Can cell phones interfere with wireless mic?

"What is a shark fin antenna setup"?
External 'shark fin' log periodic antennas are a common option for medium and high priced UHF receivers, and external antenna systems were available for VHF systems. Even an external whip antenna or homemade coat-hanger wire antenna would help if proximity and/or line-of-sight to the transmitter is the issue. Trouble is.. most low cost receivers do not have an external antenna option.
 
Rick R said:
"What is a shark fin antenna setup"?
External 'shark fin' log periodic antennas are a common option for medium and high priced UHF receivers, and external antenna systems were available for VHF systems. Even an external whip antenna or homemade coat-hanger wire antenna would help if proximity and/or line-of-sight to the transmitter is the issue. Trouble is.. most low cost receivers do not have an external antenna option.
Click to expand...

Yeah, ours doesn't have an external antenna connector.

Okay, I went to the church and checked. Both the transmitter and receiver operate at 171.845 MHz. So at least we know that.

I re-tested the wireless mic. So far it still works fine -- in the empty sanctuary.
 
I found this info on a website earlier, relating to cell phone interference problems...

"Phasing out the problem

Cell phone and WiFi interference is no longer an issue for most professional microphones manufactured since 2006. Shure and Audio Technica, for example, both report that they have completely eliminated this kind of mic interference.

You may still run into an issue, however, with lower-cost mics or microphones that have been sitting in a dealer’s warehouse. Shure, for one, has not changed any model numbers, but instead phased in the shielding as they sold out their inventories."

So it sounds like the problem was resolved with shielding. Is it possible for me to put shielding on the gear we have? And if so, how?
 
The YouTube clip at the bottom demonstrates exactly what cell phone (specifically GSM) interference sounds like.

It seems quite possible that you are experiencing RF "shading" from the mass of bodies between the transmitter (the pastor sitting on the steps with the kids) and the receiver (in the back of the sanctuary). Repeating: The solution is to get the receiver up at the front, as close to the transmitter as practical. Perhaps even under the first pew in the congregation seating area. Is the same microphone used for the "main event" (the sermon/homily)?

All analog terrestrial TV broadcasting in the US became illegal on 01-Sep-2015. But it is rather a moot point. For the purposes of this discussion TVRFI is TVRFI whether it is analog or digital. But it doesn't sound like the problem is TVRFI since TV stations generally run 7x24, including during the periods when the system was tested.

We must assume that you had TRULY FRESH batteries in the transmitter (and receiver?) Remember that many transmitters, especially older ones, do poorly with rechargeable batteries because even when fully charged, they look like a half-dead primary cell as far as the transmitter is concerned. (1.2V vs. 1.5V) Newer wireless transmitters are designed to accommodate the lower rechargeable voltages more gracefully.

Please note that the most common GSM interference is NOT in the wireless mic receiver. Many people find it surprising that it is the unbalanced wire between the microphone capsule and the transmitter body pack that is the most susceptible to cell phone interference. ESPECIALLY when the person wearing the transmitter has an active phone in their pocket probably only inches away. Cell phones put out a rather strong RF signal (orders of magnitude greater than wireless mics). So it is not surprising that the RFI can sneak into the transmitter body pack through the mic cable.

Professional operations with A3 audio assistants ("mic wranglers") not only have the wrangler confirm fresh batteries, and coordinate mic channels, but also relieve the presenter of his/her cell phone so that it doesn't interfere with the presentation (either electrically or socially).

Cell Phone (GSM) interference.
https://youtu.be/f9nOqTN10Lk
 
Richard Crowley said:
The YouTube clip at the bottom demonstrates exactly what cell phone (specifically GSM) interference sounds like.

It seems quite possible that you are experiencing RF "shading" from the mass of bodies between the transmitter (the pastor sitting on the steps with the kids) and the receiver (in the back of the sanctuary). Repeating: The solution is to get the receiver up at the front, as close to the transmitter as practical. Perhaps even under the first pew in the congregation seating area. Is the same microphone used for the "main event" (the sermon/homily)?

