Question for Comtek IFB users

[Stephen Hall]

I've got a question for those of you using Comtek IFBs for on-set monitoring.

A while back I bought a fairly old Comtek system: 1 transmitter and 2 receivers. It works reasonably well, but I find that if the person wearing the receiver is within a couple of feet of a fluorescent fixture ( like a Kino Flo light , flatscreen monitor or laptop screen), there's a lot of noise and hash and the thing is unusable.

Needless to say, on a contemporary set, this is pretty limiting.

If you have newer Comteks, do you have this problem ? For what it's worth, I'm told they're on the order of 20 years old. There is an "H" indicator on the front of the receivers ( frequency, I think ).

Thanks in advance,

Stephen H

[Claire Buckley]

Hi Stephen,

You might be advised to contact Comtek.

I suspect from your description you are getting switching power spikes (thyristor PSU switching) into the comms. This will be at mains frequency and its harmonics and sounds anything from "buzzing" at the LF end to "shash" at the HF end.

Eiither you have an (unlikely) AM carrier comms system (as the FM carrier and demod should provide sufficient AM rejection to limit this) or the FM demodulator in the receiver has drifted away from the optimum S curve point (which gives max AM noise rejection) - but unlikely if it's happening on both receivers - then that puts the source of the problem into the TX unit. Or the TX unit is out of mod/demod aligment with the receivers.

Could be an antenae or (relative) grounding issue. Have a word with Comtek - could be you need some maint on the system.

1. Does the problem only become audible upon transmitting from the TX unit?
2. Do you get the problem regardless of whether the unit is TXing or not - is it a receiver side issue?
3. Have you tried swiching off offending units one at a time to gauge the problem?

:)

[Stephen Hall]

Thanks for your response, Claire.

I should have been more clear when I stated the problem. This happens when someone wearing a receiver (either of the two receivers ) is within 18" to 24" of a fluorescent lamp of some kind: laptop screen, flatscreen monitor, or Kino light fixture -- the audio they receive on the Comtek is swamped by static/buzz.

Since these fluoro lamps are all over sets, these days, it makes my IFBs less and less useful. I haven't tested moving the transmitter close to the lights, but it seems to be the receivers that are affected.

I'm just curious whether more modern Comteks are affected in the same way. If not, I assume it's because mine were built in the days of coal-fire fresnels and gaffers rubbing two sticks together very, very quickly to light a set. :-)

Thanks again,

Stephen H

[Greg Miller]

Steven:

I guess I have a "global" sort of question. Do you care whether your present units are working as well as possible, or whether they can be fixed? Or do you ONLY care whether newer units work better?

If the former, then it might be truly helpful if you'd answer Claire's questions, especially the first two, and, as Claire suggested, to contact the factory.

OTOH, if you're ready to give up and scrap your present units (assuming brand new ones are better), rather than investigating adjustment/repair of them, then I guess you don't need to provide any more specific info about your problems.

Just my 2¢ worth for the sake of clarification.

[Stephen Hall]

Ok, Greg makes a good point when he asks what I'm looking for.

At this stage, I really just wanted to hear something like either: "Oh, IFBs all do that" or "No, my IFBs don't suffer from fluorescent lamp problems like you describe."

I haven't done a full-on troubleshooting session with them, yet, so can't do Claire's triage.

Anyway, thanks for your responses, everyone.

Stephen H