Hi All,
I am having a minor issue with a wireless mic set-up. I believe the wireless mic is a Shure SM-318 using the 114/116MHz frequencies (I think). Anyway, I have tested it on 5 or more systems and it works perfect. I am attempting to use it with a society I am involved with.
I turn up early to the meetings, connect the wireless receiver into the wall (there is already an amp and speakers in the room we use). Test it and it works fine. When the meeting starts properly there are 50 or more people present. The microphone then just doesn't seem to work correctly, sound either fails all together or comes and goes, or seems crackly.
Again after the meeting has finished and most have left, I test it again and again it works fine. Initially we thought it was the equipment but after testing it before and after meetings and on other systems, I am struggling to find the cause and/or a solution. After tonight I am assuming it is not the equipment as such.
I am assuming something is causing interference. Could it be hearing aids? I only ask as we only get a problem when we have an audience present. Hence I am assuming it is linked to something in the audience.
Any thoughts or suggestions are welcomed.
Nick
I am having a minor issue with a wireless mic set-up. I believe the wireless mic is a Shure SM-318 using the 114/116MHz frequencies (I think). Anyway, I have tested it on 5 or more systems and it works perfect. I am attempting to use it with a society I am involved with.
I turn up early to the meetings, connect the wireless receiver into the wall (there is already an amp and speakers in the room we use). Test it and it works fine. When the meeting starts properly there are 50 or more people present. The microphone then just doesn't seem to work correctly, sound either fails all together or comes and goes, or seems crackly.
Again after the meeting has finished and most have left, I test it again and again it works fine. Initially we thought it was the equipment but after testing it before and after meetings and on other systems, I am struggling to find the cause and/or a solution. After tonight I am assuming it is not the equipment as such.
I am assuming something is causing interference. Could it be hearing aids? I only ask as we only get a problem when we have an audience present. Hence I am assuming it is linked to something in the audience.
Any thoughts or suggestions are welcomed.
Nick
Hi All,
Think I may have just answered the question. When writting the post above it occurred to me that the mic is VHF. Doing a quick google for hearing aids it shows some also using VHF. I don't know the exact frequencies but am assuming that this is the problem of the mic and hearing aid interfering.
I therefore assume that a UHF system wouldn't have the same problem. Can anyone confirm this? If so, can anyone suggest an inexpensive wireless (tie clip) system?
Cheers,
Nick
Think I may have just answered the question. When writting the post above it occurred to me that the mic is VHF. Doing a quick google for hearing aids it shows some also using VHF. I don't know the exact frequencies but am assuming that this is the problem of the mic and hearing aid interfering.
I therefore assume that a UHF system wouldn't have the same problem. Can anyone confirm this? If so, can anyone suggest an inexpensive wireless (tie clip) system?
Cheers,
Nick
Hi,
It's possible hearing aid devices are causing interference, but lots of things can cause problems in the VHF band. Are there any RF based hearing impaired transmitters in the room?
UHF is much less likely to be affected if it is from VHF hearing impaired systems, but UHF is becoming tricky with all the bandwidth reallocation that's been going on the past few years.
There are many cheap UHF systems, but you get what you pay for with wireless. At minimum, I would suggest a system with a true diversity receiver and research what DTV stations are operating in your city.
It's possible hearing aid devices are causing interference, but lots of things can cause problems in the VHF band. Are there any RF based hearing impaired transmitters in the room?
UHF is much less likely to be affected if it is from VHF hearing impaired systems, but UHF is becoming tricky with all the bandwidth reallocation that's been going on the past few years.
There are many cheap UHF systems, but you get what you pay for with wireless. At minimum, I would suggest a system with a true diversity receiver and research what DTV stations are operating in your city.
Work with a pro dealer. You should be able to try a system on approval. They don;t want to sell you something you won't be happy with. It does sound like interference. getting a system in a different RF band would seem expedient.
Hi,
Thanks for the replies. I know there are various things that could cause interference but thought it may be hearing aid related as the problem only occurs when people start to turn up. So thought it could be something related.
I am unaware of a hearing loop or similar around the room, but am now investigating that possibility.
As for DTV and reallocation, I had thought about that with UHF. Anyway, will investigat the above first, as getting what you pay for, I do agree but being a small non-profit group, we simply cannot afford much, hence having gone for a VHF system.
Anyway, thanks for the ideas guy, very much appreciated.
Nick
Thanks for the replies. I know there are various things that could cause interference but thought it may be hearing aid related as the problem only occurs when people start to turn up. So thought it could be something related.
I am unaware of a hearing loop or similar around the room, but am now investigating that possibility.
As for DTV and reallocation, I had thought about that with UHF. Anyway, will investigat the above first, as getting what you pay for, I do agree but being a small non-profit group, we simply cannot afford much, hence having gone for a VHF system.
Anyway, thanks for the ideas guy, very much appreciated.
