Listen LR-100 Series, User Manual

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16
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Speci
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Programming
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 the LR-100, press the SEEK
button 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:
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 on a Listen
receiver. Using the frequency compatibility tables on pages 19-20, 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.
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 13-14) 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:
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.
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.
Channel Selection