Channel Selection - Listen LT-700-072 User Manual

Channel Selection

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 when
using a Listen receiver). Listen to the audio through the headphone or on a Listen receiver or
receiver / 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 multiple 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 on a
Listen receiver. Using the frequency compatibility tables on pages 17-18, 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 frequency compatibility
tables on pages 17-18) 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.
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 LT-700, press both the UP and DOWN
buttons simultaneously for 5 seconds. Repeat the process to unlock.
Notes in regard to using 72MHz and 216MHz systems:
i. 72MHz is 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 types of
transmissions. You will need to fi nd 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 fi nd 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 fi nd a clear channel in 216MHz band due to
channel 13, it is recommended that you switch to a 72MHz system.
14
Wide Band Recommendation
Listen recommends that you always use
a wide band channel unless you need to
be compatible with existing narrow band
receivers from other manufacturers. Wide
band channels have lower noise than their
narrow band counterparts.
At 72MHz
The LT-800 at 72MHz operates on 17
wide band channels and 40 narrow band
channels.
• Letters= Wide Band Channels
(Example: E)
• Numbers= Narrow Band
Channels (Example: 32)
At 216MHz
The LT-800 at 216MHz operates on 19
wide band channels and 38 narrow band
channels.
• "2" as left digit= Wide Band Channel
(Example: 2C)
• "1" and ì3î as left digits= Narrow Band
Channels
(Examples: 1A; 3R)