AE/LZB 119 1902 R1A
CIRCUIT ANALYSIS
The portable radio is unique in the generation of the
transmit carrier. The transmit section has an offset frequency loop operating at 115.2 MHz. This means the synthesizer is operating at a frequency that is not harmonically related to the output frequency.
The radio contains five custom integrated circuits as follows:
∙DEBBIE (D601) - Has three major functions: digitizing, voice CODEC and digital to analog conversions.
∙HILLARY (D701) - Contains the microprocessor, phase digitizer, frequency discriminator and sigma/delta modulator to provide digital modulation.
∙JACQUI (N150) - Generates the transmit carrier frequency from the main VCO frequency. Generates the transmit offset oscillator frequency and provides modulation through the I/Q inputs.
∙CHERYL ( N203) - The main and auxiliary frequency synthesizers for the main VCO and the 2nd Local Oscillator (LO).
∙DIANE (N551) - Contains the 2nd mixer and the LO for the 2nd mixer. Contains a limiter circuit which provides a balanced output to HILLARY. Provides the receiver 2nd IF and the Receiver Signal Strength Indicator (RSSI) signal.
The Schematic Diagram for this unit consist of 16
sheets. Component coordinates are provided so the technician can locate different points with ease. For example: A point may be labeled
SOFTWARE
Software in the microprocessor handles basic radio controls, interfaces and system protocols. The HILLARY chip and DSP handles all modulation, demodulation and speech processing functions.
Microprocessor software consists of:
∙RAM Bootloader Software - downloaded by the PC programmer into the radio and executed. This software communicates with the PC using a full network protocol (x3.28). Serial data is transferred through the radio UART for FLASH application loading, DSP code
storage and personality storage. This software supports read/write of EEPROM data such as Tracking Data and Feature Encryption. Data compression is used to reduce FLASH application loading time.
∙FLASH Application Software - the main radio controller software. It is divided into the platform and application modules. The platform software provides the hardware level interface, operating system,
DSP software includes:
∙FM Audio Processing - Transmit
∙FM Audio Processing - Receive
∙Transmit Waveform Generation
∙Transmit Waveform Combinations
∙Demodulation/Decoding
∙Demodulation/Decoding Combinations
RECEIVER
RX Front End
The
RF Amplifier (V400)
RF amplifier transistor V400 provides typically +16 dB of gain to the RF signal. The gain of this stage is controlled by feedback voltage from IF AMP 1 transistor V500 which sets the bias of V400. The emitter voltage of V500 is connected to the collector of V400 through resistors R504 and R401, and filter capacitors C506 and C507. This voltage can be metered at TP400. The bias to the base of V400 is set by resistor R400. RF coil L401 tunes the amplifier load. The output of V400 is coupled through fixed ceramic band pass filter Z401 (Pin 1). The band pass center frequency is 938 MHz and the gain through the filter is typically
10
