VGA to Composite Converter

[russellhltn]

If the only reason to run the cable is for a overflow projector, and you're running a cable though the chapel, consider using something other than composite. If you're feeding a webcast or other rooms, then you may have to make a sacrifice in quality to get the signal from point A to point B.

[craiggsmith]

We have two jacks at the podium, one is RCA composite video that we use to show satellite broadcasts, and the other is F connector RF video and we haven't used it in years. We do have a jack in the overflow that we use for the camera input for webcasts, but we want an input at the podium. We would probably use it often enough and I'd really like to avoid running temporary cable, especially across traffic areas and especially coax that doesn't want to lay flat. We would use it mainly for the overflow projector but also occasionally for webcasts. I just haven't found any other good options.

I will try to get up there this weekend and see if I can determine if it's a direct connection or not. Not sure if it's really possible to tell though.

[Mikerowaved]

Before you decide to use it, first check to see what kind of cable it is. Unscrew the wall plate with the F-connector and pull enough coax out to see the markings on the jacket. If it says RG-59, RG-59/U, or something similar, it will support composite video. If it says RG-6, RG-6/U, etc., you probably don't want to use it for that application.

The reason gets a bit technical, but basically, RG-59 has a solid copper center conductor, with a pure copper ground braid; while RG-6 is made with a copper-clad steel wire, with an aluminum foil & braid shield. Because RF frequencies travel more along the "skin" of both the center conductor and ground braid, it doesn't mind that below the copper clad of RG-6 is a rather poorly conducting steel wire. Composite (or baseband) video is much lower in frequency and travels more through the core of the wire and DOES mind having to plow through steel. For short runs, it probably wouldn't matter, but if you are taking it any distance the loss will eat up much your composite signal before it reaches the other end.

Just a head's up before you put too much time and effort into it.

[craiggsmith]

Thanks for all the info. Once upon I time I knew all the technical details behind this stuff, but it's been a long time and I've forgotten most of it. Usually my curiosity drives me to research things, but I haven't gotten around to it, so this was a good impetus to do so.

I didn't know that any wire would be made from steel; I would have assumed aluminum if not copper. I also didn't know how bad of a conductor steel was. I haven't had a chance to get over to the church to check the wiring. I trust that what you're saying is the norm, although my research tells me that the RG numbers don't really mean anything except essentially size and impedance, and that any cable could have any type of conductor and shield. I'm curious what our existing cables are for the composite jacks.

How long can you run standard composite video cable? I assume some are better than others. I hate dealing with stiff coax.

Back to the earlier comment of just needing to run a signal to the cultural hall -- this is usually the situation. I would prefer not to degrade the signal, but if I remember it didn't seem like there were any easy options; I think I would have to balance an analog signal. I guess HDMI can be run longer with good quality cable, but there doesn't seem to be any official specs over 45 ft. At any rate I don't like running cable across traffic areas when possible either, but getting our building retrofitted is not likely to happen for a long time.

But in a couple weeks for some reason our stake is hosting the Church and Scouting conference, which will require presentations to be sent via webcast to another building, so I figured I'd pursue the composite signal option first. Not sure why we are doing this; it seems they could find a better place to hold it. If any of you are attending you're welcome to help!

But we do have some funds to buy something now, so any suggestions would be welcome.

[russellhltn]

To add to the fun, composite is not designed to be sent long distances. The amplitude of the signal is fixed by spec. Some devices deal with a weak signal better than others. Some have noticed problems trying to feed video mixers with less than optimum signals.

[craiggsmith]

I have a cheap video distribution amplifier I got at radio shack -- but it's so lightweight I question what it actually does. If the amplitude is fixed I guess it just allows you to split the signal without as much degradation as opposed to amplifying a single signal. It would be interesting to measure it.

[russellhltn]

I have a cheap video distribution amplifier I got at radio shack -- but it's so lightweight I question what it actually does. If the amplitude is fixed I guess it just allows you to split the signal without as much degradation as opposed to amplifying a single signal.

Quite likely a unity gain amplifier with multiple outputs. It's job is distributing the signal rather than boosting it.

It would be interesting to measure it.

More than you probably wanted to know: Measuring composite-video signal

Note that video signals use the "IRE" unit instead of DC voltages to describe levels and amplitudes. Based on a standard 1 Vpp NTSC composite-video signal that swings from -286 mV (sync tip) to +714 mV (peak video)...

You'd need a scope of some kind. The fact that it's a non-sinusoidal signal and frequency of several MHz I think rules out DVMs for making the measurement.

It certainly seems possible to measure the sync pulse and adjust the signal so it's the correct amplitude. But I'm not sure just where you'd find such equipment.

[craiggsmith]

Used to have a scope ...

So I checked out the cables at our stake center - of my cable stash, all are RG-6 except one, the RG-59 cable I used to use before they installed composite video. I did like the flexibility of that one a lot more. However, that RG-59 is a copper-clad conductor, not solid copper. Of the RG-6 cables, some are solid copper and some copper-glad. I did confirm that the RF output on the rostrum is a direct feed from the cabinet, and although it's RG-6 it's solid copper as well; it's the same as the composite cables.

[Mikerowaved]

If your RG-59 is CCA (Copper-Clad Aluminum), it should work OK. CCA is only slightly more lossy than pure copper. The way to tell if your center conductor (or braid for that matter) is CCA rather than CCS (Copper-Clad Steel) is hold a magnet to it. If it has attraction, it's CCS. Yes, I've seen solid copper for RG-6, but it's not very common.

Sounds like you've got a few options to explore!

[craiggsmith]

I'll try that, thanks. One of the conductors bent very easily so I'm thinking aluminum; others are very stiff so might be steel.

Is it OK to run a regular RCA cable from the camera or projector in the middle to the jack on the side (~30 ft?), or should I run coax for that distance?