FM radio heard through Clearcom Headset System

[Paul V123]

Headset System
We have an FM radio station coming through our Clearcom headset system. Below is what we have tried.

We checked all connections and fixed the few connections that needed to be fixed.
We pulled the each station one at a time out of the system in hopes of finding the culprit.
Once every station except for one was disconnected and we still had the radio we pulled that
station and went to another station in case our test station was the culprit and it was not.

We tried grounding the three matrix units together then to a water pipe ground.
We lifted the AC ground.
We lifted pin #1
We switched the plugging in the power supplies to rule them out.
We tried many different mic cables. We tried different brands of mic cables.
We tried Clearcom belt packs series 500, 600, and a very early metal boxed model. Tried Production Advantage belt packs.
Took the power supplies out of the rack then moved the power supply away from the rack, plugged the power supply in and connected one belt pack, headset to it. In other words, it was one power supply and one belt pack and one headset. Then tried a different cable, belt pack, and headset. Tried a different AC circuit that had its circuit in the sound booth (nowhere near when it had been circuited.)

Tried a brand new power supply which was also a new model with one belt pack, cable, and headset and switched the belt pack, cable and headset.
Called the radio station and they were a bit baffled but offered to come over and see if they can come up with a solution.
Plugged the power supply though and APC with just one belt pack, one cable, and one headset. Then unplugged the AC power so the power supply was now operating on the battery backup only (it was no longer running on true AC electricity.)
Tried to put an active DI in line(I know crazy idea but grasping at straws.)
Took the power supply over to the a nearby building and plugged it into their electricity with one belt pack, one cable and one headset and we replicated the problem.
October 17, 2016 Engineer from radio station came over and tried toriods. No success. Showed us the radio stations antenna which is about 200 yards away.

 

[coldnorth57]

I have had this happen and found a bad solder joint(in a conduit box), I was lucky i only had two legs in the system so it was easy to zero in on the fault.

What Main station are you using ? Can you separate the different runs (in the wall)?

 

[FMEng]

These situations can be difficult, but not impossible to fix. I am pretty sure this can be resolved, or at least reduced, with toroids, but the station engineer may not have used the right type, or didn't put them in the correct places. I will elaborate more when it isn't so late.

 

[Van]

Air-gap somewhere or the radio tower has faulty shunts. Typically AM is a bigger issue.
I'm assuming the radio is present no matter which physical headset you are using, a Bad solder on the ground or Shield can cause this issue.
Here's one more test to try. when you have the headset on and can hear the FM signal, turn the volume up and down. does it get louder and softer or does it stay more constant. This will help isolate whether your issue is in the base end or in the pack end. Did messing with the "Side tone" trim do anything to alleviate the issue?

 

[Paul V123]

I have had this happen and found a bad solder joint(in a conduit box), I was lucky i only had two legs in the system so it was easy to zero in on the fault.

What Main station are you using ? Can you separate the different runs (in the wall)?

I have had this happen and found a bad solder joint(in a conduit box), I was lucky i only had two legs in the system so it was easy to zero in on the fault.

What Main station are you using ? Can you separate the different runs (in the wall)?

We pulled the Main Station out of the system at one point and went directly from power supply to belt pack to headset so, we were not using the main station at all. We were not using any lines run through any conduit or anywhere else and we still had radio. We took the power supply and headset to a different building in the neighborhood and still had radio.

 

[Paul V123]

Air-gap somewhere or the radio tower has faulty shunts. Typically AM is a bigger issue.
I'm assuming the radio is present no matter which physical headset you are using, a Bad solder on the ground or Shield can cause this issue.
Here's one more test to try. when you have the headset on and can hear the FM signal, turn the volume up and down. does it get louder and softer or does it stay more constant. This will help isolate whether your issue is in the base end or in the pack end. Did messing with the "Side tone" trim do anything to alleviate the issue?

Correct, we tried different cables, belt packs, and headsets. The radio remained. The volume sometimes get louder with volume. Sometimes the mic must be activated to hear the radio but sometimes not. I occasionally change the side tone but did not try in troubleshooting this situation. I will try and see if that helps. Thank you.

 

[JD]

We took the power supply and headset to a different building in the neighborhood and still had radio.

Does this station have a transmission facility right in town? Pretty extreme! You may want to try making up a filter box. Basically, if it's the 3 pin system, it just has a .01mfd cap between pins 1 and 2, and a second cap between pins 1 and 3. Since the ClearCom works on a 24 volt supply, any voltage better than 100 should be find. Local guitar repair shop would have the caps. What this does is suppress any RF content in the lines. If you have a long run, you may need one at either end if the station is local. You'll know you overdid it if they start sounding muffled. Up to that point, the more the merrier!
If a filter box has no effect, then there is an issue with the headset belt packs.

 

[Jay Ashworth]

Wandering over from the broadcast side of the house, let me ask if the radio station is actually an AM, with FM translators to fill holes?

AM is much more likely to cause this sort of hassle than FM is; if you have an AM 200 yards from you, especially if the power is sizable...

What's the station callsign?

 

[FMEng]

Trying to filter the RF with bypass capacitors won't work in this situation because the shield and pin 1 are not RF grounds at 100 MHz. There is a lot of RF current traveling on the cable shields. All of the com and power cables are acting as antennas and directing the RF right into the units. While RF can sneak in through the cases alone, it isn't nearly as much as is picked up by the long cables. Toroids can be very effective, but only when the correct material for the frequency is used, and they have to be applied in the right places. Use type 43 material for the FM broadcast band. Using a core big enough for the whole cable to pass through is highly effective because it filters the RF carried by both the signal conductors and the shield.

http://www.amidoncorp.com/43-material-round-cable-clamp-ons/

I would choose something like the 2X44-4181P2 for the com and power cables.. Choose the inner diameter needed to get a full turn (two passes) of cable, or more, through it. The more wraps through, the better. The higher the impedance (Ohms) at 100 MHz, the more effective it'll be, but the trade off is size and weight. I would pick a smaller, lighter size toroid for the headset cable, making the assumption that the relatively short cable isn't as hot. Less weight will reduce cable strain.

