Tech Forum

What is the preferred method of getting the frequency changed for the ALS system in my Stake Center? Our new AV distribution system was installed last year and was tested during daylight hours, and everything seemed to be fine. About a month ago was the first time that we wanted to use the ALS, and discovered that the light fixtures in the chapel cause some ugly interference, making the system unusable.

I see that in a misguided (IMHO) desire for complete centralized control, I cannot make the necessary adjustments myself (O, how I miss the good old days). Any assistance would be greatly appreciated.

Do you know what kind of system this is? For many years, the church system used RF in the 72MHz band, using companies like Comtek and Listen Technologies.

But I'm puzzled why this should start after a new system was installed unless they botched the antenna install or switched to Infrared Light (like they use in the temple).

There's no guarante that changing the frequency will fix the problem. You'd not only have to change the transmitter, but all the receivers. And it would create a problem for visitors using single-channel receivers that are tuned to the standard "church" frequency. Including visitors from other wards who still need to connect to the system in their building.

If this is an RF system, and the antenna is correctly setup, the answer would be for FM to change the fixtures. (I'll spare you the FCC Part 15 rabbit hole. Simply put, the assistive listening system are a legal user of the airwaves, the light fixtures are not.)

If they've switched to IR, then either they need to switch back to RF or change the fixtures.

It's possible that facilities installed a 216 MHz or IR ALS transmitter but didn't think to supply new receivers, or the wrong transmitter was installed. It there is no FM carrier on the receive frequency then interference or static from lights would be possible. It would go away when the transmitter is activated if the transmitter is on the same frequency as the receivers. Can the operating frequency of the transmitter be ascertained from a label on it or if not, does anyone have a receiver of some type which would cover both 72 and 216 MHz to see where it is transmitting?

The system is the Listen Technologies, and I'm pretty sure it is operating on the 72 MHz band. Previously we had a Comtek system in the same frequency band, but with a different antenna location. We haven't had any demand from members for quite awhile until just recently, so I suspect that this has been a problem for quite awhile but has just gone undetected.

Years ago we had a Spanish group meeting in the building, and for language interpretation we used a portable transmitter (made by Williams?) in the same 72 MHz frequency band. It never worked well in our building, but was at least usable. I used it once in a different building and everything was crystal clear.

This is a rural area of Idaho, so I don't see the issue of migrant receivers being a problem if the frequency is changed. We have plenty available for any visitors we may have. But if, as has been suggested, the frequency change doesn't solve the problem, we may have to push for replacement of the offending light fixtures. My stake president is an electrician, and he has been wanting the lighting changed for some time. Maybe this will be the push that will get the job done.

sjkrsmith wrote: ↑Thu Feb 09, 2023 6:05 am Previously we had a Comtek system in the same frequency band, but with a different antenna location.

If that's further away, that could be contributing to the problem. I just found out that the antenna should be mounted vertically, but the one in my stake center is horizontal. (Hmmm)

sjkrsmith wrote: ↑Thu Feb 09, 2023 6:05 am This is a rural area of Idaho, so I don't see the issue of migrant receivers being a problem if the frequency is changed.

But the members who need it will also be visiting the stake center. If they don't have a receiver that the user can tune, they'll be out of luck.

The noise from the light fixtures is probably from a switching power supply running around 10-15KHz. That means the garbage it produces will appear spaced at that same frequency. The bandwidth of a wide-band FM signal is around 75 KHz meaning that signal will appear multiple times within a channel regardless where that channel is. That's why I'm skeptical that changing the channel will do much.

Both the assistive listening system and the light fixtures fall under FM's responsibility. I'd suggest working with your stake president and dumping the problem on them.