Running Video Cable next to induction loop cable

[Bazz339]

A local church wants to permanently mount a projector. My suggestion is one mounted on the side wall. I suspect this may be part of a continuing process of change including changing the sound system from the simple one they have with a mixer amp to something that can be "Operated" probably at the back of the church.

 

The best option may ultimately be to install the cabling up and across the ceiling but I think that there may some ongoing discussion to be had before a final location for control is determined. I am inclined to suggest an easier temporary solution of dropping the cables down, and along following the route of the induction loop. My experience is that close proximity to an induction loop causes interference with VGA cable but I have no idea what quality the cable was (Not my installation) , so I am interested in other people's experiences.

 

Does it cause interference with decent fully screened VGA cable?

 

On an installation I did, I used a powered Aten VGA to CAT 5 converter at both ends with screened cable between, that worked OK but I think I was able to maintain some separation on that installation

I would not be able to on this one.

 

Is the induction loop likely to interfere with an HDMI signal if the cable is run adjacent to it?

 

The projector will probably have wifi built in.

 

Any other suggestions for minimising induction loop interference?

 

Regards

 

Bazz

[Dave m]

I have found that on composite feeds, the loop causes a patter that matches the sound.

You can stop this with a hum eliminator as I think it is earth related.

 

CAT 5 may be proof against this by use of baluns

HDMI over Cat 5 tends to be limited to shorter cable runs

[revbobuk]

Current church installation I'm doing uses HDBaseT direct to a compatible projector, and as this is fully digital, no issues with loop breakthrough. Yes, I've found that even decent VGA cables suffer from this - it's a kind of 'shimmer' that is clearly the audio breaking through. Some colours are more susceptible than others, oddly.

[handyandi]

Yes loop interference on VGA cable is very noticable if they are run parallel. Again like the others reverted to Cat5 baluns, but not the cheep CPC passive ones as they also suffered from interference. Ended up with Kramer actives & I also have a Databay one with audio & they are fine.

[Yorkie]

At church our main projector is about 3' from the loop cable, the output from the TVone Task cat5-vga runs into a 50cm vga lead and we get interference from the loop. We can cope with it for now, mainly because we have never had anything fed to the loop during the songs-the time people are concentrating on the screen most intently. We're having a full refit in a couple of years so will switch to a HD digital signal then

[timsabre]

As Dave M says it is earth related.

If you use baluns to send the VGA signal (or put in a VGA hum eliminator), that gets rid of the interference as there is no ground path any more.

 

Going digital is not necessarily a solution as the interference can make the projector unable to read the digital signal and go blue or black screen.

[Stuart91]

If you are experiencing problems, it might also be worth taking a look at the output level on the loop driver. I've been called out to a couple of churches that have had similar problems, only to find that their loop amps have been running at ridiculously high levels. I suspect this may have been due to people trying to "helpfully" make adjustments when hearing aid users have had difficulty.

 

Returning the output to a more sensible level can sometimes make the problem unnoticeable, but won't make it go away completely.

[Bazz339]

Thank you for the replies, sorry I have not checked the thread for a few days.

 

I have found that on composite feeds, the loop causes a patter that matches the sound.

You can stop this with a hum eliminator as I think it is earth related.

 

CAT 5 may be proof against this by use of baluns

HDMI over Cat 5 tends to be limited to shorter cable runs

 

I had assumed it was the audio signal being induced in single core screened video cable (X how there many are in the VGA Cable).

 

 

Current church installation I'm doing uses HDBaseT direct to a compatible projector, and as this is fully digital, no issues with loop breakthrough. Yes, I've found that even decent VGA cables suffer from this - it's a kind of 'shimmer' that is clearly the audio breaking through. Some colours are more susceptible than others, oddly.

 

HDBaseT is new one on me. I would suggest that some colours being more susceptible than others may be related to the orientation of the video cable with regard to the induction loop cable. I suspect the cores may run in a relatively straight line within the outer sheath. Turning the cable along its length through say 45 or 90 degrees may affect which colours as some would be slightly neared the loop cable and others more screened from it.

