Telex RadioCom Interference

It has be known for a while that intercom system at workplace has had interference issues, but I discovered last night that the interference is predictably occurring every 15 minutes. We're using two Telex BTR-300 base stations with at least four TR-300 beltpacks, and the interference is static with well-defined various beeps which comes in louder than people speaking, and using my cell phone with a headset on hasn't caused anything. I at least know that the system works between 150 mhz and 216 mhz from the data sheet, but I couldn't check which frequencies we use just by looking a beltpack or getting a key for rack with base stations. Now according to this site, which I can't verify accuracy, there are some county services between 150 and 160 mhz, with our building next to the county operations facility, likely hosting some high-powered transceivers. My questions regarding this is how do I check what frequency our system uses and if there is a better site besides the cumbersome FCC site to check if we overlap with someone else, and if we do overlap, how does one go about changing frequencies for our system.

Exactly every 900.00 seconds? Or just approximately every 15 minutes?

It's likely a control signal if it is in fact at exact intervals.

cpf said:

Exactly every 900.00 seconds? Or just approximately every 15 minutes?

Click to expand...

Probably not exact, I just glanced at the booth clock and knew it was coming soon every 15 minutes. Next weekend I'll be in again to make some more observations.

Can you get us a recording of the interference? The frequency of operation is determined by a crystal. There should be a sticker on the back of the base unit that gives the frequency. To change it, you would need to send the system into Telex. Chances are the county has a radio technician that might be willing to off you some assistance in determining what is happening.

FMEng, I be in next weekend and I can record it and see if I can get into the rack and check the frequency our system uses. I'll send mail to someone in the county with frequency and ask if they use it. But if this involves a significant amount of money to send our base stations out, it probably won't get fixed. Should Telex, the distributor, or installer have checked for frequency conflicts like with checking a wireless mic system isn't overlapping with TV stations, especially when it isn't user-configurable?

If this is a new issue that cropped up after the install, it would be hard to blame anyone (assuming the frequency range is licensed for general use). If the installer checked the frequency, they would have found it clear. Then at a later date, whoever installed what's causing the interference would probably have done the same check, but unless you were using your system at the time, they would have found nothing too.

frequency groups for the BTR/TR300 Radiocom System

the last 5 digits in the model # (Catalog Number: 7127-XXXXX) should jibe with something on this chart for you to determine freq. The front panel of the BTR300 has an receive enable button for each TR belt pack. disable all packs at the base station and see if you still have the problem. hopefully the problem is not still there. if not then enable one pack at a time to figure the problem freq.

btw: the ID/freq info on my BTR300 basestation is on the bottom. so if you are going to look at the base station you will likely need to remove it from the rack to view the information.

Update: I was back on Sunday and we were using two headsets and had both base stations on. The 15 minute recurring interference was gone, and it didn't occur early in the week too. I'll be back here if it happens again.

I'm late to the party on this but it seems to me that the interference may in fact be a 2-way radio transmitter that is broadcasting a station ID on a 15 minute timer. This is fairly common on older VHF systems that are not used all the time and keeps the station "active" according to FCC requirements.