Table of Contents
Advertisement
R
S
P
ECEIVE
IGNAL
ATH
Incoming RF from the RX antenna jack is delivered to the
MAIN Unit and passes through the protection diode
D1001 (1SS302) and D1002 (RN739F) and a varactor-
tuned band pass filter consisting of coils L1003 and L1004,
capacitors C1012, C1014, C1015, C1017, C1018, C1021,
C1032, C1040, C1044, and C1045, and diodes D1003 and
D1004 (both HVU350). Signals are then applied to the RF
amplifier, Q1009 (2SC3357). The amplified RF signal is
applied through a varactor-tuned band pass filter consist-
ing of coils L1010 and L1011, capacitors C1071, C1074,
C1075, C1079, C1082, C1086, C1092, C1094, C1095, and
C1097, and diodes D1005 and D1007 (both HVU350) to
the first mixer Q1018 (SPM5001) along with the first lo-
cal signal from the PLL circuit.
The first local signal is generated between 326.65 MHz
and 396.65 MHz by the RX VCO, which consists of FET
Q1048 (2SK508) and varactor diodes D1018 and D1019
(both 1SV282) or FET Q1049 (2SK508) and varactor di-
odes D1020 and D1021 (both 1SV282), according to the
programmed receiving frequency; the local signal then
passes through buffer amplifier Q1059 (2SC5226) and first
local amplifier Q1019 (2SC3357) to the first mixer Q1018
(SPM5001).
The 73.35 MHz first IF signal is applied to monolithic crys-
tal filters XF1001/XF1002 (for Wide) or XF1501/XF1502 (for
Narrow) which strip away unwanted mixer products, and
the IF signal is applied to the first IF amplifiers Q1022
(2SC5226: for Wide) or Q1502 (2SC5226: for Narrow).
The amplified first IF signal is then delivered to the FM IF
subsystem IC Q1028 (TA31136FN), which contains the sec-
ond mixer, second local oscillator, limiter amplifier, noise
amplifier, and FM detector.
The second local oscillator signal, generated by the 72.895
MHz crystal X1002, produces the 455 kHz second IF sig-
nal when mixed with the first IF signal within Q1028
(TA31136FN). The second IF signal passes through ceram-
ic filter CF1001 or CF1002 which strips away all but the
desired signal, and then passes through the limiter am-
plifier within Q1028 (TA31136FN) to ceramic discrimi-
nator CD1001, which removes any amplitude variations
in the 455 kHz IF signal before detection of speech. The
detected audio passes through the low pass filter, consist-
ing of R1199 and C1244, which rejects the 455 kHz IF com-
ponent.
The audio signal from the MAIN Unit is delivered to the
CNTL Unit and passes through the audio amplifier Q1020
(NJM2904V) to the active high pass filter section of Q3020
(FX805LG), which rejects the sub-audible frequency com-
ponent. The filtered audio signal is delivered to electron-
ic volume Q1056 (M51132FP), which adjusts the audio
sensitivity to compensate for audio level variations, then
Circuit Description
passes through audio amplifier Q1020 (NJM2904V), au-
dio switch Q1040 (BU4066BCFV), attenuator consisting
of R1233, and limiter amplifier Q1050 (NJM2904V), to the
electronic volume control Q1056 (M51132FP), where the
maximum deviation is set. The audio signal subsequently
passes through the 3-section active low pass filter consist-
ing of Q1017-1/-2/-3 (NJM2902V) and audio amplifier
Q1001 (NJM2902V) to providing the repeater transmit au-
dio.
A portion of the audio signal from the active high pass
filter section of Q3020 (FX805LG) is de-emphasized con-
sisting of Q3036 (TA75S01F), R3095, and C3080, provid-
ing a flat audio response. The filtered audio then passes
through the active band pass filter Q3021 (NJM2902V)
and audio mute gate Q3015 (DTC323TK) to audio power
amplifier Q1057 (TDA2003), providing up to 2 Watts of
audio power to the 8 Ohm loudspeaker.
S
-A
S
UB
UDIBLE
IGNALING
A portion of the audio signal from the audio amplifier
Q1020 (NJM2904V) passes through the 3-section active
low pass filter Q1025 (NJM2902V) and the low pass fil-
tering section of Q3020 (FX805LG) to separate the CTC-
SS tones from the received audio signal. The CTCSS tones
are sent to the CTCSS decoder section of Q3020
(FX805LG). When a CTCSS tone is received, the CTCSS
information is delivered to pin 77 of the Main CPU Q3014
(HD64F2238) from pin 4 and 8 of Q3020 (FX805LG) which
compares the CTCSS tone with the programmed tone.
Another portion of the audio signal passes through the 3-
section active low pass filter Q3044 (NJM2902V) to sepa-
rate the DCS codes from the received audio signal. The
low pass filtered signal passes through the phase detector
Q3044 (NJM2902V) to pin 39 of the Main CPU Q3014
(HD64F2238). When a DCS code is received, the Main
CPU Q3014 (HD64F2238) compares the DCS code with
the programmed code.
If the received CTCSS tone or DCS code matches the pro-
grammed tone or code, pin 4 of the Main CPU Q3014
(HD64F2238) goes low, turning off the squelch switch
Q3015 (DTC323TK) and passing the received audio sig-
nal to the audio power amplifier Q1057 (TDA2003V).
S
C
QUELCH
ONTROL
The squelch circuit consists of noise amplifier Q1033
(2SC4116GR) and noise detector D1015 (MA143) on the
MAIN Unit, and control circuitry within Main CPU Q3014
(HD64F2238) on the CNTL Unit.
When no carrier is received, noise at the output of the au-
dio detector stage of Q1028 (TA31136FN) is amplified by
Q1033 (2SC4116GR), and then rectified by D1015 (MA143)
to provide a DC control voltage for the squelch switch.
( D
)
ECODER
F-1
Advertisement
Table of Contents
