Marti RPT-30, Руководство пользователя

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THEORY OF OPERATION
Refer to Block Diagram Drawing No. 702-073 and appropriate Schematic Diagrams.
PRE-AMP/MIXER BOARD, 800-251
Each of the four microphone inputs is fed to a low-
noise differential op-amp (half of an NE-5532). Critical
resistors in the input circuits are low-noise, precision,
temperature stable types to obtain maximum performance
from the pre-amps. Monolithic chip capacitors are used to
filter RF voltages that may be present at the microphone
inputs. The four op-amp outputs are fed to gain pots then
resistively mixed and routed to the COMPRESSOR
BOARD.
COMPRESSOR BOARD, 800-166
Several functions are performed on this board.
Integrated Circuit IC-1 serves as a (a) pre-amp [not used
on the RPT-30, (b) pre-emphasis amplifier, (c) voltage-
controlled attenuator, (d) regulator/ripple rejection. Pre-
emphasized audio out of IC-1B is also fed to D2 - D3
which form an adjustable series peak-limiting circuit.
This circuit is adjusted to limit only audio peaks which
get past the compressor. The limiter circuit feeds a low-
pass filter (L1, C23, R46) which reduces the audio
bandwidth to that specified for the operating channel of
the transmitter. To this is mixed the output of the tone
encoder, IC-2A, which is a low-distortion Wien bridge
oscillator. This composite signal is then fed to the FM
Modulator. This audio signal is also fed to IC-2B which
amplifies it to a level suitable for a 600 ohm headphone
monitor. IC-2C is a DC amplifier the input of which is
connected to the AGC (automatic gain control) circuit and
the output of which drives the audio compression meter.
FM MODULATOR, 800-160
The modulator consists of a voltage-controlled crystal
oscillator, Q1, precision voltage regulator, IC-1, and oven
heater control, Q2. Precise frequency control is obtained
by thermally coupling components Y-1, Q1, Q2, and IC-1
to the temperature-regulated Frequency Control Module
No. 800-160-1.
MULTIPLIER BOARD, 800-163
The modulator RF output is frequency-multiplied in
the multiplier board to obtain the various operating
frequencies listed on the RPT-30 specification sheet.
The multiplication factor for various frequency bands
is as follows:
140 - 180 MHz 12 X
200 - 260 MHz 16 X
280 - 340 MHz 24 X
400 - 480 MHz 24 X
The power level at the input to the multiplier is
approximately 5 mw. and the output level is 0.9 to 1.5
watts.
RF POWER AMPLIFIER, 800-170
RF output of the MULTIPLIER BOARD is connected
to the input of the power amplifier board at a 50 ohm
impedance. Transformation of the 50 ohm input to the
base impedance of Q1 is accomplished by C1, C2, and
L1, L2, and L3. L4 and L5 provide a path for Q1 base
current and the L5 - R1 parallel circuit reduces low
frequency gain and instability. The RF output power of
Q1 is approximately 10 watts and is fed to the base of Q2
by the L-C impedance matching network shown on the
schematic. L13 and R2 reduce low-frequency gain and
instability. RF power at the collector of Q2 is matched to
50 ohms by the L-C network shown. The collector supply
to Q1 and Q2 is decoupled by L8 and C5 - C10.
OUTPUT LOW-PASS FILTER,
DIRECTIONAL COUPLER, 800-250
RF output from the RF POWER AMPLIFIER passes
through a four-section low-pass filter and directional-
coupler before reaching the output connector. The
directional-coupler is of stripline construction. The
forward power sample of this coupler is supplied to the
“RF OUTPUT” METER, and the reflected power sample
is fed to comparator IC-1A on the METER BOARD and
flashes the ANTENNA (WARNING LIGHT) LED to
indicate high VSWR. R5 and R6 calibrate the forward
and reflected power samples. Circuitry for an optional
antenna relay is provided on the board. When installed,
this relay switches the antenna from RECVR (receiver)
jack to transmitter output for two-way operation.
POWER SUPPLY, 800-249
Board 800-249 contains filter capacitors C1 and C2,
voltage adjust pot R1, and reverse polarity protection
diodes D1, D2, and D3. The unregulated output voltage
of this supply is 17 - 20 volts, and is supplied from bridge
rectifier D1. Series regulator IC-1 is located on the large