2-2
THEORY OF OPERATION
2.0
Low Band Receiver
2.1
Receiver Front-End
The low band receiver is bandsplit into three ranges depending on radio model, covering frequencies
from 29.7 to 36.0 MHz, 36.0 to 42.0 MHz, or 42.0 to 50.0 MHz. The circuitry of the three models is
identical except for component value differences. The receiver consists of five major blocks: front-end
bandpass filters and pre-amplifier, first mixer, high-IF and blanker switches, low-IF and receiver back-
end, and “Extender” (noise blanker). Two fixed-tuned bandpass filters perform antenna signal pre-
selection. A cross over quad diode mixer converts the signal to the high-IF of 10.7 MHz. High-side
first injection is used.
Figure 2-1
Low Band Receiver Block Diagram
Demodulator
Delay
Filter
Mixer
Fixed
Tuned Filter
RF Amp
Tuned Filter
Pin Diode
Antenna
Switch
RF Jack
Antenna
First LO
RXINJ
Recovered Audio
RSSI
IF
Second LO
Crystal
Filter
455kHz Filter
455kHz Filter
455kHz Filter
(12.5kHz)
455kHz Filter
(12.5kHz)
Switch
Switch
Switch
Switch
Limiter
IF Amp
IF Amp
Filter Bank Selection
from Synthesizer IC
Blanker
Noise
Blanking Pulses
Gate
Buffer
Enable
1st
Fixed
(25/20kHz)
BWSELECT
(U1201 Pin 48)
4-pole
(25/20kHz)
Summary of Contents for 6864115B62-C
Page 1: ...Professional Radio GM Series Detailed Service Manual 6864115B62 C ...
Page 2: ...ii ...
Page 4: ...iv ...
Page 5: ...Professional Radio GM Series Service Maintainability Issue July 2007 ...
Page 8: ...ii ...
Page 22: ...2 10 MAINTENANCE ...
Page 25: ...Professional Radio GM Series Controlhead Service Information Issue July 2007 ...
Page 77: ...Professional Radio GM Series Controller Service Information Issue May 2007 ...
Page 100: ...2 2 TROUBLESHOOTING CHARTS ...
Page 104: ...3 4 Controller schematics parts list ...
Page 154: ...3 52 Controller T12 Schematic Diagrams ...
Page 155: ...Professional Radio GM Series VHF 136 174MHz Service Information Issue May 2007 ...
Page 164: ...1 6 MODEL CHART AND TECHNICAL SPECIFICATIONS ...
Page 176: ...2 12 THEORY OF OPERATION ...
Page 186: ...3 10 TROUBLESHOOTING CHARTS ...
Page 190: ...4 4 VHF PCB SCHEMATICS PARTS LISTS ...
Page 252: ...4 66 VHF 1 25W PCB 8471235L02 Schematics VHF 136 174 MHz IF ...
Page 256: ...4 70 VHF 1 25W PCB 8471235L02 Schematics ...
Page 257: ...Professional Radio GM Series UHF 403 470MHz Service Information Issue May 2007 ...
Page 266: ...1 6 MODEL CHART AND TECHNICAL SPECIFICATIONS ...
Page 366: ...2 12 THEORY OF OPERATION ...
Page 372: ...3 6 Low Band TROUBLESHOOTING CHARTS ...