Combining Co-ax cables

[david]

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

[Andrew Gabriel]

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.

[david]

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

David

[Mark Carver]

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.

[John Rumm]

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:

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

[john]

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

[The Natural Philosopher]

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