impressed! They may be a bit over-the-top
for=20
> > this use though but it is an option.
> >
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> Glad you like the quality :-)
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> > I've got the video going over coax fine now, and I guess I've
got=20
> > nothing to lose trying to solder something direct, it's not an=20
> > incredible long run.
> >
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> Sending bi-directional audio over CAT5 as an unbalanced=20
> signal may result in crosstalk between the two channels which=20
> could end up as a horrible feedback, it is also possible that=20
> it may pick up some hum. If this proves to be a problem then=20
> the circuit described below should do the trick
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> A low cost option is to buy two "Ground Loop Isolator"
units=20
> as sold by car accessory shops and Maplin etc. These are=20
> essentially two small transformers in a plastic box (or=20
> passive baluns). They have stereo phono leads coming out of=20
> each end. You would need to buy two of these and wire up as=20
> shown below
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> RC =3D Red Plug Centre Conductor
> RO =3D Red Plug Outer Conductor
> WC =3D White Plug Centre Conductor
> WO =3D White Plug Outer Conductor
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> One end          Balun 1                  CAT5               =
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>   Balun 2
> Other End
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> SendAudio-----RC-------B----RC-------BLUE/White-------RC----
> -B----RC
> SendAudio-----RC-------B----
> -RecvAudio
> Gnd---------------RO------A----RO-------WHITE/Blue--------RO
> ----A---
> Gnd---------------RO------A-RO-
> ------Gnd
>                                 L
> L
> RecvAudio-----WC------U----WC---ORANGE/White-----WC-=20
> RecvAudio-----WC------U--U----WC-----SendA
> udio
> Gnd---------------WO-----N----WO----WHITE/Orange-----WO----
> N----WO--
> Gnd---------------WO-----N---G
> nd
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> It is important that the outer of the plugs connected to the=20
> CAT5 cable are isolated from each other because if they are=20
> in contact it will defeat the balancing by giving a common=20
> reference to the two circuits.
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> Ironically, the Mk1 KAT5 units used the same PCB in the=20
> transmitter and receiver (just different component locations=20
> were populated) and there were actually three types of units=20
> available Transmitter (TX), Receiver (RX) and=20
> VideoConferencing (VC) which was a unit with bidirectional=20
> audio and video prinarily intended for video conferencing=20
> links and door intercom systems.
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> I say, ironically because no-one actually wanted one and now=20
> the new PCB's can only be built as transmitter or receiver as=20
> they use different PCB. Using a set of VC units would have=20
> enabled the video to go over the CAT5 as well. If there is=20
> sufficient interest in a VC unit then I may produce some.
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> Regards
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> Keith
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