Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual
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GM338 Mobile Radios UHF1 40W Bipolar (403-470MHz) Service Information Issue: December, 2003
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i Table of Contents Section 1 Model Chart and Technical Specifications 1.0 GM338 Model Chart............................................................................................. 1-1 2.0 Technical Specifications ...................................................................................... 1-1 Section 2 Theory of Operation 1.0 Introduction .......................................................................................................... 2-1 2.0 UHF (403-470 MHz) Receiver ............................................................................. 2-1 2.1 Receiver Front-End ........................................................................................ 2-1 2.2 Front-End Band-Pass Filters & Pre-Amplifier ................................................. 2-2 2.3 First Mixer and 1st Intermediate Frequency (IF) ............................................ 2-2 2.4 2nd Intermediate Frequency (IF) and Receiver Back End ............................. 2-3 3.0 Transmitter Power Amplifier (PA) 40 W ............................................................... 2-3 3.1 Power Controlled Stage.................................................................................. 2-4 3.2 Pre Driver Stage ............................................................................................. 2-4 3.3 Driver Stage.................................................................................................... 2-4 3.4 Final Stage ..................................................................................................... 2-4 3.5 Bi-Directional Coupler..................................................................................... 2-5 3.6 Antenna Switch............................................................................................... 2-5 3.7 Harmonic Filter ............................................................................................... 2-5 3.8 Power Control ................................................................................................. 2-5 4.0 Frequency Synthesis ........................................................................................... 2-6 4.1 Reference Oscillator ....................................................................................... 2-6 4.2 Fractional-N Synthesizer ................................................................................ 2-7 4.3 Voltage Controlled Oscillator (VCO) ............................................................... 2-8 4.4 Synthesizer Operation .................................................................................... 2-9 Section 3 Troubleshooting Charts 1.0 Troubleshooting Flow Chart for Receiver ............................................................ 3-1 2.0 Troubleshooting Flow Chart for 40W Transmitter ................................................ 3-3 3.0 Troubleshooting Flow Chart for Synthesizer ........................................................ 3-4 4.0 Troubleshooting Flow Chart for VCO ................................................................... 3-5
ii Section 4 UHF PCB/Schematics/Parts Lists 1.0 Allocation of Schematics and Circuit Boards ....................................................... 4-1 1.1 Controller Circuits ........................................................................................... 4-1 2.0 UHF 25-40W PCB / Schematics / Parts List ........................................................ 4-3 UHF (403-470 MHz) 25-40W 8480643Z06 Top Side ............................................. 4-3 UHF (403-470 MHz) 25-40W 8480643Z06 Bottom Side ....................................... 4-4 UHF (403-470 MHz) Power Amplifier 25-40W ....................................................... 4-5 UHF (403-470 MHz) FRACN .................................................................................. 4-6 UHF (403-470 MHz) Voltage Controlled Oscillator................................................. 4-7 UHF (403-470 MHz) Receiver Front End ............................................................... 4-8 UHF (403-470 MHz) IF ........................................................................................... 4-9 UHF PCB 8480643Z06 Parts List 25-40W ........................................................... 4-10
1-1 Section 1 MODEL CHART AND TECHNICAL SPECIFICATIONS 1.0 GM338 Model Chart 2.0 Technical Specifications Data is specified for +25°C unless otherwise stated. GM Series, UHF Band 1, 403-470 MHz Model Description AZM25RKF9AA5GM338 403-470 MHz 25-40W Conv Pref (Bipolar) Item Description XGCN6114_GM338 Control Head Direct Mount X IMUE6012_ Tanapa WM 403-470 MHz 25-40W XRAE4151_BNC 403-430 MHz, 1/4 Wave Roof Mount X RAE4152_ BNC 450-470 MHz, 1/4 Wave Roof Mount XRAE4153_BNC 450-470 MHz, 3.5dB Gain Roof Mount X RAE4154_ BNC 450-470 MHz, 5dB Gain Roof Mount XRAE4158_BNC 406-420 MHz, 3.5dB Gain Roof Mount X 6804112J06 GM338 User Guide x = Indicates one of each is required. General Specifications Channel Capacity GM338 128 Power Supply 13.2Vdc (10.8 - 15.6Vdc) Dimensions: H x W x D (mm) Depth excluding knobsGM338 59mm x 179mm x 198mm (25 - 40W) (add 9mm for Volume Knob) Weight GM338 1400 g Sealing:Withstands rain testing per MIL STD 810 C/D/E and IP54 Shock and Vibration: Protection provided via impact resistant housing exceeding MIL STD 810-C/D/E Dust, Salt & Fog:Protection provided via environment resistant housing exceeding MIL STD 810 C/D/E
