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4. CIRCUIT DESCRIPTION
1. TX (Transmitter)
The VHF signal fed from the PLL unit is apmlified at
each stage from Q1 (2SC2570A) through 04 (28C2630)
and is fed to the triple seciton Low Pass Filter (LPF). More
or less than 50W is then obtained at the antenna terminal.
For harmonics,
both 2nd f and 3rd f provide better
than—70 dB.
8~|10dBm
TK-701:
The signal detected at the 04 (2SC2630) output var-
ies
the
applied
voltage
of Q3
(2SC2539)
and
Q2
(2SC2538).
This controls the antenna output from 20W
to 50W. This APC circuit is similar to that of the TK-801.
If the final transistor temperature
rises abnormally,
the
temperature protection activates to reduce the thermistor
TH 1 resistance. This reduces the standard voltage of the
APC circuit and that of the Q6 (2SB946) to reduce the out-
put power.
LPF
-idB
Fig. 4-1 Transmitter Block Diagram
2. RX (Receiver)
Receiver input supplied through the antenna terminal
passes through the low pass filter and antenna switching
circuit, and is initially VHF-filtered by BPF assembly (L20,
21).
The
filtered
signal
is
RF
amplified
by
Q10:
2SK241(GR)-1
and is further filtered by BPF L23 and L24.
This is then input to the 1st mixer Q11:
2SK125-4.
The
1st oscillator injection signal is supplied from the PLL unit
to the RXO input. This is multiplied by , filtered by BPF:
L18,L19, and coupled to the 1st mixer O11: 2SK125-4.
4-1
The ist IF signal frequency (21.4 MHz) cutput from
the 1st mixer is filtered by Monolithic Crystal filter (MCF)
Z27 and Z28:
21F15B, and is post-amplified by Q12:
2SK241(GR)-1.
This is coupled to U13:
MC3359P which
contains the 2nd local oscillator, mixer, 2nd IF amp, qua-
drature detector, noise amp and squelch switch
The 2nd local osc operates at 20.945 MHzto convert
the 1st IF from 21.4 MHz to the 2nd IF at 45§k Hz. This
2nd IF signal is filtered by ceramic filter 231: C'W455D, is
limiter amplified, and is then quadrature detected.
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