Can cell phones interfere with wireless mic?

D

David W. Richardson

Chapelgrove Films
My church continues to have a problem with the wireless lapel mic our preacher wears and uses for a small portion of the service.

Quick background. The sound mixer and receiver for the wireless mic are located at the opposite end of the sanctuary from where the preacher is. We use a Shure T4a receiver and Shure T1w transmitter.

Whenever I test the mic during the week, from the same position the preacher is in when he uses it, it works fine. Range doesn't appear to be an issue -- I've worn the mic and gone completely out of the sanctuary and up to the back exit of the building itself, and still the signal worked. But all too often during the service, when the preacher reaches the part where he uses this mic, the signal is either gone or it pops in and out -- mostly out.

Last Sunday the first 3-4 seconds it was fine, then completely disappeared. While he was still using it, I raised the receiver up as high as I could hold it, I turned it every which way, changed the position of the antennae, and checked that the cables were tight. Even turned the volume knob on the receiver all the way up. Nothing helped.

We had this same problem before, but the previous two Sundays it worked flawlessly.

Someone wondered aloud if cell phone usage by members of the congregation could cause the problem. I have to admit, I don't know for sure. I believe our Shure system is older, though I'm not sure how old.

Do you folks have any experience with this? Is it possible that cell phone usage in the sanctuary could cause this signal dropout?

I'd appreciate any advice or suggestions.

Thanks!
 
The problem does sound like intermittent interference. You don't say what frequency band this unit is on. However, it is a very low-end system, which means that the receiver filtering is probably not great. What is likely happening is one of two things: A) all the cell phones in the room are radiating RF, and, although it is not in the same band (probably) as your unit, it is causing the receiver to "de-sensitize" thus causing dropouts. Or, B) that you are in a band that is used by another source, such as LTE (in the 700 MHz band) and when all those people are there with their LTE phones, it is directly interfering with your system. By the way, it is illegal to use a wireless microphone in the US in the 700 MHz band (since 2010).
 
Thanks Karl. I checked the frequency once before, and thought it was operating in the legal range. But I will double-check it today.

Since the wireless dropout problem only occurs when there is a congregation (and others) in the sanctuary, I'm inclined to believe that cell phones and other devices might very well be the problem. At one time I had thought that simply the mass of human bodies between transmitter and receiver might be the culprit. However, the wireless has worked fine on occasions when we had a pretty good crowd in attendance. One such day was the day I was ordained and installed as a deacon, not long ago.

Another possible issue is another wireless system we use -- it's a Nady system for the hearing impaired. The transmitter is always on during the services, but there may or may not be someone using one of the receivers in the congregation. I don't really know if the dropouts correlate to times when someone was using the receiver. I'll have to start a log of that. I do know that someone was using the receiver this past Sunday. But they would be using it for the entire service, so it seems if that were the interference then I wouldn't have gotten the 3-4 seconds of clean signal from the lapel mic at all.

I appreciate the help! Thanks so much!
 
Doing further research, it appears that the Shure T1 Body-Pack transmitter operates on a VHF frequency range of 169.445 MHz to 216.000 MHz. The T4a receiver operates in a VHF range of 169.445 MHz to 240.000 MHz. The T4a receiver can also operate UHF in the range of 596 to 865 MHz. But since the Body-Pack transmitter can apparently only do the VHF 169.445 to 216.000 range, I assume we're okay on that, from a legal standpoint.
 
Cell phones can cause interference. It was really bad in the early days of Nextel systems. It would sound like an outdoor sprinkler system going back and forth, but it was usually only when the phones were in very close proximity to the Tx or Rx.

Wireless can be very frustrating, sometimes. Last week we were shooting segments with three to four talent each time and all on the same block. Everything was fine until the last day and we were in a room we hadn't shot in yet. All of a sudden we started taking hits and drop-outs on one of the units. We stopped down and started trouble shooting as fast as we could. Our first instinct was something was stepping on one of them. We turned all the Tx's off and did a scan and to our surprise there was absolutely NOTHING showing up. There is always something floating around in block 22(Lectrosonics), but this time no a single blip. I was shocked. We fired back up and knocked out the segment and then figured out it was one of the antenna on one of the packs getting hit. It was a replacement antenna that is supposed to be "unbreakable", but they are VERY stiff and if you hit them just right the signal is affected.
 
