User Manual
MT-4E VHF & UHF Receiver & Transmitter Instruction Manual
IM08-MT-4E-TXRX Project 1106
Hardware Tuning and Troubleshooting
18
Synthesizer and UDB Modules
The Synthesizer module and UDB are bound together through their communication link. At this level
of fault diagnosis it is not feasible to isolate the problem between two units.
If the receiver front panel ON/OFF switch is set from the OFF position to the NORM position and the two
front panel LEDs stay on, check that the Synthesizer and the UDB are properly seated on the Receiver
Main Board and check the following test points on the UDB (to access the UDB, the shield lid covering
the UDB will need to be removed as shown on the MT-4E Receiver Bottom Component View):
Test Point Signal Monitored Typical voltage
TP2 Logic power +3.3 VDC ± 5 %
TP3 DSP core supply +1.2 VDC ± 5 %
TP4 CPLD core supply +1.8 VDC ± 5 %
Test Points are shown on the MT-4E Receiver Jumper and Test Point Locator Illustrations.
If the UDB voltages are not within the specied tolerances, it is most likely that the Receiver Main
Board (that supplies these voltages to the UDB) is faulty or there is a short within the UDB.
If the UDB voltages are within the specied tolerances, inject a -70 dBm carrier on the Receiver
frequency into the RF Input and check the RSSI Meter reading in the Service section of the RSS. If
the RSSI Meter reading is low (< 30), perform the following test to verify that the synthesizer is locked
on frequency:
Disconnect the LO output SMB connector from the Synthesizer to the RF Preselector, as shown on
the MT-4E Receiver Top Component View (1), and connect the Synthesizer LO output to a radio
communication test set. Conrm that the synthesizer LO frequency matches the Target Synthesizer
RF OUT found in the Reference Oscillator area of the Service section on the RSS. The LO output
should be approximately +7 dBm.
Check that the LO output (21.4 MHz above or below the receiver frequency / 73.35 MHz @ 800 MHz)
of the synthesizer module is within the receiver frequency tolerances of ± 1.0 ppm (VHF) / ± 0.5 ppm
(UHF) and ± 0.1 ppm @ 800 mHz, and that the RF frequency will change with programmed channel
changes in the RSS. If this is not the case, it is most likely that the synthesizer or the UDB or both are
faulty. The fault may be associated with the synthesizer code, the DSP Code or both.
Receiver RF Preselector
Check the +9.5 VDC Power Supply wire to the RF Preselector as shown on the MT-4E Receiver Top
Component View (2). The supply voltage should be +9.5 VDC ± 5 %. inject a -30 dBm carrier on the
Receiver frequency into the RF Input and check the IF Output of the RF Preselector is 21.4 MHz and
73.35 MHz @ 800 MHz, and it can be demodulated through the communication test set. If this is not
the case the synthesizer, the RF Preselector or both are faulty.
To further isolate the fault, the LO output as shown on the MT-4E Receiver Top Component View (1)
can be disconnected from the Synthesizer, and an LO input can be applied from an external source to
the RF Preselector. The frequency of the external LO input should be the Target Synthesizer RF OUT
found in the Reference Oscillator area of the Service section on the RSS. Check the 21.4 MHz and
73.35 MHz @ 800 MHz output of the module using a communication test set.