All analog terrestrial TV broadcasting in the US became illegal on 01-Sep-2015. But it is rather a moot point. For the purposes of this discussion TVRFI is TVRFI whether it is analog or digital. But it doesn't sound like the problem is TVRFI since TV stations generally run 7x24, including during the periods when the system was tested.

We must assume that you had TRULY FRESH batteries in the transmitter (and receiver?) Remember that many transmitters, especially older ones, do poorly with rechargeable batteries because even when fully charged, they look like a half-dead primary cell as far as the transmitter is concerned. (1.2V vs. 1.5V) Newer wireless transmitters are designed to accommodate the lower rechargeable voltages more gracefully.

Please note that the most common GSM interference is NOT in the wireless mic receiver. Many people find it surprising that it is the unbalanced wire between the microphone capsule and the transmitter body pack that is the most susceptible to cell phone interference. ESPECIALLY when the person wearing the transmitter has an active phone in their pocket probably only inches away. Cell phones put out a rather strong RF signal (orders of magnitude greater than wireless mics). So it is not surprising that the RFI can sneak into the transmitter body pack through the mic cable.

Professional operations with A3 audio assistants ("mic wranglers") not only have the wrangler confirm fresh batteries, and coordinate mic channels, but also relieve the presenter of his/her cell phone so that it doesn't interfere with the presentation (either electrically or socially).

Cell Phone (GSM) interference.
https://youtu.be/f9nOqTN10Lk
Click to expand...

This is excellent information. Thanks Richard!

My first thought has always been the bodies. But as I said, last Sunday I lifted the receiver up high enough to get a direct line-of-sight between the two, without bodies in between. It made no difference. Furthermore, there have been days when the church was pretty full, but the wireless performed flawlessly. In our church, most of the regular members sit in the same spot in the same pew week after week. All of those things make the human bodies seem less likely to be the problem, although they still could be. I have no real way of testing that out.

Nearly all of the sermon is done using the wired mic mounted in the pulpit. Generally only the children's sermon -- about 5 minutes -- is done with the wireless. The preacher turns it on right before he needs it, then switches it off 'mute' when he's ready to use it. Then he turns it off again when he's done.

We never use rechargeable batteries. The 'low battery' light on the body pack isn't glowing. The receiver runs off AC power, so no batteries there.

I think in all likelihood the flaw in the system is the cable between the body pack and the mic. You said 'unbalanced' -- is there a chance you meant 'unshielded'? I could see a lack of shielding being a problem when it comes to RF interference.

There is a good possibility that the preacher carries a cell phone during the service. I will ask him about that. Maybe I can do another test tomorrow with my own cell phone resting close to the body pack. That could very well be the problem.

Thanks again for all your help!
 
After the children's service last Sunday, there was a baptism done. This is one of the few other times this wireless mic is used.

Instead of just dead silence, there was some intermittent static-y sound, though it doesn't sound like the sample Richard gave of GMS interference.

Here's the clip -- https://youtu.be/n2Fw5IWt8IU
 
Your sample shows the classic symptoms of low signal strength.
The bodies of the congregation don't have to be DIRECTLY between the transmitter and receiver. They can still soak up RF.

If I didn't believe that betting was immoral, I would wager 10:1 that the problem is simply low signal strength.
I keep suggesting moving the receiver to the FRONT of the sanctuary, but you have never acknowledged that suggestion.
Even if you have to temporarily run a mic cable up to the front for the receiver, it would be worth the experiment, IMHO.
 
Richard Crowley said:
Your sample shows the classic symptoms of low signal strength.
The bodies of the congregation don't have to be DIRECTLY between the transmitter and receiver. They can still soak up RF.

If I didn't believe that betting was immoral, I would wager 10:1 that the problem is simply low signal strength.
I keep suggesting moving the receiver to the FRONT of the sanctuary, but you have never acknowledged that suggestion.
Even if you have to temporarily run a mic cable up to the front for the receiver, it would be worth the experiment, IMHO.
Click to expand...

