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
