I have a co-ax cable coming from my aerial and I have two Micromark
cctv cameras that feed into a modulator which outputs at channel 38.
What I would like to do is get the cctv feed up to the loft so it can
then be split around the various TVs in the house so I can view the
cctv output on all of them. The modulator output channel is away from
any of the aerial TV output channels.

Is there anyway of economically combining two coax cables (one from the
aerial and the other from the modulator) which would then go into the
booster to be sent to each of the other TVs?

I know I could run both of the Din cables up to the loft and put the
cctv control unit and modulator there but it would be easier if I could
take the signal up via a single coax cable which would allow the
control unit to be accessible.

Help greatly appreciated

David

In article . com,
"david" writes:
I have a co-ax cable coming from my aerial and I have two Micromark
cctv cameras that feed into a modulator which outputs at channel 38.
What I would like to do is get the cctv feed up to the loft so it can
then be split around the various TVs in the house so I can view the
cctv output on all of them. The modulator output channel is away from
any of the aerial TV output channels.

Is there anyway of economically combining two coax cables (one from the
aerial and the other from the modulator) which would then go into the
booster to be sent to each of the other TVs?

Use a passive splitter. They work in reverse as a combiner too.
They are lossy, so if your aerial signal is very weak, the addition
of a splitter might make a noticable difference.

You might also need to severely attenuate the output of the
modulator, as it's signal is likely to be orders of magnitude
larger than that from the aerial, and it could saturate the
input stage of the booster rendering the aerial signal unusable.
Try it without attenuators first, but don't be surprised if you
need to buy some.

--
Andrew Gabriel

Thanks but the aerial signal is, at times, very weak and so I don't
think this would work - but thanks for trying.

David

Andrew Gabriel wrote:
In article . com,
"david" writes:

I have a co-ax cable coming from my aerial and I have two Micromark
cctv cameras that feed into a modulator which outputs at channel 38.
What I would like to do is get the cctv feed up to the loft so it can
then be split around the various TVs in the house so I can view the
cctv output on all of them. The modulator output channel is away from
any of the aerial TV output channels.

Is there anyway of economically combining two coax cables (one from the
aerial and the other from the modulator) which would then go into the
booster to be sent to each of the other TVs?


Use a passive splitter. They work in reverse as a combiner too.
They are lossy, so if your aerial signal is very weak, the addition
of a splitter might make a noticable difference.

You might also need to severely attenuate the output of the
modulator, as it's signal is likely to be orders of magnitude
larger than that from the aerial, and it could saturate the
input stage of the booster rendering the aerial signal unusable.
Try it without attenuators first, but don't be surprised if you
need to buy some.

The OP could use frequency selective combiner/splitters. The advantage there
is that the insertion loss at the specified frequency ranges on the respective
legs is very low (typically about 1dB)

For instance I use a Group A/E combiner (21-33/37-68) to combine the outputs
from my DTT and Sky boxes on UHF Chs 22 and 25, with aerial signals UHF Chs
39-66.

--
Mark
Please replace invalid and invalid with gmx and net to reply.

david wrote:

Thanks but the aerial signal is, at times, very weak and so I don't
think this would work - but thanks for trying.

How is your amplification and distribution done? With a combined
amp/splitter or with an amp followed by a passive splitter?

If the latter, then you can do the combination between amp and splitter
rather than at the input.

If the former, then use a quality low loss inductive combiner and
attenuate the level of the modulator to be in the same range as the
aerial signal level before the combiner. Then feed the combined signal
to the distribution amp.

See:

http://cpc.farnell.com/jsp/endecaSea...=AP01305&N=411

Attenuators are available in a good range of values from 3 to 18dB:

http://cpc.farnell.com/jsp/endecaSea...U=AP18DB&N=411


--
Cheers,

John.

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david wrote:
Thanks but the aerial signal is, at times, very weak and so I don't
think this would work - but thanks for trying.

David


I imagine then there is already a multi-output preamp in the loft to
distribute the weak TV signal.
Option 1. get a second preamp for the antenna and combine the CCTV
signal with the boosted antenna signal at its output, using the passive
splitter someone else mentioned, so there is little or no antenna signal
loss.
Option 2. Get an aymmetric splitter, say -0.1dB (approx) & -20 dB.
This will give little loss on the -0.1 dB port. A ham radio friend
could probably knock one up for a few pence as similar devices are
regularly used for SWR indicators.
Option 3. Plug your CCTV output into an indoor TV antenna which will
act as a local radiator. Point this up toward your outdoor antenna from
inside the loft and the outdoor TV antenna should pick the signal up. I
haven't tried this, its just a wacky idea (and marginally illegal).


John

On 2 Jan 2006 08:38:56 -0800, david wrote:

Thanks but the aerial signal is, at times, very weak and so I don't
think this would work - but thanks for trying.

David

have a look at labgear. They probably do a twin input booster. Or just
boost the aerial signal and THEN use a passive combiner.