8
Circuit Description
On the PA Unit, the low-level RF signal from the
MAIN Unit is amplified by pre-driver Q2001
(RD06HHF1), push-pull driver Q2008/Q2009 (both
RD16HHF1), and push-pull final amplifier Q2012/
Q2013 (both SD1405), which provides up to 120
watts of RF output power.
The RF output from the final amplifier is fed through
the one of seven low-pass filters, sampling direc-
tional coupler T2005, and TX/RX relay RL2009 be-
fore delivery to the antenna jack.
The sampling directional coupler senses forward
and reverse power output, which is rectified by
D2017 and D2018 (both MA729), respectively, and
the DC voltage is then amplified by Q2015
(LM2904PW) on the PA Unit.
The DC voltages derived from forward and reverse
power are applied to J1003 on the MAIN Unit, and
then amplified by Q1040 (LM2904PW) and Q1044
(2SC2812). The amplified DC voltage is fed back to
the 2nd gate of the 45.275 MHz IF amplifier Q1043
(3SK151GR), so that the transmitter’s IF gain can
be regulated by this sensing of the power output,
preventing overdrive or damage caused by trans-
mission into an excessive impedance mismatch at
the antenna.
PLL Circuit
The PLL local signal for the receiver 1st local and
the transmitter final local is generated by one of two
VCOs: Q1072 or Q1073 (both 2SK210GR) in con-
junction with varactor diodes D1047, D1048, D1049,
D1050, D1051, D1052, D1053, and D1054 (all
HVU359) on the MAIN Unit. The oscillating frequen-
cy is determined primarily by the level of DC volt-
age applied to the varactor diodes. The VCO output
is buffered by Q1066 (2SK302Y), amplified by Q1074
(2SC2714Y), and band-pass filtered by capacitors
C1389, C1391, C1397, C1400, C1409, and C1420 and
coils L1070, L1071, L1074, and L1076. The filtered
PLL local signal is fed through buffer amplifiers
Q1027 (2SC2714Y), Q1028 (2SC3356), and Q1029
(2SC2954) to the TX final mixer or RX 1st mixer
D1032 (HSB88WS).
A portion of the output of buffer amplifier Q1066
(2SK302Y) is further amplified by Q1064
(2SC2714Y), then delivered to the PLL subsystem
IC Q1056 (ADF4001BRU), which contains a refer-
ence divider, serial-to-parallel data latch, program-
mable divider, phase comparator and a swallow
counter. The sample VCO signal is divided by the
programmable divider section of the Q1056
(ADF4001BRU). Meanwhile, the output from the
22.625 MHz TCXO reference oscillator, X1003, is
amplified by Q1062 (TC7S04FU) and divided by the
DDS IC Q1060 (AD9833BRM) in accordance with
the PLL dividing data from the main CPU, Q1018
(HD64F2134), then fed through the buffer amplifi-
ers Q1063 (2SC2714Y) to ceramic filter CF1001. The
divided and filtered reference signal is applied to
the reference divider section of the PLL subsystem
IC Q1056 (ADF4001BRU), where it is divided by 25/
26 to produce the loop reference.
The divided signal from the programmable divider
(derived from the VCO), and that derived from the
reference oscillator, are applied to the phase detec-
tor section of the PLL subsystem IC Q1056
(ADF4001BRU), which produces a pulsed output
with pulse duration depending on the phase differ-
ence between the input signals. This pulse train is
fed through the loop filter, consisting of resistors
R1222, R1233, & R1247 and capacitors C1278, C1284,
C1298, C1308, & C1418, then fed back to the VCO
varactor diodes D1047, D1048, D1049, D1050,
D1051, D1052, D1053, and D1054 (all HVU359).
Changes in the DC voltage applied to these varac-
tor diodes affect the reactance in the tank circuit of
VCOs Q1072 and Q1073 (both 2SK210GR), chang-
ing the oscillating frequency according to the phase
difference between the signals derived from the
VCO and the TCXO reference oscillator. The VCO
is thus phase-locked to the reference frequency stan-
dard.
A portion of the output of reference signal from
TCXO X1003 is multiplied by four at Q1070
(2SC2714Y). The resulting 90.5 MHz signal is buff-
ered by Q1075 (2SC2714Y), then applied to a low-
pass filter, consisting of capacitors C1401, C1405,
C1410, C1411, and C1421 and coils L1075 and L1077.
The filtered reference signal is applied to the TX 1st
mixer Q1054 and RX 2nd mixer Q1052 (both
RF2713).