Richard, I myself said that we may have to move the receiver to the front, perhaps under the pulpit, in order to resolve the problem. I also said it would not be easy to run an XLR cable under the floor to the back of the sanctuary to connect the receiver to the mixer. It also complicates troubleshooting future problems if I can't see the signal indicator lights or change the output volume level or move the antennae when a problem occurs. So for those reasons, that's really a last resort.

Explain to me why, in the exact same scenario -- sitting in the same spot, with most of the same people sitting where they do -- for two Sundays in a row the wireless worked flawlessly?

I'm not disagreeing that it's likely the warm bodies are soaking up RF -- I just have no way to test it without a full sanctuary of people who all leave their cell phones and other devices outside and let me practice with the equipment. So I'm hoping against hope that the problem lies somewhere else, that it can be found, and that it can be resolved.

But if all other possibilities are exhausted and I have no other choice, then I certainly will move the receiver to the front.
 
David W. Richardson said:
Explain to me why, in the exact same scenario -- sitting in the same spot, with most of the same people sitting where they do -- for two Sundays in a row the wireless worked flawlessly?
Click to expand...

With RF one has to imagine that one is in a 'cave' with several(many) side tunnels... and the person speaking is somewhere in the tunnel system, and someone listening at some fixed point. As the speaker moves back into the 'cave' there are more pathways for their sound to reach the listener... but since there are many pathways, it can be the case that the speaker's voice arrives at slightly different times, and so, there is a 'jumble'
at the listener's point... as the speaker moves closer to the listener, the pathways reduce, or, the amount of 'energy' from a given 'non-line-of-sight' pathway becomes less, and the listener is able to then sort out the words (signal) of the speaker.

On the other hand one of the 'alternate pathways' could produce a clearer 'signal' for some given arrangement of speaker and 'pathways'...

There is a concept of constructive and destructive interference, where a signal by some 'pathway' reaches the listener's point 180 deg. out of phase with the 'original' signal, and reduces the signal (voice) by some amount...

Imagine now placing 'padding'(aka bodies in a church...) in some set of the tunnels... one the would change the characteristics of the pathways...

----

Given you say the preacher has the antenna on his back, his body can act as an absorber, and one may in fact be receiving a a reflected signal, that bounces through the 'cave'(nave... in cathedral parlance...) of the church to the receiver. If the church has steel reenforcements, or the like, these also act as reflectors...

Some times problems are due to a complex set of circumstances... other times they are due to some very simple things... like bad connections, broken conductors in otherwise 'good looking' cables... junctions between cable and connector that 'look good' but are in fact broken... etc.

It is a tedious process of elimination to find the culprit(s), because there can be multiple problems which just hide one another.
 
Unfortunately, inexpensive "pro-sumer" grade wireless receivers don't give us any helpful information like signal strength indication.
Or frequency tuning. So the best we can do is to make relative diagnosis by the symptoms.

There are also combinations of causes where even out-of-band RFI (from cell phones or whatever) can make the receiver LESS sensitive to the operating frequency.
People who use wireless mics in big cities (and especially in NY, LA, SF, Chicago, etc.) call them "RF Hell" for a reason.
Most of the professionals there have RF spectrum analyzers just so that they can see the "big picture" what is going on around them.
And by "around them" I mean both physically, and RF-wise.
They sometimes must change channels several times a day to keep operating cleanly.

It also seems well within the realm of possibility that either the transmitter and/or the receiver may have drifted.
And/or the receiver tuning/alignment may simply be suffering from old age and marginal design/construction/components.
There are procedures for "tuning up" the transmitter/receiver to operate together, but alas, the service information for those
kinds of products are difficult-to-impossible to acquire, if they were even published at all beyond factory assembly processes.

Your description of the symptoms, your explanation of your experiments, as well as the sample clip still make me think that signal-strength is the prime suspect.
 
Okay, I got all of that -- I think. I can see how warm bodies could soak up the RF. And I'm guessing the high vaulted ceiling doesn't help either, since it doesn't give the signal a convenient reflective surface.

