OT: multi input and output rf modulator

[Gazz]

Anyone know if such a thing exists??

i want to take the outputs of 4 camera's in my aviary, convert the composite signals to RF, send the signals down a single length of coax to the living room, where it will split to the bedroom tv as well,

then i can select either of the 4 camera's by selecting a channel on either tv,

i know i could do this with 4 single rf modulators (not sure if it'd cause problems routing 4 outputs together), but i was wondering if there is such a thing as a multi input and output one?

[NT]

outputs can be combined, impedances will reduce signal levels, but it'll probably be ok with 4 outputs.

[Mr. Benn]

You will need a 4-way RF combiner or splitter. If you tie all 4 modulator outputs together you will create an impedance mismatch which will cause reflections along the length of coax. This will result in ghosting on an analogue video signal.

Make sure the RF modulator, splitter and coax impedances are all the same (generally 75 ohms or 50 ohms).

[Gazz]

cool,, thanks for the info,

i've found someone selling 5 single modulators, they have aerial in and out sockets, i bet i'd cause all sorts of problems if i were to daisy chain them all.... i.e. first modulator's output goes to 2nd modulators input/loop thru connector, 2nd modulators output which has the 1st's signal looping through goes to 3rd mod's input, 3rd goes to 4th, which goes to the coax to the living room, where it splits to go to the bedroom....

the coax from the living room to the bedroom is to take the sky box's rf output there, i have no terrestrial antenna here.. i only watch sky, so i have the sky's loop through input free.... so if i were to feed the modulators signals to the sky box's loop through input... the powered rf output goes to the bedroom, the 2nd non powered rf output goes to the living room tv (atm it isnt connected, i use a scart lead between sky box and that tv)

does that all sound likme a recipie for disaster?

[fred]

In article , Gazz writes

Actually, no reason why you can't cascade them, cascaded tuners and modulators were the norm in everyone's living room when connecting things up before (and sometimes after) scart. A chain of four doesn't seem excessive.

Not really my bag.

[airsmoothed]

That should work after a fashion, provided you have control over the RF modulators' output frequencies so they can be spaced a few channels apart.

[NT]

If they really do have aerial inputs that could work. But al the modulators I've seen only have baseband inputs.

NT

[John Rumm]

With decent modulators (like the CYP digitally controlled one, or the proception one [1]), a cascade should be ok. Obviously you need to pick your channels carefully so as not to trample on each other or on any broadcast channels.

[1]

[airsmoothed]

The cheapskate route would be to use old VCRs as the modulators, if you've got plenty of space to waste. Don't use an even spacing between carriers, this will reduce the chances of intermods. stamping on your wanted signal as John Rumm states

[NT]

or take the modulator modules out. But it still means collecting several old VCRs

NT

[Frank Erskine]

Plenty of those about, in skips etc!