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RTU-292 Operations Manual
2.10.1.2
Adjust TX Level Adjust so that the transmitter is just fully modulated. If the transmitter is AM
or SSB, use its output power meter (if available) to determine the amount of modulation. Do
this by advancing R133 clockwise just until the power meter stops rising. This will produce
maximum modulation without activating the radio’s compressor. When using an FM
transmitter, a deviation meter may be necessary to determine the amount of modulation.
NOTE
The RF Power meters on most SSB transmitters do not respond accurately to voice
peaks, so a low RF meter indication on actual voice from the RTU-292 may make
the transmitter appear
to be under modulated. If the TX Level Adjust is increased
in an attempt to compensate for a low meter indication, level compression will
likely result, which will degrade system performance. If there is any doubt about
the amount of modulation being obtained, monitor the RF output with an
oscilloscope to observe the true conditions.
NOTE
Avoid excessive level into the transmitter. While most modern transmitters have
modulation limiters which will not allow them to over-modulate, excessive level
into the transmitter will cause level compression of the signal which effectively
degrades the hybrid null provided by the RTU-292. This is particularly important
with a full duplex system, which may oscillate if too much level compression is
used. For best results, adjust the TX Level Adjust so that the transmitter is just
fully modulated by the test tone or actual phone line audio.
NOTE
If the Transmit Level Set-up Mode was used, be sure to take the unit out of this
mode after set-up is complete by turning off the main power, switching SW2-7
back to OFF, and turning the power back on.
2.10.2 SETTING THE RECEIVE LEVEL
The audio level into the RTU-292 from the radio receiver is set by the internal RX Level
adjustment potentiometer, R116. The PEAK LED responds to the receiver audio coming from
the radio and is provided as a guide to setting this level (there are two peak LEDs, CR24 on the
Main Board as well as the front panel PEAK LED). The TEL LINE/RADIO button must be
ON for the PEAK LED to function. The level is correctly set when the PEAK LED flashes
occasionally (once per second to once every few seconds) in response to voice peaks in the
incoming audio. If the indicator flashes continuously, the level is too high and must be
reduced.
To set the level, tune the receiver to a station with a strong signal that will provide maximum
audio into the RTU-292. Turn the RX Level Adjust control clockwise (to increase the level) or
counterclockwise (to decrease the level) as necessary until the PEAK indicator flashes
JPS Communications, Inc.
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