Maxon Telecom SP200 First Mixer, Second mixer, Second IF, FM detector, Squelch Mute Circuit

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SP200/210

Maxon SP200/210 Radio

First Mixer

D9, T1 and T2 form a double balanced mixer which provides the 45.1MHz intermediate frequency output. The filtered frequency from the front end module is coupled to T1.

The Local oscillator input from the VCO is coupled to T2.

The output of the mixer is taken from the tap on transformer T1 and fed to the single pole diplexer, comprising L15 / C93 and R65 (High-pass terminating filter) and L14 / C92 (Low-pass coupling filter)

The 45.1MHz crystal filter provides a bandwidth of +/-7.2 kHz. This filter provides a high degree of protection from spurious and intermodulation products. Additionally, a 90 MHz trap (C93 / L15) is placed at the filter input.

The output of the filter is coupled by C43 to the base of the post filter IF amplifier Q25.

Second mixer, Second IF, FM detector

The output of the IF amplifier is fed into the narrowband FM IF Integrated Circuit, IC5 (MC3372). This is a single conversion FM receiver which contains the second mixer, second IF amplifier, and FM detector.

The second local oscillator frequency is determined by the crystal X1 connected to pin 1 of IC5. In this case the crystal has a frequency of 44.645MHz. The first IF signal is applied to the mixer and the resultant frequency of 455KHz, is the difference between the IF signal and second local oscillator.

The 455KHz IF signal is output from pin 3 and is applied to a 455KHz band-pass filter, CF1 (20/25 kHz channel spacing) or CF2 (12.5 kHz channel spacing). The selection of the filters is accomplished by diodes D13 (input) and D14 (output) whose bias is controlled by the N/S SW line on the microcontroller (IC403, pin 25).

The microcontroller takes the relevant channel spacing data from the EEPROM. A High on the N/S SW line switches the 455kHz signal to CF1, a low switches the signal to CF2.

The output of the relevant IF filter is passed to pin 5, which is the input to the limiting amplifier.

The limiting amplifier is biased externally by R19 & R95 and connected by C52 to the quadrature detector (X2). The output connects to pin 8. The quadrature circuitry provides a 90° phase shift at the IF centre frequency, which enables audio to be recovered. Any detected signal is produced at pin 9 of IC5 and applied to the Receiver Audio Circuit and the Mute (Squelch) Circuit.

Squelch (Mute) Circuit

The mute circuit switches off the audio amplifier when no audio signal is present. The squelch circuit consists of IC5 and RV2 (RV4) and their associated components. The noise signal from pin 9 of IC5 is amplified by an internal amplifier in IC5 and fed to the 16kHz bandpass filter.

16kHz Band Pass Filter

The audio signal from pin 9 of IC5 is filtered by a 16 kHz band pass filter consisting of L16, L17 / C111 to C113. The noise in the IF passband is accepted and voice frequencies and their products are rejected.

Any noise present at the output of the filter is applied to the noise detector circuit via RV2 (RV4). RV2 (RV4) is used to adjust the squelch circuit sensitivity and is normally adjusted to produce a noise squelch opening sensitivity of 10 to 12 dB SINAD.

For 12.5 kHz channel spacing, RV4 is switched in, by the microcontroller and Q28, to attenuate signal at RV2 for 25 kHz channels. A High on the N/S SW line switches in RV4.

The output from the band pass filter is applied to the filter amplifier input on pin 10 of IC5.