1-2Technical Specifications *Availability subject to the laws and regulations of individual countries.Transmitter UHF *Frequencies - Full BandsplitUHF 403-470 MHz Channel Spacing12.5/20/25 kHz Frequency Stability (-30°C to +60°C, +25° Ref.)±2.0 ppm Power 25-40W Modulation Limiting±2.5 @ 12.5 kHz ±4.0 @ 20 kHz ±5.0 @ 25 kHz FM Hum & Noise-40 dB @ 12.5kHz -45 dB @ 20/25kHz Conducted/Radiated Emission (ETS)-36 dBm 1 GHz Adjacent Channel Power-60 dB @ 12.5 kHz -70 dB @ 25 kHz Audio Response (300 - 3000 Hz)+1 to -3 dB Audio Distortion @1000Hz, 60% Rated Maximum Deviation65 dB Adjacent Channel Selectivity (ETS) 65 dB @ 12.5 kHz 70 dB @ 20 kHz 75 dB @ 25 kHz Spurious Rejection (ETS)70 dB @ 12.5 kHz 75 dB @ 20/25 kHz Rated Audio 3W Internal 7.5W External 13W External Audio Distortion @ Rated Audio
2-1 Section 2 THEORY OF OPERATION 1.0 Introduction This Chapter provides a detailed theory of operation for the UHF circuits in the radio. For details of the theory of operation and troubleshooting for the the associated Controller circuits refer to the Controller Section of this manual. 2.0 UHF (403-470 MHz) Receiver 2.1 Receiver Front-End The receiver is able to cover the UHF range from 403 to 470 MHz. It consists of four major blocks: front-end bandpass filters and pre-amplifier, first mixer, 1st IF, 2nd IF and receiver back-end . Two varactor tuned bandpass filters perform antenna signal pre-selection. A cross over quad diode mixer converts the signal to the 1st IF of 44.85 MHz. Low side first injection is used. Figure 2-1 UHF Receiver Block Diagram Demodulator 1. Crystal Filter Mixer Va r a c t o r Tuned Filter RF Amp Va r a c t o r Tuned Filter Pin Diode Antenna Switch RF Jack Control Voltage from PCICFirst LO from FGU Recovered Audio RSSI Second LO 2. Crystal Filter 455kHz Filter (25kHz)455kHz Filter (25kHz) 455kHz Filter (12.5kHz)455kHz Filter (12.5kHz)SwitchSwitchSwitchSwitch Limiter 1. IF Amp 2. IF Amp Filter Bank Selection from Synthesizer IC Harmonic Filter BWSELECT
2-2UHF (403-470 MHz) Receiver The 2-pole 44.85 MHz crystal filters in the 1st IF section and two pairs of 455 kHz ceramic filters in the 2nd IF section provide the required adjacent channel selectivity. The correct pair of ceramic filters for 12.5 or 25 kHz channel spacing is selected via control line BWSELECT. The 2nd IF at 455 kHz is mixed, amplified, and demodulated in the IF IC. The processing of the demodulated audio signal is performed by an audio processing IC located in the controller section. 2.2 Front-End Band-Pass Filters & Pre-Amplifier The received signal from the radio’s antenna connector is first routed through the harmonic filter and antenna switch, which are part of the RF power amplifier circuits, before being applied to the receiver pre-selector filter (C4001, C4002, D4001 and associated components). The 2-pole pre-selector filter tuned by the varactor diodes D4001 and D4002 pre-selects the incoming signal (RXIN) from the antenna switch to reduce spurious effects to following stages. The tuning voltage (FECTRL_1) ranging from 2 volts to 8 volts is controlled by pin 20 of PCIC (U4501) in the Transmitter section. A dual hot carrier diode (D4003) limits any inband signal to 0 dBm to prevent damage to the pre- amplifier. The RF pre-amplifier is an SMD device (Q4003) with collector base feedback to stabilize gain, impedance, and intermodulation. The collector current of approximately 11-16 mA is drawn from the 9.3 volt supply via L4003 and R4002. A 3dB pad (R4006,R4007,R4011 and R4008 - R4010) stabilizes the output impedance and intermodulation performance. A second 2-pole varactor tuned bandpass filter provides additional filtering of the amplified signal. The varactor diodes D4004 and D4005 are controlled by the same signal FECTRL_1, which controls the pre-selector filter. A following 1 dB pad (R4013 - R4015) stabilizes the output impedance and intermodulation performance. 2.3 First Mixer and 1st Intermediate Frequency (IF) The signal coming from the front-end is converted to the first IF (44.85 MHz) using a cross over quad diode mixer (D4051). Its ports are matched for incoming RF signal conversion to the 44.85 MHz IF using low side injection via matching transformers T4051 and T4052. The injection signal (RXINJ) coming from the RX VCO buffer (Q4332) is filtered by the lowpass filter consisting of (L4053, L4054, C4053 - C4055) followed by a matching transformer T4052 and has a level of approximately 15dBm. The mixer IF output signal (IF) from transformer T4501pin 2 is fed to the first two pole crystal filter FL3101. The filter output in turn is matched to the following IF amplifier. The IF amplifier Q3101 is actively biased by a collector base feedback (R3101, R3106) to a current drain of approximately 5 mA drawn from the 5 volt supply. Its output impedance is matched to the second two pole crystal filter FL3102. The signal is further amplified by a preamplifier (Q3102) before going into pin 1 of IFIC (U3101). A dual hot carrier diode (D3101) limits the filter output voltage swing to reduce overdrive effects at RF input levels above -27 dBm.
