RECEIVE CIRCUIT
The receiver consists of three major circuits as follows:
a. Front-End Circuit -- Consists of a one stage preampli-
fier (with band-pass filters).
b. First Mixer and IF circuit -- A special double bal-
anced mixer is used to convert the incoming signal to
55.025 MHz first IF. This is put through a band-pass
filter (BPF) and an IF amplifier to get the desired first
IF signal.
c. Second IF (455 kHz) -- Consists of one IC and three
BPF containing the second mixer, the second IF am-
plifier, and the FM detector. The second IF output
provides the Logic section with audio output.
FREQUENCY SYNTHESIZER
The frequency synthesizer is made up of three major
modules as follows:
a. VCO Module -- The UHF band frequency synthe-
sizer has one common VCO for both transmitting and
receiving. The transmitter is modulated at both the
VCO and the VCTCXO.
b. VCTCXO Module -- The VCTCXO is a voltage con-
trolled, temperature compensated crystal oscillator
providing 13.2 MHz (12.8 MHz for switchable mod-
els) as a reference frequency with modulation capa-
bility.
c. Phase-Lock Loop -- Consists of a frequency divider
and a low current drain CMOS IC for phase compari-
son.
LOGIC CIRCUIT
The logic circuit consists of a control board assembly
with an audio processor and a LED flex assembly (M-RK I),
LCD/KB flex assembly (M-RK II & Scan) as follows:
a. Control Board Assembly -- Carries two microproces-
sors, RAM, Flash E
2
PROM, audio processor, digital
processor and I/O interconnections with the fre-
quency synthesizer. This board commands all the
functions and operation of the M-RK radio.
b. Audio Signal Processor (ASP) -- Includes transmitter
and receiver audio circuits.
c.
Digital Signal Processor (DSP) -- Includes a modem,
address decoder, and clock control circuit.
d. LED Flex Assembly (M-RK I) -- Includes LED dis-
play, rotary switch and AF volume with on/off
switch.
e. LCD/KB Flex Assembly. (M-RK II & Scan) -- In-
cludes LCD driver and processor for the display, ro-
tary switch and AF volume with on/off switch.
SYSTEM ANALYSIS
Refer to Figures 3 thru 8. The M-RK radio consists of
three major printed wire boards as follows:
• Radio Board Assembly -- carries the transmit, receive,
and frequency synthesizer circuits.
• Control Board Assembly -- supports logic control
circuits.
• LED flex Assembly (M-RK I) -- carries LEDs.
• LCD/KB flex Assembly (M-RK II & Scan) -- carries
LCD.
Interconnection of the control board with other boards
and control circuits is made with flexible circuit boards and
connectors.
Circuit illustrations shown are simplified representatives
of actual circuits. They are intended only to illustrate basic
circuit functions.
RADIO BOARD ASSEMBLY
Transmit Circuits
The M-RK transmit circuit, as shown in Figures 3 and 4,
consists of the following integrated circuit, modules.
• Power Amplifier (PA)
• LPF/DC/TR SW
Power Amplifier Module (U7)
Power Amplifier (PA) U7 is a four-stage, wideband am-
plifier module with an input and an output impedance of 50
ohms (Figure 9). The second stage of the PA module has the
dc power supplied by power set transistor Q203. The RF
power output from amplifier is connected to pin 1 of the PA
module where it is applied to the input of the RF power am-
plifier stages. The RF power amplifier stages amplify the in-
put from the Tx-Amp module to a typical power output level
LBI-38735
8
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