For the local theatre group's pantomime in the new year I want to provide a live vision feed of the stage to the dressing room area for cueing etc. I've got an old miniDV camera that can output live signal to s-video and thence to the AV socket on a TV; I've discovered that if I leave the tape door open it doesn't turn off - so far, so good. However, s-video leads are nowhere near long enough to bridge the distance - is there a physical limit on length or any alternative way to deliver video from camera to tv/monitor over a longer distance? I think I can also use RCA yellow/red/white sockets on camera - can they work over longer distance?
Derek
I have done this sort of thing years back when still teaching. I found that the Av leads worked best for me. However we did sometimes use low power AV sender and receiver in the backstage area, to power the tv set.
That worked - but a bit of picture disturbance. Also when using the AV leads over a longer distance we inserted a vcr along the way to boost the signal. Went in the AV in connection and then out via the AV out sockets.
No system was really perfect but we did provide some sort of picture back stage.
Gordon
We did something similar when I was involved in recording a dance show at a school. In our case we were relaying a main output from the vision mixing desk to a large screen TV located in the foyer.
We found that cheap s-video leads were a dead loss, because the luminance part of the signal was attenuated to the point that it almost disappeared. At the same time the chrominance came through strongly, resulting in a picture of such low definition that it was difficult figure out what we were looking at. There was just a sea of ill-defined colours on the screen.
To be fair, we did not try any expensive s-video leads, because in our case the problem cropped up less that an hour before the event was to start, which was when someone hit on the idea of putting the screen in the foyer for the benefit of the guests arriving.
Luckily we found a drum of low loss TV aerial cable to which we rapidly soldered phono plugs, and this did a superb job of relaying the signal, apparently without loss, to the target screen. Needless to say, we used the composite output from the desk.
UHF TV aerial cable has a good frequency response up to the gigahertz range. As a baseband PAL TV signal only needs a good response up to 6 MHz without significant loss or phase change, TV aerial cable can carry the video signal for many tens of metres to a remote display without the need for using VCRs or anything else as a booster.
TV aerial cable is 75 ohms, which is the correct impedance for transmitting a camera or any other picture signal from A to B. It has the additional benefits of being cheap and readily available on 100m drums from DIY warehouses and electrical wholesalers. The only real down-side is that it is a bit large and clumsy for soldering to phono plugs.
Above all, don't be tempted to use the cheap fly-leads which are only really suitable for transferring an aerial signal from a socket on the wall to the aerial socket on the back of the TV set. The quality is just not good enough.
Of course, the above will only transfer a picture signal. If you also need to transfer an audio signal for performers to get their cues, a long cable transferring a line level signal from the source to an amplifier in the changing room could easily pick up hum on the way. The way round this problem is to locate the amplifier adjacent to the source, and to use cheap speaker cable to send the signal to small speakers in the changing room.
I hope the above proves to be helpful to you.
Thank you, both - Martechnology and Gordon. Plenty for me to think about and, luckily for me, plenty of time to try some things out.
I was quite surprised that you can send video signals over long distances so easily so I'll conduct some tests, starting with the simple and progressing to the......use of a soldering iron!
Many thanks
Derek
When running long cables with video in public buildings, beware of deaf aid loops. These can modulate the video signal with audio, so that the picture shimmers and shakes when there is speech or music.
Leave enough time to test the system prior to the show.
RayL makes a very valid point about deaf aid loops. Having only encountered the need for a long video feed in a school where there was no such loop, I completely missed this possibility in my earlier waffle.
One way round this problem is a balanced feed using Cat-5 UTP cable which incorporates 4 twisted pairs. This would give the opportunity to transmit both composite video and sound utilising 3 of the pairs, or s-video and sound utilising all 4 pairs.
There should strictly be matching transformers to convert from the 75 ohm unbalanced source (the camera or the mixing desk) to the 100 ohm balanced UTP cable, and a similar transformer to convert back to 75 ohms unbalanced at the monitor end. I say strictly, because it may be possible to use only the Cat-5 UTP cable without transformers for "short" distances, perhaps up to 50 metres or possibly a bit more. I say 50 metres, because this is the wavelength of a 6 MHz signal, which is the highest frequency to be encountered in a PAL signal. Although the cable (100 ohms) would not be matched to the 75 ohm source and target, the reflections (and therefore ghosting) are not likely to be dire when most of the frequencies in the signal will have wavelengths considerably greater than 50 metres.