Obviously, moving the receiver to the front would negate that problem. But would mounting the receiver up high on a back wall also work? Would it be true that the higher the receiver is placed, the less the warm bodies are going to compromise the signal? Or is that just a pipe dream?

BTW, I don't know where I said that the preacher has the antenna on his back. Actually, the body pack is in his front left jacket pocket. So the antenna is in his front. I did do an experiment where I turned my back to the receiver, putting my body between the transmitter and receiver. That, of course, accomplished nothing.

Signal drift over time sounds like a possibility. Although it doesn't seem to explain why it works perfectly for a week, doesn't work for 2-3 weeks. Works perfectly for 2 weeks, then doesn't work the next week. I would think if the age of the gear was causing signal drift, it would be pretty constant. But maybe I'm wrong on that. If it was signal drift, it sounds like replacing the gear is needed.

To be honest, I am more and more leaning toward your theory that the problem is simply the number of warm bodies in the pews absorbing the RF. That certainly makes sense, and it seems to fit the audio examples I posted.

It also occurs to me that, while the preacher doesn't use rechargeable batteries in the transmitter, he may use cheap battery brands, perhaps even carbon batteries rather than good alkalines. I know he doesn't use a fresh battery every week. I mentioned that the 'low battery' light isn't on, but it could be that light doesn't work. Maybe the battery is low. Or just not strong enough to do the job. I'm going to go buy some fresh Duracell 9-volts and see if they make a difference.

Thanks again for all your help, Richard. It's much appreciated.
 
David W. Richardson said:
Okay, I got all of that -- I think. I can see how warm bodies could soak up the RF. And I'm guessing the high vaulted ceiling doesn't help either, since it doesn't give the signal a convenient reflective surface.

Obviously, moving the receiver to the front would negate that problem. But would mounting the receiver up high on a back wall also work? Would it be true that the higher the receiver is placed, the less the warm bodies are going to compromise the signal? Or is that just a pipe dream?
Click to expand...

You can try it, but given the marginal operation suggested by the symptoms, it is a significant compromise.

BTW, I don't know where I said that the preacher has the antenna on his back. Actually, the body pack is in his front left jacket pocket. So the antenna is in his front. I did do an experiment where I turned my back to the receiver, putting my body between the transmitter and receiver. That, of course, accomplished nothing.
Click to expand...
You have already demonstrated that your weekday tests don't very well predict how the system will perform in Prime Time on Sunday.
I don't remember if you identified the wireless system, or whether the transmitter has an external antenna (a loose wire, etc.) Body packs with a trailing wire antenna frequently suffer by the antenna being folded/crunched while putting the pack into a pocket. Much better to clip the transmitter onto the user's belt and let the antenna wire trail freely. And the physically closer the antenna is to the body, the more of the transmitted signal gets soaked up by the user's body.

Signal drift over time sounds like a possibility. Although it doesn't seem to explain why it works perfectly for a week, doesn't work for 2-3 weeks. Works perfectly for 2 weeks, then doesn't work the next week. I would think if the age of the gear was causing signal drift, it would be pretty constant. But maybe I'm wrong on that. If it was signal drift, it sounds like replacing the gear is needed.
Click to expand...
The bottom line is that it shows it is operating in a MARGINAL part of its operating range. Depending on varying ambient conditions, sometimes conditions are good enough to operate OK, and sometimes it is just overcome by the situation: weakening transmitter power, decreased receiver sensitivity or selectivity, and unknown RF interference.

To be honest, I am more and more leaning toward your theory that the problem is simply the number of warm bodies in the pews absorbing the RF. That certainly makes sense, and it seems to fit the audio examples I posted.
Click to expand...
If the system weren't marginal, the number of bodies in the pews wouldn't make a significant difference.

