N/A, FM antenna question, FM neck-loop

[Brad W]

I have this FM receiver. It's a neck-loop device that interfaces with my hearing aids through the teli-coil function. It's a small box that hangs like a pendant around my neck, the "neckless" being the t-coil magnetic transmitter emitter.

This receives an FM radio signal, 72 MHz. I use it in church, where they re-transmit the audio from the microphones to my hearing aids.

The church's transmitting antenna is in a rack room closet on the other side of the church from where I normally sit, and the signal is just a little too weak. I get a lot of static.... but I've found that if I hold the box the signal clears up. I've suggested they might consider moving the antenna out for better coverage, but that isn't happening.

It's Kinda like holding the rabbit ears on the TV when I was a kid.
So I'm trying to understand what is changing in the antenna system when I hold the case?....or more to the point what can I do to boost the antenna reception? I was thinking about playing with putting an aluminum reflector plate behind the box...something like that.
but
after opening it up I see nothing that looks like an antenna to me...but I'll admit to not knowing what I'm looking at in electronic devices.... anyway, maybe the antenna is in the neck loop wire and not in the box at all....
but if that's the case, why does the reception improve when I hold the box?

The first picture is from the manufacturer's web page showing it worn. The model is using an optional earbud that plugs into the bump on the neck loop wire. I don't need to use that...Like I said I'm using the magnetic signal that comes from that wire.​

2nd picture shows the back with the belt clip removed and the battery cover removed​

3rd picture shows the battery pulled out... Li-Ion​

4th picture shows the circuit board, The orange ribbon cable to the left is what connects to the display and buttons on the front face. This board faces out when worn​

5th picture shows the black model number number sticker that's stuck to the back side of the circuit board. The same sticker you can see when the battery is removed. This faces my chest when worn.​

This

 

[RussR]

At the risk of asking the obvious, rather than the effort trying to modify the device, why don't you just sit on the other side of the church, closer to the transmitter?

 

[Kelvin]

I am a dealer for Listen.
Decent gear.
Great support. Don't hesitate to call them for insight.

My 2 cents worth:
Move the antenna to a more favorable location by extending the coax.

 

[Tools]

Antennas are very esoteric devices…. riddled with “complex reactance”.

Unless ya really know what kind of antenna it is, you’re just guessing.

What we do know is that you hanging onto a portion is changing the capacitance somehow… really about all ya can do is experiment. How sweaty your palms are is likely gonna matter more than tin foil anywhere.

If holding helps, and it usually hangs around your neck… can ya put it under your shirt against your skin? Hehe, may have to shave some chest hair.

There are electrical engineers here that should be along shortly to give more better advice!!

Good news, nearly nil chances of hurting anything. Bad news, I can tell ya from a stress ekg test I took once that chest hair shaving thing is gonna itch… BAD.

 

[GeorgeC]

I'm not an rf person or even a ham, but I have a similar thing going on here.

I live a few miles away from a 75kW FM tower. I should be able to hear it in my fillings. I have a little radio that works better a) in certain orientations and b) if I'm holding it.

Guesses:
* The signal is way too loud and is overwhelming the frontend.
* Orientation matters because aiming the (chip?) antenna null in the right direction will attenuate the signal.
* Holding it also attenuates the signal.

I don't know. Radio is PFM.

 

[flyingron]

I got quite a start when travelling recently. I forget where it was (possibly Heathrow). Going through security, their instruction announcements started coming across direct to my hearing aids. First time I've ever seen that.

 

[Brad W]

At the risk of asking the obvious, rather than the effort trying to modify the device, why don't you just sit on the other side of the church, closer to the transmitter?

ha ha

my only response is
I tried that, but my wife doesn't like sitting over there. I can't understand why.
Maybe she takes pleasure in knowing that I have static in my ears
Or maybe she just doesn't like it when I hear what the priest has to say....

 

[Brad W]

I am a dealer for Listen.
Decent gear.
Great support. Don't hesitate to call them for insight.

My 2 cents worth:
Move the antenna to a more favorable location by extending the coax.

That was the first thing I tried asking for....but I guess the audio guy isn't interested in extra work.
Truthfully, there probably aren't many people who use the system, so arguably not worth the effort and expense perhaps...
and bouncing back to Russ' suggestion....that's the first thing he suggested too!

 

[Brad W]

I got quite a start when travelling recently. I forget where it was (possibly Heathrow). Going through security, their instruction announcements started coming across direct to my hearing aids. First time I've ever seen that.

Sounds like maybe a looped room or looped area and you have T-Coil mode turned on
I'm coming up on 3 or 4 years now with these things and have yet to find one of those looped rooms. I understand it's much more common to have them over in Europe.

I sure do wish they would loop our church. I don't think it costs all that much to do, but would be a bit more trouble since it's already built.
and besides, the more modern and probably more useful approach would be to ditch the old T-Coil tech altogether and install a Bluetooth system instead

 

[Brad W]

I am a dealer for Listen.
Decent gear.
Great support. Don't hesitate to call them for insight.