The simplest solution would probably be to simply move the receiver up to the front. The closer you can get the receiver to the transmitter, the less potential problem you will have.

The question about frequency wasn't about legality. The question was how near (or far) the operating channel is from potential interference. Operating down around and below 200 MHz puts it about as far away from cell phones as you can get. Besides, cell phone interference would be much more intermittent. It would not manifest itself as simple fading or complete failure.

It sounds like the wireless mic is pretty old as those VHF systems aren't very popular in the 21st century.
 
That's very interesting, Run&Gun!

I'll admit I'm a novice when it comes to wireless systems, as you can probably tell. Our system is pretty static. Receiver is always in the same place. Transmitter is nearly always in close to the same place.

I have put on that wireless mic and walked all over that sancturary, talking into it. No dead spots that I could find. I've laid flat on the floor in front of the front row of pews, so that every pew there was between the mic antenna and the receiver antennae, and had no problems at all. I wore the mic and walked to the far end of the building, putting at least 3 walls between me and the receiver -- no problem.

So I have to believe something changes on Sunday mornings. The congregation is there. The choir is there, although they are behind the preacher so they're not between him and the receiver. Pianist and organist are there, but also not between the preacher and the receiver, and neither plays during the children's service. So it seems that the only obvious difference is either the warm bodies between transmitter and receiver, or their cell phones and whatever other tech, like tablets or handheld games, they might have with them.

If cell phones and other gadgets are the problem, then the solution is most likely new wireless gear, since I doubt everyone will turn their gadgets off. (Some are firefighters and paramedics who have to be reachable.) So any recommendations for updated gear for a church on a tight budget?
 
David W. Richardson said:
Doing further research, it appears that the Shure T1 Body-Pack transmitter operates on a VHF frequency range of 169.445 MHz to 216.000 MHz. The T4a receiver operates in a VHF range of 169.445 MHz to 240.000 MHz. The T4a receiver can also operate UHF in the range of 596 to 865 MHz. But since the Body-Pack transmitter can apparently only do the VHF 169.445 to 216.000 range, I assume we're okay on that, from a legal standpoint.
Click to expand...

In those frequencies cell phones should not have any impact on the noise floor, which is what may occur if you are operating in or 'near' the 700 MHz band which is now allocated to cell phone use in many areas.

In the olden days... and still in some cases the present... the GSM signaling method would cause sever noise in audio equipment... analog phones, audio playing equipment and of course during recording.

The 'noise' usually sounded like a clacking or chatter of short bursts of noise, very distinct.

If you say the audio 'drops out' that is not a symptom of GSM interference that I've heard of...

In the VHF 'high' TV band that you list, TV channels 7-13 operate, or 174 to 216 MHz. Don't know if there are any channels broadcasting in your area in that range... if you have an antenna based TV... run through channels 7-13...

There could be a mechanical cabling/connector issue that the preacher seems to elicit... and you don't... is the preacher active on stage/pulpit or just standing and delivering the sermon?

Contacts can also have issues if worn or the like.

This is the point that I'd get out my spectrum analyzer... and look at the frequency the device is operating on... but that's pretty expensive if you don't happen to have one around.

I did find this... http://www.ecrater.com/p/21650822/rf-spectrum-analyzer-using-dvb-t?gps=1&id=115931170339 ... for $17 it could be worthless junk... but it does use a TV tuner... and so would work in your bands of interest...
 
Richard Crowley said:
The simplest solution would probably be to simply move the receiver up to the front. The closer you can get the receiver to the transmitter, the less potential problem you will have.

The question about frequency wasn't about legality. The question was how near (or far) the operating channel is from potential interference. Operating down around and below 200 MHz puts it about as far away from cell phones as you can get. Besides, cell phone interference would be much more intermittent. It would not manifest itself as simple fading or complete failure.

It sounds like the wireless mic is pretty old as those VHF systems aren't very popular in the 21st century.
Click to expand...