If you want to do a belt and braces job, there is a firm in Ealing, West London, called Vortex Communications which manufactures suitable matching units. I have no connection with this company, neither have I had any experience of using their products, but from looking at their product descriptions it appears that they do a good job. It would be worth a look at their PBE-303SR - Passive Balun for Composite Video and Stereo Audio:
http://www.vtx.co.uk/product.aspx?id=20
or their PBE-902 - S-Video + Stereo Audio Balun:
http://www.vtx.co.uk/product.aspx?id=26
These units must incorporate baluns for the video signal, but I don't know about the audio side. However, they specify 600 ohms for the audio input impedance, so I would guess that there has to be transformers involved.
Another possibility is to use baluns from an eBay supplier, These are aimed at the CCTV security market, but work perfectly well with any other video signal. These will convert the video signal to match the line, and you could just take a chance with the sound and hard-wire it straight through.
If you search for "balun cctv" on eBay, you should find plenty to choose from, but be aware that many advertisers are in China or Hong Kong, so delivery time could be an issue. However, it is possible to specify UK only.
Good luck!
Thank you, one and all. I think the best course of action is try and test some of the options at the actual location. I'm not sure when I'll be able to do this but I'll report back when I have some results.
Derek
I do a lot of live mix relays and use a composite feed mostly, at distances of around 500M.
Unless you buy a decent BNC crimping tool at around £50 it's easier to buy pre made BNCs from CPC.
use the longest practical length leads as every connection is a weak link but sometimes several lengths can be easier to handle.
If it is your building you can semi install them but bear in mind that if installing in a theatre space you need LFH cable and cannot punch through fire seals without making good.
Hearing loops do cause a beat pattern, especially on applause , mainly due to earth loops and using one of these normally takes the problem out.
I have several and they are a life saver.
If you use a Balun and CAT5 then loops generally don't happen.
One advantage of CAT 5 baluns is that ( if you buy the correct ones) they also handle audio which can be used for show relay, or as a paging system. ( or both as it is two channel)
I have a set that I bought, unused, from ebay for £50
DO Not use flat screen TVs if you can avoid it, unless latency is not an issue.
Old CRT monitors are dirt cheap and have no latency, which can throw a conductor or musician. proper ones also have an in and out plus termination switch.
Most cameras are sensitive to IR which means that many can see in the dark if the tungsten lighting still glows IR even if the audience cannot see,
My current job is in a multi space theatre with TV studio and we wired all the video connections to be HD-sdI as it worked out cheaper, and all the theatre video links arrive via a patch in the theatre control rooms and can then be sent to the TV gallery which acts as a hub to send them on to any other control room, then back to a theatre.
We installed loads of CAT 5 as well.
HdD-SDI is OTT for your needs now but investigate the cost as it worked out cheaper than SD in my case. HD-SDI also handles 16 audio channels, given the correct boxes.
all our control rooms have cheap B&W security cameras showing the performance space and it is easy to send the image to the SM's desk as well as backstage.
CPC is a good source of amps, cat 5 converters and other useful items at cheap prices.
If you use the balun and cat-5 approach, common-mode will not be a problem because the line will have baluns at each end, and common-mode interfering signals cannot pass through transformers. This assumes that both the video and audio signals are coupled to the UTP cable via appropriate baluns.
However, if you use cheap CCTV market baluns for the video part of the signal but hard-wire the audio end to end, there may be a common-mode issue with the audio side. I have found that a 600 / 600 ohm broadband transformer such as the Sowter 4603 ( http://www.sowter.co.uk ) at the receiving end of the line, one for each channel, will prevent common mode signals getting through and disrupting the audio signal. We used this approach successfully for recording, so it should work equally well for a feed to the changing room. If your audio feed to the changing room is not critical in respect of frequency response, cheaper transformers (such as telephone 300 Hz to 3 kHz transformers) should work and be rather cheaper than the Sowter items - no disrespect to the Sowter transformers because they are excellent.