My 2 cents worth:
Move the antenna to a more favorable location by extending the coax.

maybe I'll look up the number and do that this afternoon. Thanks

 

[Mikey52]

What if you put a 12"x12" piece of aluminum foil behind it on your chest, like a bib.

 

[KE5BM]

I'm not an rf person or even a ham, but I have a similar thing going on here.

I live a few miles away from a 75kW FM tower. I should be able to hear it in my fillings. I have a little radio that works better a) in certain orientations and b) if I'm holding it.

Guesses:
* The signal is way too loud and is overwhelming the frontend.
* Orientation matters because aiming the (chip?) antenna null in the right direction will attenuate the signal.
* Holding it also attenuates the signal.

I don't know. Radio is PFM.

Ham here. That's exactly the problem. The only fix is to use an attenuator of some sort. Guessing your radio doesn't have an external antenna connection so wrapping the radio (or at least the back side of it) in some sort of material that will reduce the signal strength will help. Aluminum foil might be a bit extreme but it'll do the job.

 

[KE5BM]

I have this FM receiver. It's a neck-loop device that interfaces with my hearing aids through the teli-coil function. It's a small box that hangs like a pendant around my neck, the "neckless" being the t-coil magnetic transmitter emitter.

This receives an FM radio signal, 72 MHz. I use it in church, where they re-transmit the audio from the microphones to my hearing aids.

The church's transmitting antenna is in a rack room closet on the other side of the church from where I normally sit, and the signal is just a little too weak. I get a lot of static.... but I've found that if I hold the box the signal clears up. I've suggested they might consider moving the antenna out for better coverage, but that isn't happening.

It's Kinda like holding the rabbit ears on the TV when I was a kid.
So I'm trying to understand what is changing in the antenna system when I hold the case?....or more to the point what can I do to boost the antenna reception? I was thinking about playing with putting an aluminum reflector plate behind the box...something like that.
but
after opening it up I see nothing that looks like an antenna to me...but I'll admit to not knowing what I'm looking at in electronic devices.... anyway, maybe the antenna is in the neck loop wire and not in the box at all....
but if that's the case, why does the reception improve when I hold the box?

The first picture is from the manufacturer's web page showing it worn. The model is using an optional earbud that plugs into the bump on the neck loop wire. I don't need to use that...Like I said I'm using the magnetic signal that comes from that wire.​

2nd picture shows the back with the belt clip removed and the battery cover removed​

3rd picture shows the battery pulled out... Li-Ion​

4th picture shows the circuit board, The orange ribbon cable to the left is what connects to the display and buttons on the front face. This board faces out when worn​

5th picture shows the black model number number sticker that's stuck to the back side of the circuit board. The same sticker you can see when the battery is removed. This faces my chest when worn.​

This

It does appear that the antenna is probably embedded in the neck loop. I doubt there is a simple way to improve the antenna's reception. It's possible, though that one of those potentiometers can be adjusted to improve the gain of said antenna which would do the trick. Looks like they're labeled C10, C38, and C23 but it's hard to be sure looking at that picture. Perhaps with a copy of the schematic it could be determined which one controls gain. Hopefully the nice folks at Listen would be willing to tell you which one/how to make adjustments.

Edit: Manual shows that the reception is provided through the headphone wire. Perhaps if you try using just a straight headphone without the loop, the antenna then becomes vertical instead of loop. This would likely match the transmit antenna and provide slightly better reception. Also, to answer your question...holding the device causes a sort of capacitance relation with the device. So basically, it's able to use your body as part of the antenna system. I'm guessing you're quite a bit larger than the wire loop so your device gets the benefit of extra reception surface area.

 

[Albany Tom]

First, having trouble understanding why the church people aren't being more helpful. In my experience, they're there to serve you, not the other way around, so at the risk of being insensitive, I might look for better people. Sorry if that sounds harsh.

As far as the technical parts go, it could be a couple of things. It could be that something within that room is coupling with the antenna, and de-tuning it, and the signal isn't getting out as well as it should be. To test that, ask if they can move the antenna around a little bit within the room. Next, there could be different spots in the room that have different coverage, OR you could be getting reflections that are negatively interfering with the primary signal. To test this, walk around in different places and see how the signal changes. At 72 MHz, moving a few feet either way could change things. Next, there could be something wrong with the transmitter or antenna. Easy enough to test is someone has a forward/reflected power meter they can put in between the two. A local ham could help with that. Next, as others have pointed out, a very strong local FM or pager transmitter could be overloading, or "desensing" your receiver. That could be fixed by a filter, if you can identify the signal source frequency.

The receiver antenna, to me, is weird. There is a technique for close range direction finding in the VHF range called "body blocking", where you hold the handheld receiver right against your chest, and listen. Signals from the front are stronger than from your back, because you as a person absorb some of the RF. Not the most precise thing in the world, but it does work. 72 MHz is kinda similar frequency...so you might try standing up and pointing in different directions to see what works better. Oh, and standing up is almost certainly going to be better than sitting down, and standing on the pew even better than that.

