Hearing Impaired Tramsitter Antenna Location

We recently upgraded our transmitter and are getting a lot of static with the Assisted Listening system. We would like to upgrade the antenna also but have not been able to find its location anywhere in the building. Our FM group is looking for the building plans. Does anyone know where the antenna is traditionally located in the chapel?

dhunsaker6 wrote: Fri Sep 29, 2023 8:36 pm Does anyone know where the antenna is traditionally located in the chapel?

Usually the transmitter is in the sound rack, and the antenna has something like 25-50' of cable or so. Find the transmitter and follow the wire. In the case of my stake center, it's in an area above the sound rack where the organ speakers are.

It does beg the question why things got worse after the transmitter was changed. Probably a bad connection somewhere or they accidently pulled the antenna down trying to connect it.

It varies from building to building and installer on where the antenna might be located. How old is your building? Where is the sound cabinet located?

Listen Tech 50 ohm impedance.
Comtech and Williams are 75 ohm impedance.

Feed line and antenna should be changed out as part of transmitter swap if going to Listen TX.

These are very low power systems and you need to preserve as much gain and efficiency in your system as possible.

Also our antenna is mounted to wall in center of the furnace room over the overflow.

Dave- that would sound like a late 60s thru 1970s stevens design building with the mech room above the overflow. I have worked in a few of those buildings, found 1 or 2 that had the sound cabinet up there as well, and a few that at one time had the sound cabinet up there but the cabinet was later relocated down to the main floor in a room.

Replace the Listen Technologies LT-800 transmitter (very low power output) with a Comtek BST-75 transmitter (much higher power output). That will solve your problem.

I have measured the RF output power of my LT-800-072 and here are the power levels measured.

High 0.0275 watts
Med. 0.00437 watts
Low. 0.00103 watts

The published spec for the Comtek BST-75 is 0.120 watts

These transmitters all very low power systems designed for in building use. This is a roughly 6 dB gain advantage.

Hey Dave.

You may be measuring an older Listen unit, as anything manufactured after 2016 will have a max output of about 2 dBm (less than 2 mW). I've recently measured several Listen units in various buildings, they all come in right around 2 dBm at max power.

By contrast the current Comtek BST-75 offering has an output power just shy of 21 dBm (120 mW). I've also measured several of these recently and confirmed this to be accurate. Thus the output delta between these two units is 18+ dB, which is huge from an RF coverage/quality perspective. The Comtek transmitters will cover much more than the Listen units in the same installation.

dave.swartz wrote: Wed Oct 04, 2023 1:47 pm Listen Tech 50 ohm impedance.
Comtech and Williams are 75 ohm impedance.

Not sure which models you are referring to, but for these assisted listing systems:
Listen LT-800 FM Transmitter antenna output is 50 Ohm
Comtek BST-75 Transmitter is also 50 Ohm RF output

The Williams Sound PPA T27 portable transmitter (used for interpretation) is 75 Ohm RF output.

All three systems use channels in the same FM frequency ranges (channels are select-able) so depending on transmitter and receiver settings, interpretation receivers can pick up assisted listening transmissions and assisted listening receivers can pick up interpretation transmissions. Normally the systems are set to different channels during installation.