Transmitter Power Amplifier (PA) 40 W2-3 2.4 2nd Intermediate Frequency (IF) and Receiver Back End The 44.85 MHz 1st IF signal from the second IF amplifier feeds the IF IC (U3101) at pin1. Within the IF IC the 44.85 MHz high IF signal mixes with the 44.395 MHz second local oscillator (2nd LO) to produce the low IF signal at 455 kHz. The 2nd LO frequency is determined by crystal Y3101. The 2nd IF signal is amplified and filtered by an external pair of 455 kHz ceramic filters (FL3112, FL3114) for 20/25 kHz channel spacing or FL3111 and FL3113/F3115 for 12.5 kHz channel spacing. These pairs are selectable via BWSELECT. The filtered output from the ceramic filters is applied to the limiter input pin of the IF IC (pin 14). The IF IC contains a quadrature detector using a ceramic phase-shift element (Y3102) to provide audio detection. Internal amplification provides an audio output level of 120 mV rms (at 60% deviation) from U3103 pin 8 (DISCAUDIO) which is fed to the ASFIC_CMP (U0221) pin 2 (part of the Controller circuits). A received signal strength indicator (RSSI) signal is available at U3101 pin 5, having a dynamic range of 70 dB. The RSSI signal is interpreted by the µP (U0101 pin 63) and is available at accessory connector J0501-15. 3.0 Transmitter Power Amplifier (PA) 40 W The radio’s 40W power amplifier (PA) is a four stage amplifier used to amplify the output from the VCOBIC to the radio transmit level. It consists of the following four stages in the line-up. The first stage is a LDMOS predriver (U4401) that is controlled by pin 4 of PCIC (U4501) via Q4473 (CNTLVLTG). It is followed by another LDMOS stage (Q4421), an LDMOS stage (Q4431), and a bipolar final stage (Q4441). Figure 2-2 UHF Transmitter Block Diagram Device Q4401 is surface mounted. Q4421, Q4431 and Q4441 are directly attached to the heat sink.PCIC Pin Diode Antenna Switch RF JackAntenna Harmonic Filter PowerSensePA - F i n a lStag ePADriver From VCOControlledStage VcontrolBias 1Bias 2 To Microprocessor Temperature Sense SPI BUS ASFIC_CMP PA PWR SET To Microprocessor
2-4Transmitter Power Amplifier (PA) 40 W 3.1 Power Controlled Stage The first stage (U4401) amplifies the RF signal from the VCO (TXINJ) and controls the output power of the PA. The output power of the transistor U4401 is controlled by a voltage control line feed from the PCIC pin4(U4501). The control voltage simultaneously varies the bias of two FET stages within U4401. This biasing point determines the overall gain of U4401 and therefore its output drive level to Q4421, which in turn controls the output power of the PA. In receive mode the voltage control line is at ground level and turns off Q4473 which in turn switches off the biasing voltage to U4401. 3.2 Pre Driver Stage The next stage is a 13dB gain LDMOS device (Q4421) which requires a positive gate bias and a quiescent current flow for proper operation. The voltage of the line PCIC_MOSBIAS_1 is set in transmit mode by PCIC pin 24 and fed to the gate of Q4421 via the resistive network R4407, R4408, R4416 and R4415. The bias voltage is tuned in the factory. 3.3 Driver Stage The following stage is an enhancement-mode N-Channel MOSFET device (Q4431) providing a gain of 10dB. This device also requires a positive gate bias and a quiescent current flow for proper operation. The voltage of the line Bias_2_UHF_PA_1 is set in transmit mode by the ASFIC and fed to the gate of Q4431 via the resistive network R4630, R4631, and R4632. This bias voltage is also tuned in the factory. If the transistor is replaced, the bias voltage must be tuned using the Customer Programming Software (CPS). Care must be taken not to damage the device by exceeding the maximum allowed bias voltage. The device’s drain current is drawn directly from the radio’s dc supply voltage input, A+, via L4421. 3.4 Final Stage The final stage uses the bipolar device Q4441. The device’s collector current is also drawn from the radio’s dc supply voltage input. To maintain class C operation, the base is dc-grounded by a series inductor (L4441) and a bead (L4440). A matching network consisting of C5541-C5544 and two striplines transform the impedance to 50 Ohms and feeds the directional coupler.