It also occurs to me that, while the preacher doesn't use rechargeable batteries in the transmitter, he may use cheap battery brands, perhaps even carbon batteries rather than good alkalines. I know he doesn't use a fresh battery every week. I mentioned that the 'low battery' light isn't on, but it could be that light doesn't work. Maybe the battery is low. Or just not strong enough to do the job. I'm going to go buy some fresh Duracell 9-volts and see if they make a difference.
Click to expand...
Your team should be responsible for providing and installing (and replacing) the batteries. Your preacher has enough other things to worry about. Give him a break.
 
Richard Crowley said:
You can try it, but given the marginal operation suggested by the symptoms, it is a significant compromise.
Click to expand...

I had thought this might reduce the impact of warm bodies on the RF signal. Would it not?

I don't remember if you identified the wireless system, or whether the transmitter has an external antenna (a loose wire, etc.)
Click to expand...

I identified the system as a Shure with Body Pack T1-W and receiver T4a-W. The transmitter certainly does have an external antenna.

Body packs with a trailing wire antenna frequently suffer by the antenna being folded/crunched while putting the pack into a pocket. Much better to clip the transmitter onto the user's belt and let the antenna wire trail freely. And the physically closer the antenna is to the body, the more of the transmitted signal gets soaked up by the user's body.
Click to expand...

Although he had been wearing it inside his jacket pocket, I learned this morning that for the last several weeks he's had it clipped to his belt, although he doesn't like it there.

The bottom line is that it shows it is operating in a MARGINAL part of its operating range. Depending on varying ambient conditions, sometimes conditions are good enough to operate OK, and sometimes it is just overcome by the situation: weakening transmitter power, decreased receiver sensitivity or selectivity, and unknown RF interference.
Click to expand...

Okay. So as I said, I increased the gain on the transmitter and reduced the squelch on the receiver. I will put a fresh Duracell 9-volt battery into the transmitter for this Sunday's service.

If the system weren't marginal, the number of bodies in the pews wouldn't make a significant difference.
Click to expand...

Okay, so what are we saying here? What are the things I can reasonably do to make the system less marginal? Or are there any, aside from moving the receiver to the front of the church? Which, as I've repeatedly said, I'm willing to do if there is no other choice.

Your team should be responsible for providing and installing (and replacing) the batteries. Your preacher has enough other things to worry about. Give him a break.
Click to expand...

Ideally. But he keeps the transmitter body pack in a drawer in his locked office. It's sometimes not easy to get access to it. Which is why he has always been the one who changes the batteries. But we can develop a protocol for that.
 
I'm not familiar with that Shure system, but some VHF transmitters have a relatively long dangling wire antenna (typically around 14 inches long for 5/8 wave) Others used the mic cable itself as an antenna.. So if this is the case, and as Mr. Crowley stated, if the mic's cable is balled up in the wearer's pocket and not extended, this can reduce RF transmission.
PS- David, you also mentioned a VHF Nady assistive listening system. What frequency is that tuned to, or does it make a difference if it's shut down?
 
Rick R said:
I'm not familiar with that Shure system, but some VHF transmitters have a relatively long dangling wire antenna (typically around 14 inches long for 5/8 wave) Others used the mic cable itself as an antenna.. So as Mr. Crowley stated, alternately if the mic's cable is balled up in the wearer's pocket and not extended, this can reduce RF transmission.
PS- David, you also mentioned a VHF Nady assistive listening system. What frequency is that tuned to, or does it make a difference if it's shut down?
Click to expand...

The T1 Body-Pack has a separate antenna cable. Not sure how long it is, but I don't think it's 14".

The Nady ALD-800 operates in the range of 72-76 MHz, so I don't think there's a problem. And no, whether it is turned on or off seems to make no difference.
 
If we do have to move the receiver to the front of the church, Amazon has a pair of 50' balanced XLR cables for $39.99, with free shipping (Prime). That's doable -- although this is still a last resort.
 
Do a test prior to spending the $$$.
Secondly, for $39.99, I would choose Canare Star-Quad Markertech 50' Canare Star-Quad. I have 25+ yr. old Canare cables that have been subject to all kinds of ENG abuse and still work. You could get lower cost cables designed for fixed installation if $$$ is a big issue.
 
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