 

 

Yes loop interference on VGA cable is very noticable if they are run parallel. Again like the others reverted to Cat5 baluns, but not the cheep CPC passive ones as they also suffered from interference. Ended up with Kramer actives & I also have a Databay one with audio & they are fine.

 

I have used Aten VE022 send and receive which are active. It worked in the permanent installed I used it on but the Cat5 cable was several feet from the induction loop cable.

 

As Dave M says it is earth related.

If you use baluns to send the VGA signal (or put in a VGA hum eliminator), that gets rid of the interference as there is no ground path any more.

 

Going digital is not necessarily a solution as the interference can make the projector unable to read the digital signal and go blue or black screen.

 

Fair comment.

 

If you are experiencing problems, it might also be worth taking a look at the output level on the loop driver. I've been called out to a couple of churches that have had similar problems, only to find that their loop amps have been running at ridiculously high levels. I suspect this may have been due to people trying to "helpfully" make adjustments when hearing aid users have had difficulty.

 

Returning the output to a more sensible level can sometimes make the problem unnoticeable, but won't make it go away completely.

 

Loop output is fine as far as I know. I put it in and it is one of the smaller amps I have used and is driving three turns but it does cover well.

[Bazz339]

I installed the projector using the Aten VE022 send and receive boxes and some screened Cat 5 cable. There was a high frequency tone on the sound system when the source computer was plugged into it and the projector, eliminated using a Interspace Industries audio isolating box. There was still some some slight interference on the projected image caused by the induction loop, but acceptable for the time being. Might look at earth loops on the video side as although the audio was transformer isolated there was presumably still the opportunity for a loop through the laptop psu, should have tried unplugging it shouldn't I? will try that at some point.

[sandall]

Loop output is fine as far as I know. I put it in and it is one of the smaller amps I have used and is driving three turns but it does cover well.

I'm not sure whether it affects your problem, but why 3 turns? AFAIK all the major loop amp makers recommend a SINGLE turn loop of <1 ohm impedance. The only time I've met 3 turns was in a local church I was refitting, where the previous system had a length of 3-core mains, with the cores connected in series to give a 6 ohm load, driven from the speaker terminals of a MOSFET "hi-fi" amp - no eq, no compression - ugh!!

[alistermorton]

As I think I've mentioned before, many years ago I saw a design for an induction loop which which recommended doing just that - creating a 3 turn coil. This was in the 70's - maybe ways of thinking and designs have changed over the years.

[MarkPAman]

I remember making 3 turn loops out of flex in the early 80s for use with "proper" loop amps. Can't say I really remember why, but I assume it's what the instruction book said - I'm usually pretty good at reading the manual rather than making things up...... :unsure:

[timsabre]

As I understand it multiple turns were used to increase the loop impedance as older amps could not drive <1 ohm - the "on" impedance of the output stage transistor would end up bigger than the loop impedance. With the coming of better mosfets with low "on" impedance, single turn loops with higher current became possible and this gives better field strength.

[Bazz339]

The loop amplifier replaced one that was there before, and yes, it was as some have suggested a simple mixer amplifier w using the low z speaker out with multi loop turns to get the impedance up. Thinking about it, I may have reconfigured the wiring to parallel or I may have used 2 turns in series to boost the gain when I installed an induction loop amp and used the existing mixer amp to power a pair of loudspeakers. Unfortuantely the loop cable is somewhat masked by a cast iron pipe in front of it but a) I did not install it b) I was getting an appropriate level and tonal quality off the loop.

 

However, at the moment I have the loop on the outside of the pipe and the Cat cable feeding the projector on the congregation side. I may swap them over as it is not too big a job as that would put the Cat cable outside of the loop (just) and mean that the loop is no longer screened directly by the pipe. Lets not get hung up on the loop, it works well for speech.