Video ??Multiplexer??

[mac.calder]

I have a gig comming into my venue soon which will require TV's in about 8 locations, each able to flick through 8 to 20 channels (depending on the day and the budget) on a whim. Obviously, running 20 lines to a switch in each room is out of the question, so general consensus is we need to do it the way things are done in real life with TV - using the TV's inbuilt tuner and RF.

 

We have the coax left over from a conference a few years ago, however the rest of our infrastructure was sold, and the person who specced and purchased the equiptment has left. So what I need to know, is what is at the start of the chain.

 

Ie we have video sources -> X -> Coaxial cable/Spliiters/etc -> TV Tuner, what is X called, and where would I get one? (and what is the damage bill likely to be)

 

Any help will be greatly appreciated

[David Duffy]

Sounds like all you need is a bunch of RF modulators. Cypress make some nice PLL ones. Just punch in the channel, loop 'em all together and that should be it.

[dosxuk]

We use a pair of old video recorders for this purpose.

[Pete McCrea]

As far as I'm aware VCRs are great for De-Modulating the RF to video, but not the other way- video to RF, which is what I believe the OP is after. You'll need a Modulator, and as mentioned above daisy chain them together. I did a brief bit of work recently trying to find a De-Mod, but failed. whilst on that quest I didn't spot any Multi Channel Modulators. CPC and RS had some options that may be worth a Google if for nothing mroe than info.

[endorphin]

As far as I'm aware VCRs are great for De-Modulating the RF to video, but not the other way- video to RF,

 

some of the older ones (pre-scart) and possibly some newer used the multiplexing to RF to get the image on to the TV via its RF in. The more expensive ones sometimes had a aux in which can be used. Get a few tune them to different frequencies and have an RF distribution and you've got a relatively cheap system.

 

Edd

[paulears]

The only thing to watch for is that cheap modulators are rather wide - double sideband, rather than the usual vestigial sideband - meaning that they have to be spaced a fair way apart or they do tend to make a mess of each other. Your bottom limit of 8 channels sould be ok, but you aren't going to fit anywhere near 20 in!

[peternewman]

I've also succeeded in getting an old analogue satellite set top box to work as a modulator, connecting the source to the external decoder scart and then telling it to use an external decoder on that channel, so that could be another possible option. I think this has been covered on here before, although only in general and probably not for people wanting multiple modulators, so a search may be beneficial.

[Dave]

What you are trying to do is very similar to a standard technique called SMATV which is used for distributing multiple satellite channels around a building via UHF.

 

Basically you have an array of satellite receivers that feed external VSB UHF modulators. The outputs of these modulators are combined (possibly after filtering) and the resulting multi-channel signal goes into a UHF distribution network. This is exactly what you need, substituting your own video sources for the receivers.

 

But it's an area of technology I've never really worked in, so I'm not familiar with equipment makes and design factors etc.

 

However, whilst recently researching something vaguely related (Integrated Reception Systems), I came across an installer's web site with some nice photos of large SMATV systems - click here and here.

 

Here's an example image showing the modulators:

 

http://www.aerialview.co.uk/My_Pics/CDI/VSB_Mods_in_19inch_Rack.jpg

 

If anyone can identify the equipment used (in this and the other photos on the site), I'd be interested to know.

[Andrew C]

Where's Brian when you need him? ;)

 

I'm looking at a similar (but permanent) set up, and he recommended these folk for part of the system. Not got any further yet, but they do what you need. Oh, be warned, the catalogue is a series of pdfs and may clog a dial-up.

[boatman]

Try MGA Communications for this type of system. They do systems for Housing Associations, Hotels and the like.

[paulears]

I made a promo video on one of these once - There were delays in getting the product delivered, which seemed odd until it did arrive - in a securicor armoured vehicle. The thing was gold plated - and for an Arab Prince from the Gulf. All the time we were spinning it around and moving cards in and out a big bloke in a uniform watched every move. Gold plated, to live in a electronics rack!

[dbuckley]

Yep, SMATV modulators is what is needed, the ones I last used were (I think) Philips, with four modulators per 1u box.

 

SMATV works pretty much like analoge CATV, but on a reduced scale, using the same bits and bobs.

 

To save me a bunch of typing - is your wiring star or daisy chain?

 

Its a pity you are in Oz, all this stuff is avalilable trivially easiliy from CPC in the UK :D

 

The other thing you need to watch out for is intermod distortion, same bogey as wireless mics, which (assuming Oz uses UHF TV similar to the UK) for 20 channels may be a squeeze, but 8 is ok. See information on taboo TV channels.

[Dave]

The other thing you need to watch out for is intermod distortion, same bogey as wireless mics, which (assuming Oz uses UHF TV similar to the UK) for 20 channels may be a squeeze, but 8 is ok. See information on taboo TV channels.

 

David, the web site I linked to in my previous post had pictures of up to 40 channel SMATV systems! I'm aware of the IMD issue, but I wonder if it's like radio mics - dearer ones have better filtering and you can have more channels operational. Any ideas?

[henny]

howabout thinnking the other way round, why not use a 16x8 way Matrix at the sorce and just run a comp and audio out to each room and an RS232 control back from a button pannel at the tv, or just 2 switches at the pc back to a costom controler that takes ch up/down from the tv as 2 switches and tells the Matrix what to do, the would also give you an option to remote override. you can send all the vid/audio and 2 buttons down one pice of cat5 so cableing would be easy

 

ian

[dosxuk]

I've been installing some gear that does exactly that: http://www.cabletime.com/productview.asp?s...diaStar_Compact, but does require CAT5 between boxes, rather than the UHF the OP said he had plenty of.

 

(No idea of costs)