11
Circuit Description
Receive Signal Path
Incoming RF from the antenna jack is delivered to the
RF Unit and passes through a low-pass filter consisting of
coils L1001, L1002, and L1003, capacitors C1001, C1002,
C1010, C1011, C1012, C1013, C1014, C1015, and C1016,
and antenna switching diode D1001 (
RLS135 TE-11
).
Signals within the frequency range of the transceiver
enter a varactor-tuned band-pass filter consisting of coils
L1011 and L1014, capacitors C1043, C1044, C1064,
C1081, and C1082, and diodes D1004, D1005, D1006,
and D1007
HVC350B TRF
), then amplified by Q1013
(
2SC5006-T1
) and enter a varactor-tuned band-pass fil-
ter consisting of coils L1018, L1019, and L1020, capaci-
tors C1096, C1097, C1098, C1099, C1100, C1101, C1113,
C1114, C1115, C1116, and C1117, and diodes D1014,
D101 , and D1019 (
HVC350B TRF
), before first
mixing by Q1036 (
3SK-320 TE85L
).
Buffered output from the VCO is amplified by Q1025
(
2SC5005-T1
) to provide a pure first local signal between
395.75 and 425.75 MHz for injection to the first mixer.
The 44.25 MHz first mixer product then passes through
monolithic crystal filter XF1001, XF1002 (
HDF0028
, 5.5 kHz BW) to strip away unwanted mixer
products, and the IF signal is then amplified by Q1042
(
2SC4215Y TE85R
).
The amplified first IF signal is applied to FM IF sub-
system IC Q1048 (
TA31136FN-EL
), which contains the
second mixer, second local oscillator, limiter amplifier,
noise amplifier, and RSSI amplifier.
The second local signal is produced from the PLL refer-
ence/second local oscillator of 14.60 MHz crystal X1002.
The 14.60 MHz reference signal is tripled by Q1048, ca-
pacitor C1191, and coil L1034, and the resulting 43.8 MHz
second local signal is then delivered to the mixer section
of Q1048, which produces the 450 kHz second IF when
mixed with the first IF signal.
The second IF then passes through ceramic filter CF1001
(
ALFYM450G=K
on “Narrow” channels) or CF1002
(
ALFYM450F=K
on “Wide” channels) to strip away all
but the desired signal, and then is applied to the limiter
amplifier in Q1048, which removes amplitude variations
in the 450 kHz IF, before detection of the speech by the
ceramic discriminator, CD1001 (
CDBC450CX24
).
Detected audio from Q1048 is applied to the audio high-
pass filter, and then passes via the volume control to the
audio amplifier Q1055 (
NJM2070M-TE2
), which pro-
vides up to 1/2 Watt to the optional headphone jack or a 4-
ohm loudspeaker.
Squelch Control
The squelch circuitry consists of a noise amplifier and
band-pass filter within Q1048 (
TA31136FN
), and noise
detector D1036 (
1SS400 TE-61
).
When no carrier is received, noise at the output of the
detector stage in Q1048 is amplified and band-pass fil-
tered by the noise amplifier section of Q1048 and the net-
work between pins 7 and 8, and then is rectified by D1036.
The resulting DC squelch control voltage is passed to
pin 37 of the microprocessor Q1011 (
M37516F8HP
). If
no carrier is received, this signal causes pin 24 of Q1011
to go low and pin 20 to go high. Pin 24 signals Q1047
(
CPH6102
) to disable the supply voltage to the audio am-
plifier Q1055 (
NJM2070M
), while pin 20 holds the green
(Busy) half of the LED off, when pin 24 is low and pin 20
is high.
Thus, the microprocessor blocks output from the audio
amplifier, and silences the receiver, while no signal is be-
ing received (and during transmission, as well).
When a carrier appears at the discriminator, noise is re-
moved from the output, causing pin 37 of Q1011 to go
low and the microprocessor to activate the “Busy” LED
via Q1022 (
2SC4154-T11
).
The microprocessor then checks for CTCSS or DCS code
squelch information, if enabled. If not transmitting and
CTCSS or DCS is not activated, or if the received tone or
code matches that programmed, audio is allowed to pass
through the audio amplifier Q1055 to the loudspeaker by
the enabling of the supply voltage to it via Q1047.
Transmit Signal Path
Speech input from the microphone is amplified by Q1017
(
NJM2902V TE1
); after pre-emphasis by C1059 and R1055,
the audio is amplified in another section of Q1017.
The processed audio may then be mixed with a CTCSS
tone generated by Q1011 (
M37516F8HP
) for frequency
modulation of the PLL carrier (up to ±5 kHz from the
unmodulated carrier) at the transmitting frequency.
If a DCS code is enabled for transmission, the code is
generated by microprocessor Q1011 and delivered to
D1031 (
HVC350B TRF
) for DCS modulating.
The modulated signal from the VCO Q1040 (
2SC4227-
R34
) is buffered by Q1025 (
2SC5005-T1
).
The low-level transmit signal then passes through the
T/R switching diode D1016 (
DAN235E-TL
) to buffer
amplifier Q1020 (
2SC5005-T1
), driver amplifiers Q1014
(
2SC3357-RF
) and Q1009 (
2SK2973-T13
), then the
amplified transmit signal is applied to the final amplifier
Q1006 (
2SK2974-T11
), which delivers up to 5 watts of
output power.
The transmit signal then passes through the antenna
switch D1001 (
RLS135 TE-11
) and is low-pass filtered,
to suppress harmonic spurious radiation, before delivery
to the antenna.
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