Maxon Telecom SM-2000 service manual SM-2450/UHF Alignment Procedure, PLL Alignment

Page 31

MAXON SM-2000 MOBILE

SM-2450/UHF ALIGNMENT PROCEDURE

SM-2450/UHF ALIGNMENT PROCEDURE

It is important that the TCXO be on the correct frequency before performing a complete alignment of the radio. An incorrect TCXO frequency can impair the performance and even cause mis-alignments.

Normally the transmitter is monitored with a frequency counter or service monitor while the transmitter is keyed at its highest frequency. The TCXO is adjusted for the least frequency error. Typically the frequency is 470MHz with a frequency error of +/- 750Hz or less. TC701 adjusts the center frequency if necessary.

PLL Alignment

NOTE: If the PLL is out- of- lock, an audible warning will be heard and the front panel red LED will flash.

1.Connect an RF power meter to the ANT jack.

2.Using the channel switch, select the channel with the highest transmit frequency.

3.Connect a DC voltmeter to test point 1 ( TP1 ), accessed via the hole in the VCO cover.

4.Set the PTT switch to transmit.

5.Adjusting TC101 , set the voltage measured at TP1 to 12.0 (+/- 0.05) volts.

6.Release the PTT switch.

7.Using the channel switch, select the channel with the lowest receive frequency.

8.At TP1 measure and check that the voltage is 1.4 volts or more. If the voltage is below 1.4 volts the VCO may not lock because the lowest RX frequency is programmed too far below the TX frequency.

Receiver Alignment RF

NOTE: The Receiver front end is a pre-aligned module. There are no available field adjustments.

1.Connect an RF signal generator to the ANT socket and a SINAD meter to the external speaker jack ( J1 ) located at the rear panel.

2.Adjust RV103 to the fully open position to hear receiver noise.

3.Adjust the VOLUME control to mid position.

4.Using the channel switch, select the programmed middle receive frequency.

5.Set the RF signal generator to the same receive channel frequency.

6.Set the audio frequency to 1kHz at 3K deviation for wide band (25kHz).

6B. Set the audio frequency to 1kHz at 1.5K deviation for narrow band (12.5kHz).

7.Adjust the RF output voltage level of the RF signal generator until the 1kHz signal is heard.

NOTE: The RF output voltage level and the SINAD reading.

8.Adjust T102 for an improvement in SINAD.

9.Adjust the RF output voltage level of the RF signal generator keeping the SINAD meter readings between 6dB and 12dB .

10.Adjust T101 for an improvement in SINAD.

Page-27-

December 98

Image 31
Contents SM-2000 Page Maxon SM-2000 Mobile Table of ContentsPCB Layouts Schematics and Block DiagramsSM-2000 Exploded View Transceiver Nominal Performance SpecificationsGeneral Band Operational BandwidthTransmitter Specfications SUB Audible Tones DCS TX Tone Modulation CharacteristicsReceiver Reliability Analysis RX Tone Demodulation CharacteristicsAccessories Subaudible tones CTCSS/DCSIntroduction Check the carton carefully for the following items Unpacking InformationGeneral Description Description of Controls Description of ControlsSM-2000 Rear Panel CTCSS/DCS Encoder Circuit Theory of OperationDigital Circuitry CTCSS/DCS Decode CircuitsEeprom PLL RF Section SM-2150/VHF TX VCO RX VCORF Amplifier Out of Lock DetectorPrescaler ReceiverNoise Detect Circuit SQ Board Receiver Audio CircuitLow Pass Filter Audio AmplifierUHF Transmitter RF Section SM-2450/UHFFrequency Synthesizer Circuit First Mixer Voltage Controlled Oscillator CircuitSecond Oscillator- Mixer- Limiter and FM Detector Speaker Audio Amplifier Squelch Mute CircuitSquelch Noise Band Pass Filter Noise DetectorTransmit Tests Test SetupPLL Alignment SM-2150/VHF Alignment ProcedureReceiver Alignment RF Discriminator TuningAutomatic Power Adjustment Squelch AdjustmentModulation Deviation Adjustment CTCSS/DCS Deviation AdjustmentAlignment Points Diagram SM-2150/VHF SM-2450/UHF Alignment Procedure Page-28 December ∙ Note Release the PTT button when changing channels Page-30 December Alignment Points Diagram SM-2450/UHF Surface Mount Components Component ReplacementSurface Mount Removal Surface Mounted Integrated Circuit Replacement Surface Mount Component ReplacementREF # Description Parts List Common to SM-2000Digital Parts Common on Both VHF & UHF Digital Section REF # Description FRONT-END PCB Assembly Main Board Parts Band ChartPage-38 December Page-39 December Page-40 December Page-41 December SM-2450A UHF Band SM-2450C UHF Band SM-2450D UHF Band SM-2450E UHF Band Band ChartPage-44 December Page-45 December Page-46 December Page-47 December Component Pinout Page-49 December Page-50 December IC409 Voltage Charts SM-2150/VHFPage-52 December Transistor Voltage Chart Voltage Charts SM-2450/UHF IC404 Page-56 December Status Indications & Audible Tones Trouble Shooting Chart SM-2000Page-58 December MMBV109 Replacement Module SchematicsMA-4472 Microphone Schematic Page-61- December Page-62- December Page-63- December Page-64- December SM-2000 Control Head SW5Page-66 December SM-2150/VHF Main Board AssyFront SM-2450/UHF Main Board AssySM-2000 SM-2150/VHF Exploded View Parts List Intentionally Left Blank