User's Manual

ManualsBrandsRELM WIRELESS CORP. - BK RADIO ManualsElectronicsVHF Mobile Transceiver

BK RADIO

Page 4-1

SECTION IV

THEORY OF OPERATION

4.1 INTRODUCTION

This section contains a description of equipment and a theory of operation for the BK Radio GMH Series

mobile radio. To aid in understanding the operation of the equipment, schematic diagrams are found in

Section VI of this manual.

4.2 EQUIPMENT DESCRIPTION

The BK Radio GMH Series radio comprises the following sub-assemblies:

4.2.1 System Board

This sub-assembly consists of core microprocessor, synthesizer, regulation, and switching circuitry. A

casting is used to shield the synthesizer area.

4.2.2 RX/TX Board

This sub-assembly consists of the RX/TX antenna switch, the receiver circuitry from the front-end through

the discriminator, and the low level transmitter line up.

4.2.3 High Level Power Amplifier Board

This sub-assembly consists of the final two stages of the transmitter power amplifier, harmonic filter, and

directional coupler.

4.2.4 Options Board

This sub-assembly consists of receive and transmit audio chains, and interfaces with both the system

board and the control board.

4.2.5 Control board

This sub-assembly consists of a control head microprocessor, switching regulator, display driver, and

audio power amplifier. It interfaces with the front panel and accessory connector.

4.2.6 VCO Board

The VCO board is a separate assembly that resides in its own shielded enclosure and interconnects with

the system board and RX/TX board.

Summary of content (7 pages)

PAGE 1
SECTION IV THEORY OF OPERATION 4.1 INTRODUCTION This section contains a description of equipment and a theory of operation for the BK Radio GMH Series mobile radio. To aid in understanding the operation of the equipment, schematic diagrams are found in Section VI of this manual. 4.2 EQUIPM ENT DESCRIPTION The BK Radio GMH Series radio comprises the following sub-assemblies: 4.2.1 System Board This sub-assembly consists of core microprocessor, synthesizer, regulation, and switching circuitry.
PAGE 2
Theory of Operation 4.3 THEORY OF OPERATION 4.3.1 System board GMH Series VHF Radio System board functions include: 1. Core Microprocessor 2. Regulation: 5.0, 8.6, 9.6, and 20.0 Volts 3. Synthesizer 4. Squelch Detection 5. CTCSS/CDCSS Decode 6. Power Control 4.3.1.1 Microprocessor Control The core microprocessor (U507) communicates with the control head microprocessor and controls radio functions such as loading the synthesizer, adjusting the deviation and receiver tuning, and CTCSS/CDCSS detection.
PAGE 3
GMH Series VHF Radio General Information Prescaler - The prescaler U602 is the first divider in the feedback path of the synthesizer. It divides the RF signal to a frequency which can be processed by the following CMOS dividers. The prescaler is a dual modulus type which allows the division ratio to be set by the synthesizer to either divide-by-128 (modulus control line high) or divide-by-129 (modulus control line low).
PAGE 4
Theory of Operation 4.3.2 GMH Series VHF Radio RX/TX Board 4.3.2.1 Receiver Buffer - Q101 is an L.O. buffer which provides approximately 15 dB of gain to supply the mixer transmitter line-up. and Front End - The preselectors are varactor-tuned direct coupled filters with impedance transformations built into the configuration. The bipolar preamp provides approximately 18 dB of gain to overcome filter losses and provides a low noise figure.
PAGE 5
GMH Series VHF Radio 4.3.3 General Information High Level PA Board 4.3.3.1 Power Amplifier The high level power amplifier consists of a driver stage with a nominal output power of 15 watts and a final stage with sufficient output power to provide 50 watts at the antenna port. Both stages utilize broadband matching networks and are operated in a class C mode. 4.3.3.2 Harmonic Filter A 9th order elliptical filter is used to attenuate harmonic components before they reach the antenna port. 4.3.3.
PAGE 6
Theory of Operation 4.3.5 GMH Series VHF Radio Control Board Control Board functions include: 1. Microprocessor Control 2. EEPROM storage 3. Regulation 4. Display Driver 5. Signaling 6. Audio Power Amplifier 4.3.5.1 Microprocessor Control U102 controls the interface between the radio and the user. During normal operation, U102 monitors the front panel and push-to-talk switches, and provides data to the display.
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GMH Series VHF Radio 4.3.6 General Information VCO Board The VCO is a varactor tuned feedback oscillator using Q1 with feedback from tapped auto transformer T1. A steering voltage is used to set the capacitance of CR1, CR10, CR11, and CR12, which in turn controls the frequency of oscillation. CR3 provides a low sensitivity input for modulating the carrier frequency. The cascode amplifier comprised of Q6 isolates the VCO from its load and provides a nominal drive level of 0 dBm in receive and transmit.