So... long story short, if you find out that you get good reception standing on the pew pointed 60 degrees to the right of the direction of the preacher, but in the section your wife likes, that MIGHT be enough to convince her you guys should sit in a different part of the church. If you do this, post pictures.

Oh, one more..if the church audio guy fastened the transmit dipole antenna to a metal rack, you have my permission to slap him for being clueless. And if they're using a 4" long "rubber duck" antenna instead of a dipole for 72 MHz, same thing.

 

[Bill]

why don't you just sit on the other side of the church, closer to the transmitter?

You’ve never been to church have you?

 

[RussR]

First, having trouble understanding why the church people aren't being more helpful. In my experience, they're there to serve you, not the other way around, so at the risk of being insensitive, I might look for better people. Sorry if that sounds harsh.

To be fair to the church's tech people, I can see the conversation going something like this:

OP: My receiver doesn't work well when I sit way over here.
Tech: I'm sorry to hear that, have you tried sitting over there?
OP: Yes, and it works great over there!
Tech: Great! It is a pretty low-powered transmitter, and this is a big church, so that happens. But problem solved, just sit over there.
Op: But my wife doesn't like that side.
Tech: Um, okay, I'm not sure what you want us to do.

OP, I'm just having fun. I know you're trying to respect your wife's desires to sit on the one side. But I'm not sure what another "realistic" solution is that doesn't require a lot of time or effort on your part, or a lot of time and money on the church's part.

This has been answered already, but when you hold the device the presence of your hand causes some capacitive loading on the antenna - this can change the tuning of the antenna and possibly the directionality of it. Which affects the reception, sometimes for better in a certain case. Same effect with rabbit-ear TV antennas.

Maybe show up like this next week?

 

[RussR]

You’ve never been to church have you?

Sure, but I'm not sure what you're getting at. I know that lots of people have their preferences on where to sit. Same pew every week. People get in ruts. Routines. But I'd like to think that making sure everybody in attendance can hear the sermon would override that.

 

[SoonerAviator]

I wonder if you shouldn't ask again to see if they could just move the transmitting antennae out into the open if they're currently shoved in an audio rack or similar. The audio guy you talked to may not know anything about it, or just forgot to check in about it.

 

[flyingbrit]

OP, looking at Listen's literature it appears they have two 72MHz transmitter models, one with a vertical whip for smaller buildings and one with a horizontal dipole for larger buildings. I will assume you have the dipole since there is talk about moving it.

They may be unwilling to move the antenna into the main room because they think it is unsightly. Some people are weird that way!

First, is the antenna pointed the right way? A dipole will transmit best in a broadside direction, with nulls at either end. (Figure 8 pattern).

Second, is the antenna near any metal, like the rack(s)? Ideally, it should be at least 4 feet or so away. Perhaps it could be mounted from the closet ceiling (keep distance from suspended ceilings) or the wall. It probably does not matter much whether it is vertical or horizontal given the shape of the receiving antennas.

 

[Brad W]

thanks everyone!

I called Listen's tech support yesterday afternoon. Nice guy and seemed to take the time to try to help, but didn't really have much for me....

Learned, like someone else pointed out here, that the antenna for the receiver is the ground conductor in the neck loop. I wish I'd have thought to ask how that works with it connected into two jacks...and if the thing is directional, or "handed". Maybe that little lump ( I think it's an amplifier or something) that's in the neck loop is a termination of sorts for the antenna so only one side of it is active.. (??)

I did ask him what is happening when I held the box to improve the signal...AND if the antenna is in the loop, how does holding the box change it? (remember the old rabbit ear antennas and you touched the actual antenna to improve the signal, not the TV box!) He had no answer...

He did suggest that if the transmitter is in a rack room, it's probably what he called their "low-end" antenna...and that it's directional so maybe moving it around might help. @flyingbrit, I think the only talk about moving the antenna was from me suggesting that it would probably be better if he moved it out of the closet. I really don't know how practical that would be.

I think I'll reach back out to the AV guy at church

 

[Bill]

Sure, but I'm not sure what you're getting at. I know that lots of people have their preferences on where to sit. Same pew every week. People get in ruts. Routines. But I'd like to think that making sure everybody in attendance can hear the sermon would override that.

You would think, but some are very insistent when it comes to sitting in “their” spot.

 

[Brad W]

yeah, some are funny about their spot. I can get a little twinge of that about my parking spot at work for some reason that I can't understand.....
We're not that specific about our spot in church.... pretty much anywhere in the South Transept works for us. I personally would prefer anywhere in the Nave, but we started sitting over there in the transept when the kids were little because it felt a little less 'out of the way' so that became my wife's habit.
We don't like the North transept at all, where I'd have to sit to be closer to the transmitter. I think it's because the choir box is over there and it just seems like all that infrastructure is in the way and disconnects us from the service. It feels 'anti-fung shui' over there, if you're into that sort of thing.