Appendix A
Which channel(s) should I use?
NOTE: 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, press and hold the SEEK button for five seconds on the LR-100 and portable
receivers. On the LT-700, press either the UP or DOWN button for 5 seconds, and on the LT-800, press both the UP and DOWN
buttons simultaneously 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 72MHz and channels that start with a “2” for 216MHz). 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 72MHz and three at 216MHz. With all of the transmitters off, listen for interference on all the wide band channels
via the headphone jack. Using the channel selection guide on pages 39-42, 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 300KHz. If there is no interference the following channels are recommended: A, C, E, I, J, and H for 72MHz
and channels 2A, 2K and 2V at 216MHz.
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 selection charts on page 37-40) 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 72MHz and 216MHz systems:
i. 72MHz 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. 216MHz 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 216MHz band due to channel 13, it is recommended that you switch to a 72MHz system.
Appendix A
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