Listen Technologies LR-300 EN - Manual (Page 48)

44
Information
Channel Selection
It is highly recommended that after channel selection has been achieved, you lock the channel so that
it cannot be changed by the user. To accomplish lock on receivers, press and hold seek for 5 seconds.
Repeat the process to unlock. It is important to choose channels that are free from interference to
achieve proper operation of your Listen equipment. This process is trial and error. Before turning on the
transmitter, listen to the wide band channels (lettered channels at 72 MHz and channels that start with a
“2” for 216 MHz). Listen to the audio through the headphone or via the speaker. Choose a channel with
the least amount of interface. Unless you are interfacing with an existing narrowband transmission
system, always use a wide band channel. If you are using multiple channels follow this process:
a. Same Space If you are using transmitters in the same space, the most number of channels that will
work simultaneously is six at 72 MHz and three at 216 MHz. With all of the transmitters off, listen for
interference on all the wide band channels via the headphone jack. Using the frequency
compatibility tables on pages 47-48, eliminate any channels that have noticeable interference. Now
choose the channels with the widest channel spacing. It is recommended that adjacent channels be
spaced at least 300 KHz. If there is no interference the following channels are recommended: A, C, E,
I, J, and H for 72 MHz and channels 2A, 2K and 2V at 216 MHz.
b. Distributed Spacing If you are using transmitters that are spread out over space, you can achieve
more simultaneous broadcast channels. However, it is critical that your receiver(s) be located as
close to its transmitter as possible. You can use adjacent channels (see frequency compatibility
tables on pages 47-48) in this case as long as the adjacent channel transmitter is at least 50% further
away from the receiver as its transmitter. Example: The transmitter for the receiver on channel E is 100
feet from the receiver. The adjacent channel transmitter on channel D should be at least 150 feet
away.
Notes in regard to using 72 MHz and 216 MHz systems:
i. 72 MHz in a secondary frequency band. This means that other transmitters are licensed to use these
frequencies. Thus, you may experience interference from paging transmitters and other type
transmissions. You will need to find a clear channel by listening to all the wide band channels.
ii. 216 MHz is a primary frequency band and no other types of transmissions are authorized to use it.
Thus, you will find the highest probability of clear channels in this band. However, you may
experience intermodulation of the TV Channel 13 aural carrier if there is a channel 13 transmitter in
your area and you are close to the transmitter. If you cannot find a clear channel in 216 MHz band
due to channel 13, it is recommended that you switch to a 72 MHz system.
NOTE: The LR-300-072 can only be used with the 17 wide band 72 MHz channels, if you are using the
LR-300 choose only lettered wide band frequencies on your transmitter.