6-2 TROUBLESHOOTING MDS 05-2415A01, Rev. A
2. Transmitter Power Measurement
a. Measure transmitter power output at the ANTENNA connector with an in-line
wattmeter or a service monitor. It should not exceed 5 watts.
3. Transmit Modulation Evaluation
a. Check to see that transmit audio connections are properly made.
b. Check transmitter deviation and adjust, if necessary.
4. Transmit Frequency Measurement
a. Check transmit carrier frequency with a service monitor or frequency counter
(± 0.000015% accuracy).
UNIT TRANSMITS, BUT DOES NOT RECEIVE
1. Receive Audio Evaluation
a. Check for receive audio on Pin 11 of the DB-25
INTERFACE connector.
b. Check for proper receive frequency programming using HHT or PC terminal.
c. Check that RUS line (Pin 10 of DB-25) goes high with a received signal.
2. Interface Functions—With Diagnostics Board Installed
a. Check power supply voltage (
SV).
b. Check 8 volt regulator (
VR).
c. Check PLL VCO lock voltage (
LV).
d. Check RSSI voltage (
RSSI).
e. Check power output (
KEY & FPWR).
f. Check programmed transmit and receive frequencies (
FRQ).
UNIT RECEIVES AND TRANSMITS, BUT SYSTEM PERFORMANCE IS POOR
1. Transmitter Evaluation
a. Check transmit carrier frequency with a service monitor or frequency counter
(± 0.000015% accuracy).
b. Check transmitter modulation (≈2.5 kHz).
c. Check RF output power level. It should not exceed 5 watts.
2. Receiver Evaluation
a. Check receive 12 dB SINAD sensitivity at Pin 11 of DB-25 connector
(–117 dBm/0.3 µV).
b. Check audio output level.
c. Check squelch threshold level. Squelch should open at a level greater than
–120 dBm
d. Check Master Station received signal strength using the HHT and the
RSSI
command, or measure the DC voltage at Pin 21 of the INTERFACE connector.
(See Figure 2-4 to interpret the DC signal level in dBm.)
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