RE: low-quality cctv audio over cat5

["Keith Doxey" <ukha@xxxxxxxxxxx>]

Hi John

> 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
the
> house - wow, I'm impressed! They may be a bit over-the-top for this
use
> though but it is an option.
>

Glad you like the quality :-)


> I've got the video going over coax fine now, and I guess I've got
> nothing to lose trying to solder something direct, it's not an
> incredible long run.
>

Sending bi-directional audio over CAT5 as an unbalanced signal may result
in
crosstalk between the two channels which could end up as a horrible
feedback, it is also possible that it may pick up some hum. If this proves
to be a problem then the circuit described below should do the trick

A low cost option is to buy two "Ground Loop Isolator" units as
sold by car
accessory shops and Maplin etc. These are essentially two small
transformers
in a plastic box (or passive baluns). They have stereo phono leads coming
out of each end. You would need to buy two of these and wire up as shown
below

RC = Red Plug Centre Conductor
RO = Red Plug Outer Conductor
WC = White Plug Centre Conductor
WO = White Plug Outer Conductor

One end          Balun 1                  CAT5                  Balun 2
Other End

SendAudio-----RC-------B----RC-------BLUE/White-------RC-----B----RC----
-RecvAudio
Gnd---------------RO------A----RO-------WHITE/Blue--------RO----A----RO-
------Gnd
L
L
RecvAudio-----WC------U----WC---ORANGE/White-----WC- --U----WC-----SendA
udio
Gnd---------------WO-----N----WO----WHITE/Orange-----WO----N----WO-----G
nd

It is important that the outer of the plugs connected to the CAT5 cable are
isolated from each other because if they are in contact it will defeat the
balancing by giving a common reference to the two circuits.

Ironically, the Mk1 KAT5 units used the same PCB in the transmitter and
receiver (just different component locations were populated) and there were
actually three types of units available Transmitter (TX), Receiver (RX) and
VideoConferencing (VC) which was a unit with bidirectional audio and video
prinarily intended for video conferencing links and door intercom systems.

I say, ironically because no-one actually wanted one and now the new PCB's
can only be built as transmitter or receiver as they use different PCB.
Using a set of VC units would have enabled the video to go over the CAT5 as
well. If there is sufficient interest in a VC unit then I may produce some.

Regards

Keith