I had thought that too, about if it was cell phone interference then it would be more consistent. But let me ask you this...does the cell phone cause more interference when it's in USE, as opposed to just sitting on but idle?

Here's my thinking. There is usually only one place during the service where the preacher leaves the pulpit, and that is the children's service. This is where he uses the wireless mic. He goes down and sits on the top step and talks to the children. Now my first thought had been that, being lower down, he was putting more parishoners' bodies between the transmitter and receiver. But as I've said, I raised the receiver very high up to clear the line-of-sight and it made no difference.

But what about this? This is the one part of the service where many of the older kids and adults feel disengaged from what's going on. This might be there very time they would check phone messages, send texts, check Facebook, etc. So that leads to my question -- would active use of the phones and other gadgets create more interference than the phones just passively sitting there?

I REALLY appreciate all the help and advice of you seasoned pros! You're the BEST!
 
David W. Richardson said:
I had thought that too, about if it was cell phone interference then it would be more consistent. But let me ask you this...does the cell phone cause more interference when it's in USE, as opposed to just sitting on but idle?
Click to expand...

Re: teens using their phones while 'boring stuff' is happening...
In olden days there would be a deacon with a long pole that would 'remind' the audience why they were in church...

A cell phone does have a minimal amount of traffic while 'not in use'. This is what the GSM noise was all about... it was the phone responding to the Mother Ship. In modern times the query/response signals continue, but are now such that they minimize interference with other equipment. The 'polling' is usually on the order of seconds, and rather 'minimal'... for some value of that word...

Active use would cause greater RF signals, more frequently, etc... but I think in order to be a significant issue the entire audience would have to be 'otherwise engaged'... a few 'teens' in the back twittering/facebooking... would probably not cause the type of interference you describe.
 
j1clark@ucsd.edu said:
In those frequencies cell phones should not have any impact on the noise floor, which is what may occur if you are operating in or 'near' the 700 MHz band which is now allocated to cell phone use in many areas.

In the olden days... and still in some cases the present... the GSM signaling method would cause sever noise in audio equipment... analog phones, audio playing equipment and of course during recording.

The 'noise' usually sounded like a clacking or chatter of short bursts of noise, very distinct.

If you say the audio 'drops out' that is not a symptom of GSM interference that I've heard of...

In the VHF 'high' TV band that you list, TV channels 7-13 operate, or 174 to 216 MHz. Don't know if there are any channels broadcasting in your area in that range... if you have an antenna based TV... run through channels 7-13...

There could be a mechanical cabling/connector issue that the preacher seems to elicit... and you don't... is the preacher active on stage/pulpit or just standing and delivering the sermon?

Contacts can also have issues if worn or the like.

This is the point that I'd get out my spectrum analyzer... and look at the frequency the device is operating on... but that's pretty expensive if you don't happen to have one around.

I did find this... http://www.ecrater.com/p/21650822/rf-spectrum-analyzer-using-dvb-t?gps=1&id=115931170339 ... for $17 it could be worthless junk... but it does use a TV tuner... and so would work in your bands of interest...
Click to expand...

Good info!

Are TV stations even broadcasting analog signals anymore? All of our TV stations come from the Charlotte area, which is a good 20 miles away at least. Though I don't know where they might have repeaters. There are some closer stations, but they are UHF. There are only 2 VHF stations in Charlotte. They are on channels 3 (generally the stronger of the 2) and 9. I do know that Channel 9 has some kind of field office here in my town, but I don't know if they do any over-the-air broadcasting from there or if it's just a satellite newsroom.

It is an interesting thought. But again, it would seem if a local TV station broadcast was disrupting our wireless, then it would be pretty much constant -- so it should manifest itself during my tests on weekdays as well. Shouldn't it?

When I test the mic and transmitter, I talk into it constantly while wiggling and twisting both the mic wire and the antenna wire every way I can think of. I've also used it with the wires in the exact position he uses them in -- wrapped around the Body-Pack, which is tucked into his inside jacket pocket. I know, not the ideal situation. But it even seems to work fine that way.