Issue 1.0

DETAILED FUNCTIONAL DESCRIPTION

03/01

Page 5-9

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Contents SP200/210 NSW Australia Tel +61 0 2 9707 Amendment Record Sheet Issue No Effective Date Reason for Change SignatureAmendment Record Sheet Maxon SP200/210 Radio Table of Contents 11.4 Default Settings 11-8 SL100 UHF Parts List10-1 11-1List of Tables Maxon SP200/210 Radio Issue 03/01 Introduction Using this ManualAmendments to this Manual Category C Engineering BulletinContact Information General SpecificationsPhysical Dimensions Synthesiser Environmental Operating Temperature RangeVibration ESD EMCPre-Install Check Accessories Accessories & OptionsOptions Accessories & Options Installation INSTALLATION, Commissioning & AlignmentINSTALLATION, Commissioning & Alignment ConnectionsRecommended Test Equipment CommissioningCommissioning Kit Commissioning EquipmentDiscrete Test Equipment Test Equipment Set-up using Discrete Test EquipmentSK 3100 Service Kit Transmitter Performance Tests Test Equipment ConnectionReceiver Performance Tests Squelch Power AdjustmentAudio Output Alignment Tests without DisassemblyPreparation VHFRemoving and Replacing Battery Disassembly and Re-assembly of the RadioRemoving and Replacing the Belt Clip Location of Adjustment Points Removing and Replacing the Main AssemblyPLL Alignment Transmitter Alignment Squelch SensitivityTcxo Radiocommunications Test SET Audio deviation adjustment Balance AdjustmentCtcss / DCS deviation At maximum volume, nominal distortion is 10% Audio Volume LevelReceiver Alignment Introduction Detailed Functional DescriptionCommon Circuits EepromAudio Asic Audio Signal PathMiscellaneous Signals and Controller Sat Signal PathAudio/SAT Circuits LEDs and indicators Battery Low Indicator CircuitCommon RF Circuits PLL SynthesiserOut-of-Lock Detector PLL ICCharge Pump and Loop Filter DC to DC ConverterAutomatic power control APC circuits Antenna SwitchTransmitter PA moduleFront End ReceiverSecond mixer, Second IF, FM detector First MixerSquelch Mute Circuit 16kHz Band Pass FilterAF Output Low Pass Filter Noise detector circuitSpeaker Audio Amplifier Diagnostic Function TroubleshootingDiagnostics TroubleshootingIf IC Troubleshooting ChartTransistors Main Circuit Voltage ChartsMain Circuit Transistor Voltages Integrated Circuit Voltages Receive Integrated CircuitsIntegrated Circuit Voltages Transmit Troubleshooting Troubleshooting Troubleshooting Troubleshooting SMP6100 ProgrammingIntroduction Getting StartedScanning Select Features MenuProgram/Print/Save Program RadioSave Data to Disk Print DataMaxon SP200/200 Radio SP200/210 Parts List Exploded Mechanical Drawings & Parts ListsExploded Mechanical Drawings & Parts Lists Spare PartsSL100V2 SL100U2For details on servicing, please refer to Section Mechanical PartsLCD TTR 1866 Dpfdpw Parts List for Exploded Mechanical DrawingSKPT-110VA PCB LCDSML-020MLTT86 SMD NUT M7 BsbmPCB VCO PCB RF Bsbm M2.6 AldcV2 Control Circuit SL100 VHF Parts List05B-000-5Z Chip Ceramic 0.001UF GRM39 X7R102K 50V P Diode Switching KDS181S A3Chip Ceramic 0.012UF GRM39 X7R123K 25V P Chip Ceramic 0.0022UF GRM39 X7R222J 50V PSW Tact SKPT-1101VA 2 V2 RFRES.CHIP Trimmer 10K RH03E1C14X RES.CHIP Trimmer 1K RH03E1C13XThermistor Chip 33KNTCCS32163SH333KC TH1 Elect Capacitor 10UF 16V 20%Chip Ceramic 39PF GRM40 COG390J 50V P RE Power Module GNOK-M68776-E01 IC9Chip Ceramic 43PF GRM40 COG430J 50V P Chip Ceramic 47PF GRM39 COG470J 50V PTcxo Assembly 5 V2 Front End 4 V2 VCOU2 Control Circuit SL100 UHF Parts ListConnector Waffer Chip Resistor 12K 2 U2 RFChip Resistor 18K Chip Resistor 39KChip Ceramic 0.0015UF GRM39 X7R152K 50V P RES.CHIP Trimmer K RH03E1C13XChip Ceramic 10PF GRM40 COG100C 50V P Chip CeramicChip Ceramic 2.2PF GRM40 COG2R2C 50V P Power Mpduleuhf M68732HGNOK IC9Chip Ceramic 470PF GRM40 COG471J 50V P Chip Ceramic 4.7PF GRM40 COG4R7C 50V PCoil Chip 18NHLL2012-F18NM TcxoCoil Spring X0.35X7TR Coil Spring 2X0.75X3TL SMD4 VCO Maxon SP200/210 Radio Circuit Diagrams & PCB Layouts Circuit Diagrams & PCB LayoutsRF PCB TcxoCircuit Diagrams & PCB Layouts Digital Board Layout Top Side Digital Board Layout Bottom Side RF Board Layout Top Side Issue RF Board Layout Bottom Side P406787a Front End Front-End Board Layout Tcxo Board Layout 10SPARE Parts Spare Parts & Maintenance Policy10.1Spare Parts Surface mount component replacement Component ReplacementSurface mount components Surface mount removalSurface mounted integrated circuit replacement Spare Parts & Maintenance Policy 11.1Purpose 11APPENDIX ACC-2003 Alignment BOX11.2Test Equipment 11.3Calibration ProgramAppendix a ACC-2003 Alignment BOX Calibration Program Primary ScreenAsic Control Screen Rx TXTRIM2 Adjustment of Asic valuesTXTRIM3 RX VOL SAT Balance Transmit AdjustmentsSAT Deviation Audio Output Level Receive Adjustments11.4.1 V1 Band Default Settings 11.4Default SettingsV1 Default Frequency Table V1 Default Asic SettingsV2 Default Frequency Table 11.4.2 V2 Band Default SettingsV2 Default Asic Settings U1 Default Frequency Table 11.4.3 U1 Band Default SettingsU1 Default Asic Settings U2 Default Frequency Table 11.4.4 U2 Band Default SettingsU2 Default Asic Settings
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