RE: [KAT5] Question from non-expert

["Keith Doxey" <kat5users@xxxxxxxxxxx>]

Hi Mark/Tony,

If two terminated units are connected to a single transmitter the
termination resistance is halved and so is the signal level which will lead
to a dark picture with strong colour and possibly instability as well.

If you run a long unterminated stub then the signal will hit the end of the
cable and bounce back towards the transmitter. This leads to ghosting and
instability.

The video pairs are terminated by 100R resistors which matches the
characteristic impedance of CAT5 cable. The audio pairs are terminated by
620R resistors.

If the value of these was doubled to 200R and 1K2 respectively then
connecting two terminated units would give the correct signal levels but
the
cable would NOT be terminated correctly and may still give ghosting but to
a
lesser extent than having a long unterminated stub.

If you want to try this I can supply instructions on how to do it. It only
involves fitting 4 resistors to the unterminated unit and changing the
existing 4 resistors in the terminated unit. After this was done you would
have to keep both "half terminated" units connected at all times.
I cant
guarantee what the picture would be like as the length of the cable also
has
an effect, the longer the cable the worse the reflections. If the results
were unacceptable you could easily revert to the proper termination
resistors.

Hope that helps

Keith

> -----Original Message-----
> From: Tony Butler [mailto:lists@xxxxxxx]
>
> Keith would be the one to ask about this - you *might* be able to get
away
> with this by changing the values of the terminating resistors, either
> doubling or halving them I (I can never remember which way around
> it should
> be when doing things in parallel - usually the opposite of what I
think it
> is though!)
> Depends on if the TX unit needs to "see" a total of XX ohms
> resistance from
> the other end, or if there needs to be XX ohms at each terminator.
>
> As I say, Keith would be the real man to tell you, but he is out of
action
> for a little while....
>
> Cheers,
>
> T.
>
> > -----Original Message-----
> > From: erstwing_challenge [mailto:mark@xxxxxxx]
> >
> > Pardon me if this is a silly question, but I would be
> > grateful to know the answer. A bit of background:
> >
> > I have been using 3 receivers together with a single
> > transmitter for some time. I have used the patchable system
> > configuration. I have recently added a fourth receiver in my
> > kitchen that has only a single
> > CAT5 outlet, so I moved the terminated receiver here. In the
> > bedroom where I did have the terminated receiver there is a
> > second CAT5 outlet at the other end of the room, so I am
> > currently using a long patch lead to reach it.
> >
> > What I would like to know is whether there is any way that I
> > could use 2 terminated receivers in the same circuit (by some
> > combination of splitters or whatever). It would save me
> > trailing a patch lead. If not I will eventually run another
> > CAT5 from the loft.
> >
> > Thanks
> >
> > Mark Fulford
> >



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