The max range of this system, under optimal conditions, is 300 feet. The distance the preacher is from the receiver is about 75 feet. So we should be well within the range parameters.

I wish I had a spectrum analyzer. That would be SO helpful! But like you, I doubt that $17 would be worth much.

The church has a few old tube analog TVs lying around. I can use one to see if any station is broadcasting in the channel 7 to 13 range.

I really appreciate you taking the time to help me figure this out. Thank you!
 
j1clark@ucsd.edu said:
Re: teens using their phones while 'boring stuff' is happening...
In olden days there would be a deacon with a long pole that would 'remind' the audience why they were in church...

A cell phone does have a minimal amount of traffic while 'not in use'. This is what the GSM noise was all about... it was the phone responding to the Mother Ship. In modern times the query/response signals continue, but are now such that they minimize interference with other equipment. The 'polling' is usually on the order of seconds, and rather 'minimal'... for some value of that word...

Active use would cause greater RF signals, more frequently, etc... but I think in order to be a significant issue the entire audience would have to be 'otherwise engaged'... a few 'teens' in the back twittering/facebooking... would probably not cause the type of interference you describe.
Click to expand...

What if those few teens were sitting right in front of the receiver? We have 3 teen girls -- sisters -- who like to sit on the very back row, right in front of where the camcorder and sound desk is located. I don't know if they use their phones during the service or not. I do know that they chat back and forth to each other during the congregation's singing of hymns -- because they're standing right in front of my camcorder when they do it. (They are quite tall.)
 
I'm going to upload a clip from last Sunday's sermon so you can hear for yourself what happens. I will also upload a clip from the previous Sunday, when the wireless performed flawlessly. Give me some time to get that done.
 
David W. Richardson said:
Doing further research, it appears that the Shure T1 Body-Pack transmitter operates on a VHF frequency range of 169.445 MHz to 216.000 MHz. The T4a receiver operates in a VHF range of 169.445 MHz to 240.000 MHz. The T4a receiver can also operate UHF in the range of 596 to 865 MHz. But since the Body-Pack transmitter can apparently only do the VHF 169.445 to 216.000 range, I assume we're okay on that, from a legal standpoint.
Click to expand...
Not necessarily... whilst the frequency range may be 169 MHz to 216, the actual frequency/channel is likely specific. (for instance 201.500 {or whatever}, so you may very well have incompatible channels. Most low cost and/or older VHS systems I've seen/used were a fixed frequency and could not be changed (at least not easily/cheaply). If you can find the specific operating frequency of your systems checking compatibility is easy.
Also.. antennas 'should' be relatively close the transmitter .. and 'line-of-site' with as few obstructions as possible, especially metal equipment enclosures, which I've encountered in many churches, hotel ballrooms and other venues.
AFAIK,he 169 to 240 MHz frequency range is FCC legal.
 
Okay, here is a 30-second clip of the beginning of the children's service last Sunday. The wireless mic drops out after the first few seconds. Once the mic drops out, what you hear of his voice and other sounds is being picked up by the pulpit mic, the choir mics or the piano mic.

https://youtu.be/Fb6hOt1AY0Y
 
Rick R said:
Not necessarily... whilst the frequency range may be 169 MHz to 216, the actual frequency/channel is likely specific. (for instance 201.500 {or whatever}, so you may very well have incompatible channels. Most low cost and/or older VHS systems I've seen/used were a fixed frequency and could not be changed (at least not easily/cheaply). If you can find the specific operating frequency of your systems checking compatibility is easy.
Also.. antennas 'should' be relatively close the transmitter .. and 'line-of-site' with as few obstructions as possible, especially metal equipment enclosures, which I've encountered in many churches, hotel ballrooms and other venues.
AFAIK,he 169 to 240 MHz frequency range is FCC legal.
Click to expand...

I will run to the church shortly and check to see the exact frequencies.

If you look at the video links I just posted, it will give you a good idea of distance, orientation, and what is between him and the receiver.

We may have to place the receiver at the front of the church, perhaps under the pulpit if there's room. Running an XLR cable under the floor, the length of the sanctuary, to get it connected to the mixer isn't ideal. But we do what we have to do.
 
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