Bazz339 Posted May 2, 2015 Share Posted May 2, 2015 For a 1 off church function (Although it is a need which recurs every once in a while) I need to relay composite video and audio from a church to the church hall. Total cable about 80-100m depending on location of equipment. 1 day event. I have simply used a BNC cable before with separate audio but the church has an induction loop which interfered with the signal, this time I intend to cross the induction 2m above it, I think I ran parallel and adjacent for 10m down the church before. I am contemplating using simple 3 x Phono (Audio L & R + Video) Baluns boxes at either end of a SHIELDED Cat5 cable. Anyone used this arrangement over this sort of distance?Given the lay up of the cable I am hoping this will deal with the interference from the induction loop. Anyone used this before. I don't want to buy the materials to try it if it isn't likely to work. I have the baluns boxes and the necessary to terminate Cat5. Audio (Line level) I can either send down the Cat 5 (I have line level balance/isolating tranformers) or through XLR. Might I be better hiring something? Budget is limited. Link to comment Share on other sites More sharing options...
Dave m Posted May 2, 2015 Share Posted May 2, 2015 Is the audio modulating the picture caused by the loop?Using a hum eliminator on the feeds may help, so that the earths are isolated I don't know if the baluns will effectively do this already. Link to comment Share on other sites More sharing options...
djw1981 Posted May 2, 2015 Share Posted May 2, 2015 I did something similar for video relay to church creche. We took the audio as a split of the main PA feed and ran it balanced down mic cable, and composite video over Cat5, with passive baluns, past some meaty 125A 3phase (main supply to vodafone transmitter) without incident. Link to comment Share on other sites More sharing options...
timsabre Posted May 2, 2015 Share Posted May 2, 2015 It's all about ground isolation... Which baluns would give you. A bnc cable would give a ground loop to the projector mains connection which would cause the induction loop noise described. Link to comment Share on other sites More sharing options...
Bazz339 Posted May 2, 2015 Author Share Posted May 2, 2015 I am more concerned about induction from the loop causing interference. Take the point about earth loops. Not sure whether the boxes I have give any isolation for video. Not bothered about audio as I have line balancing/isolating boxes. Link to comment Share on other sites More sharing options...
timsabre Posted May 2, 2015 Share Posted May 2, 2015 In my painful experiences with induction loops, the interference only happens when you have an earth loop. If you can isolate the earths then you don't get interference by induction. Link to comment Share on other sites More sharing options...
adamharman Posted May 2, 2015 Share Posted May 2, 2015 In my painful experiences with induction loops, the interference only happens when you have an earth loop. If you can isolate the earths then you don't get interference by induction.Yes, or any unbalanced signal which by definition has to be earthed. Guitar pickups are a favourite for it when you forget to turn the loop off.... Link to comment Share on other sites More sharing options...
richardash1981 Posted May 3, 2015 Share Posted May 3, 2015 I thought that the video over CAT5 devices I have seen have been transformer based, so could give isolation. However the CPC Pulse one I got cheap and have never used (but just taken apart) don't seem to be like this - they have end-to-end DC continuity in the video channel! Oddly there is a device on the PCB marked 'T1' in the video channel, but it has DC continuity input to output in both leads, but no DC continuity between signal and ground. I'm beginning to wonder if these extenders actually work, or if the transformers are inserted on the PCB wrong ... The problem with transformer baluns comes when someone has been clever and wires the incoming / outgoing ground to the 4th pair at both ends 'to provide ground continuity', thus wiping out the isolation. This depends on the designer of the specific isolators. The good news is that if the ones you get are grounded, it shouldn't be hard to defeat if you can get them apart to figure out which pair in the cable is used for what - you probably just need a CAT5 lead with one of the four pairs disconnected to break the end-to-end grounding. Overall, I suspect that a video 'hum eliminator' in the composite lead may be the reliable solution - and if you buy cheap AV-over-CAT5 adaptors, test them when you get them! Link to comment Share on other sites More sharing options...
Bazz339 Posted May 5, 2015 Author Share Posted May 5, 2015 This is the schematic for the baluns boxes I have. http://i1205.photobucket.com/albums/bb425/17234/20150505_142208_zpsyxiujelg.jpg There is a DC path between the screens on Video and Audio R. Not apparently on Audio L. Can someone give me a link to a reasonable hum bucker please? Link to comment Share on other sites More sharing options...
timsabre Posted May 5, 2015 Share Posted May 5, 2015 errr... I think someone has drawn the balancing transformers the wrong way round on that diagram... they'd just short out the signal if they were wired like that Link to comment Share on other sites More sharing options...
DrV Posted May 5, 2015 Share Posted May 5, 2015 errr... I think someone has drawn the balancing transformers the wrong way round on that diagram... they'd just short out the signal if they were wired like thatI bought something very similar from CPC once and they were actually built like that. Fortunately the transformer pins were on a square layout so I just desoldered them and put them in how I wantedthem! Dave Link to comment Share on other sites More sharing options...
timsabre Posted May 5, 2015 Share Posted May 5, 2015 I bought something very similar from CPC once and they were actually built like that. Fortunately the transformer pins were on a square layout so I just desoldered them and put them in how I wantedthem! Interesting, RichardAsh 2 posts above says the same thing. I can't imagine why they would be built like that, or even if they would work - the transformer would just short out all the signal above a certain frequency. Link to comment Share on other sites More sharing options...
sandall Posted May 5, 2015 Share Posted May 5, 2015 errr... I think someone has drawn the balancing transformers the wrong way round on that diagram... they'd just short out the signal if they were wired like thatAre they maybe RF filters, as drawn, rather than transformers?I wouldn't expect video to be transformer coupled! Link to comment Share on other sites More sharing options...
timsabre Posted May 5, 2015 Share Posted May 5, 2015 Could be, but it's not a balun then... Link to comment Share on other sites More sharing options...
Solstace Posted May 5, 2015 Share Posted May 5, 2015 Hmm... this perhaps explains why my CPC audio baluns, bought as a pair, and shown on the casing as being wired the same way, never did seem to work except on the left channel, if I recall correctly. Never did get time to either send them back or get the lids off... Link to comment Share on other sites More sharing options...
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