4-10 FIELD TESTS & ADJUSTMENTS MDS 05-2415A01, Rev. A
TEST PROCEDURE ➋:
TRANSMIT FREQUENCY, SQUELCH, DEVIATION,
AND RECEIVE AUDIO OUTPUT—For Radios with No Internal Modem
Remove the cover from the transceiver by loosening the four captive cover screws and lifting
it straight up. See Figure 4-9 for the locations of adjustable controls.
Transmit Frequency
1. Connect the transceiver’s ANTENNA connector to the input of the service monitor
using a short length of RG-8/U or RG-214 coaxial cable.
2. Key the transmitter by entering KEY on the HHT or use the Transmit Test Switch.
The KEY command keys the transmitter until the DKEY command is entered or until
the time-out period has passed.
3. Measure the transmitter frequency. It should be within 100 Hz of the assigned
frequency. If not, adjust the transmitter frequency on the TCXO.
R
M
If Remote Maintenance is installed, use the IF / DF / INCF / DECF commands
instead of adjusting the Frequency Adjust on the TCXO. The IF / DF
commands increment/decrement the frequency in single steps while the
INCF / DECF commands make larger jumps by adding a space and a number
to the command. (For example: INCF_8 to increase the frequency by eight
steps out of 100.) When finished, type RMST to store the setting.
4. Unkey the transmitter and reconnect the interface cable to the external modem or
RTU.
Receive Audio Output Level
The receive audio output level of the transceiver is factory-set for 0.7 Vp-p (–10 dBm) at
600 Ω, at rated system deviation. If a third party modem is used with the MDS 4310, consult
its instruction manual to determine what audio input level the modem needs. Should a
different level be required, adjust the Receive Audio Output Level, R292, on the transceiver
board as follows:
1. Generate an on-channel signal modulated with a 1 kHz tone, at the proper deviation
level (commonly 2.5 kHz), to provide an audio signal for adjustment purposes.
Monitor the level at the input to the modem (or at Pin 11 of the
INTERFACE
connector) using the oscilloscope in the service monitor. Adjust R25 on the main
transceiver board for the desired level.
An alternate method is to adjust R25 when data signals from the master station are
present and audio tones can be seen on the scope.
2. Reconnect the feedline directly to the ANTENNA connector of the transceiver. Place
the unit in normal operation with the associated master station.
Squelch Adjustment
1. Consult the RTU instruction manual to determine if squelch action in the radio is
required for normal operation. If squelch action is not required, set Squelch
Threshold, R41, fully counterclockwise (open squelch) and skip the remaining steps
of this procedure. If you are unsure on this point, assume that squelch action is
required and perform the following procedures.
2. Remove the feedline from the ANTENNA connector.
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