Apply a toroid to each and every cable where it plugs into an active device, such as a beltpack or base station. The toroid should be within a few inches of the connector. Do it for AC power cables and DC power cables, again close to the equipment. Try applying the toroids completely to a small system first. If it works, then experiment by taking toroids away, and you'll find which ones are needed. Then, add in more of the system using the proven formula. Take this approach, and I'm sure you'll be able to eliminate or substantially reduce the problem.

If it were an AM station, the same principals apply, but I would use type J material.

 

[Paul V123]

Trying to filter the RF with bypass capacitors won't work in this situation because the shield and pin 1 are not RF grounds at 100 MHz. There is a lot of RF current traveling on the cable shields. All of the com and power cables are acting as antennas and directing the RF right into the units. While RF can sneak in through the cases alone, it isn't nearly as much as is picked up by the long cables. Toroids can be very effective, but only when the correct material for the frequency is used, and they have to be applied in the right places. Use type 43 material for the FM broadcast band. Using a core big enough for the whole cable to pass through is highly effective because it filters the RF carried by both the signal conductors and the shield.

http://www.amidoncorp.com/43-material-round-cable-clamp-ons/

I would choose something like the 2X44-4181P2 for the com and power cables.. Choose the inner diameter needed to get a full turn (two passes) of cable, or more, through it. The more wraps through, the better. The higher the impedance (Ohms) at 100 MHz, the more effective it'll be, but the trade off is size and weight. I would pick a smaller, lighter size toroid for the headset cable, making the assumption that the relatively short cable isn't as hot. Less weight will reduce cable strain.

Apply a toroid to each and every cable where it plugs into an active device, such as a beltpack or base station. The toroid should be within a few inches of the connector. Do it for AC power cables and DC power cables, again close to the equipment. Try applying the toroids completely to a small system first. If it works, then experiment by taking toroids away, and you'll find which ones are needed. Then, add in more of the system using the proven formula. Take this approach, and I'm sure you'll be able to eliminate or substantially reduce the problem.

If it were an AM station, the same principals apply, but I would use type J material.

I will try this. Thank you very much.

 

[ZackeryBen]

I will try this. Thank you very much.

Did this help? I'm having the same problem.

 

[Paul V123]

I have had this happen and found a bad solder joint(in a conduit box), I was lucky i only had two legs in the system so it was easy to zero in on the fault.

What Main station are you using ? Can you separate the different runs (in the wall)?

As you can see from the original email. I have removed the main station from the rack so no wall wired connections are used. Also, I have tried 3 different main stations and one of the 3 was new out of the box. Thank you.

 

[Paul V123]

These situations can be difficult, but not impossible to fix. I am pretty sure this can be resolved, or at least reduced, with toroids, but the station engineer may not have used the right type, or didn't put them in the correct places. I will elaborate more when it isn't so late.

If you have time to elaborate. Any help would be appreciated. Thank you again.

 

[Paul V123]

Air-gap somewhere or the radio tower has faulty shunts. Typically AM is a bigger issue.
I'm assuming the radio is present no matter which physical headset you are using, a Bad solder on the ground or Shield can cause this issue.
Here's one more test to try. when you have the headset on and can hear the FM signal, turn the volume up and down. does it get louder and softer or does it stay more constant. This will help isolate whether your issue is in the base end or in the pack end. Did messing with the "Side tone" trim do anything to alleviate the issue?

The volume seems to stay constant.

 

[Paul V123]

Wandering over from the broadcast side of the house, let me ask if the radio station is actually an AM, with FM translators to fill holes?

AM is much more likely to cause this sort of hassle than FM is; if you have an AM 200 yards from you, especially if the power is sizable...

What's the station callsign?

It is FM. We can find the station on FM radio and the engineer of the station says it is FM. WBFJ.

 

[themuzicman]

Is it in one Clearcom drop or at every drop in the system? If it's at every drop, have you nulled your system properly? If it's at one drop only have you messed with the sidetone settings to see if it gets better/worse?

 

[FMEng]

If you have time to elaborate. Any help would be appreciated. Thank you again.

I did in post #9. Did you try the split toroids, of the correct type, as I explained? I've been an engineer constructing and operating high power FM stations for about 30 years, so I know a little something about RFI prevention.

 

[RonaldBeal]

Where is the stations transmitter/tower?
Where is the studio?

Could be a fault in their studio trasmitter link (STL) (Their license shows STL at 951.5Mhz)

Also. it looks like WBFJ also simulcasts on 1550 AM as well as FM... that is much more likely to be the culprit.

RB

 

[FMEng]

Interference from an STL link is extremely unlikely. The power level is too low and the beam is highly directional. It'll be easy to tell if the AM is the culprit. WBFJ AM is a daytimer, meaning they have to go off the air near local sunset. If the interference persists at night, it isn't the AM or they aren't going off as required.

Coordinates show the WBFJ FM to be 2500 Watts on top of a 96 m tall office building with a GMAC Insurance sign on it, W 5th and Poplar NW. They also have an FM translator in Sedalia. It's only 10 Watts, so if it is causing trouble, then the Clearcom is in bad shape.

 

[hithere2]

I had a similar problem our station was being picked up in the telephone system of a business across town.
after a power outage both our main and backup had come online and were transmitting together turning off the backup fixed all the problems
if it is just the one station and it is a new problem something like this might be the problem