Nick
The US FCC department recently (when all TV stations went digital) changed the frequency bands that wireless mics are permitted to use. So other new devices may be now operating in a mic's older frequency band.
Hi,
I am in the UK and although the same hasn't happened here yet, I dare say it will.
Even if that was the case, it wouldn't explain this situation. That is everything works fine until our audience turn up. The chances of our audience having any technology, other than a hearing aid or mobile phone, that could cause interference is slim.
That is what makes me think the problem is related to the hearing aids, or perhaps an induction loop system for the hearing aids.
Anyway, thanks for the info, something to watch out for in the future.
Nick
I am in the UK and although the same hasn't happened here yet, I dare say it will.
Even if that was the case, it wouldn't explain this situation. That is everything works fine until our audience turn up. The chances of our audience having any technology, other than a hearing aid or mobile phone, that could cause interference is slim.
That is what makes me think the problem is related to the hearing aids, or perhaps an induction loop system for the hearing aids.
Anyway, thanks for the info, something to watch out for in the future.
Nick
If you are interested in other strange problems, the EMC (EMI/RFI) group in the UK publish a journal with a regular column "Banana Skins" that documents other unusual problems.
You may have to do a simple sign-up.
EMC Information Centre - The EMC Journal (Free in the UK)
You may have to do a simple sign-up.
EMC Information Centre - The EMC Journal (Free in the UK)
Hearing aids are not likely to be the cause. No radiated RF to speak of, and because they are made to go in the ear, they are subject to very tight regulation. What speedskater said about the change in the spectrum alocation could be a clue. Try a longer wire between the receiver and the amp so that you can move the receiver around when the problem occours. You might find a sweet spot that cures the problem.
Hi,
I didn't mean to imply the hearing aids themselves but perhaps something linked to them such as a hearing loop? Should have been a bit clearer. Have already tried different cables and placements.
Moving the receiver around has had no affect. This is why I think it has to be something related to the audience and the only thing I could think of, apart from mobile phones was hearing aids/loops. I have ruled phones out by a few simple tests.
Thanks for the suggestions though, at least I know I have covered the most of the possible causes.
Nick
people (=ugly bags filled with water) provide serious RF damping.
Is there a direct line of sight between microphone and receiver?
regards
Hi Juergen,
Thanks for the reply. Yep, there is a direct line of sight, typically the speaker is within 5 ft of the receiever but can be up to 15ft away, but always in a direct line of sight.
So not sure what it is that is going on...
Thanks for the suggestion.
Nick
Well if it is some sort of assisted hearing transmitter, it is not likely the hearing aids in the seats bothering you. If such a system exists in the venue, find out who is in charge of it. During sound check, have the system enabled and disabled and see if the presence of it disturbs your operation.
If the squelch is accessible, try turning it down a little.
If the squelch is accessible, try turning it down a little.
Hi,
I'm also in the UK and the first thing I can tell you is that the frequencies you mention have never been legal here...
Currently, there are a few channels between 175 and 178 MHz ( VHF ) and 860 to 863 MHz ( UHF ) which are available license free and either shouild work without interference.
What seems likely is that your setup depends on room reflections of the signal and when the audience arrive they absorb a lot of the signal and you get problems.
I use both wavebands for headset mics with my 60's/70's band and even with good branded equipment I still find dead spots.
Diversity receivers are supposed to stop that happening, but unless the two aerials are a long way apart, they are no better than the simpler gear.
The best advice I can offer is to get professional help - including a site-survey if needed. Don't just buy from a brown-box shifter to save money.
I'm a radio ham, so I understand the technology better than most users, but I still get problems.
Good luck, Graham.
I'm also in the UK and the first thing I can tell you is that the frequencies you mention have never been legal here...
Currently, there are a few channels between 175 and 178 MHz ( VHF ) and 860 to 863 MHz ( UHF ) which are available license free and either shouild work without interference.
What seems likely is that your setup depends on room reflections of the signal and when the audience arrive they absorb a lot of the signal and you get problems.
I use both wavebands for headset mics with my 60's/70's band and even with good branded equipment I still find dead spots.
Diversity receivers are supposed to stop that happening, but unless the two aerials are a long way apart, they are no better than the simpler gear.
The best advice I can offer is to get professional help - including a site-survey if needed. Don't just buy from a brown-box shifter to save money.
I'm a radio ham, so I understand the technology better than most users, but I still get problems.
Good luck, Graham.
Yes, you are filling your room with VHF absorbers. For regular use your best bet is a semi-pro UHF system like Sennheiser G3. Even that can suffer problems on the license-free band - in our church we can only use three of the four legal channels because one always suffers interference. We have the earlier G2 system (G3 has six channels in each band).
In the US wireless mics do not operate in "license free bands". We have been operating illegally for a long time. The recent FCC changes are trying to bring that to an end via a national database so that wireless and "white space" devices can coexsist. In theory anyway.
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