Table of Contents
Advertisement
Circuit Description
plication to RF amplifier Q1003 (2SC5277-D2-TL) and
Q1005 (2SC5277-D2-TL). The amplified RF signal is pass
through the band-pass filter to first mixer Q1010
(2SC5277-D2-TL). Meanwhile, UHF output from the
VCO-UNIT is amplified by Q1017 (2SC5374-TL) and ap-
p l i e d t h r o u g h d i o d e T / R s w i t c h D 1 0 3 5
(HN2D01FUTE85R) to mixer Q1010 (2SC5277-D2-TL) as
the first local signal. The (Narrow, 45.8 MHz: Wide) in-
termediate frequency product of the mixer is delivered to
the AF-UNIT. The TUNE voltage from the CPU on the
CNTL-UNIT is amplified by DC amplifier Q3017
(NJU7007F2-TE1) and applied to varactors D1016 and
D1017 in the variable frequency band-pass filters. By
changing the electrostatic capacitance of the varactors,
optimum filter characteristics are provided for each spe-
cific operating frequency.
(6) 47.25 MHz First Intermediate Frequency
The 47.25 MHz first intermediate frequency from first
mixers is delivered from the RF-UNIT to the AF-UNIT
through jacks J1002 and J2002. On the AF-UNIT, the IF
for AM and FM-narrow signals is passed through NAR/
WIDE switch D2001 (DAP222-TL) and D2003 (DAN222M-
T2L), and 47.25 MHz monolithic crystal filter (MCF)
XF2001 to narrow IF amplifier Q2005 (2SC4915) for in-
put to pin 16 of Narrow IF IC Q2010 (TA31136FN) after
amplitude limiting by D2002 (DA221-TL). Meanwhile, a
portion of the output of 11.7 MHz crystal X1001 on RF-
UNIT is multiplied fourfold by Q2008 (2SC4915) and
Q2009 (2SC4915) to provide the 46.8 MHz second local
signal, applied to the Narrow IF IC. Within the IC, this
signal is mixed with the 47.25 MHz first intermediate fre-
quency signal to produce the 450 kHz second intermedi-
ate frequency.
This second IF is filtered by ceramic filter CF2002 and
amplified by the limiting amplifier within the Narrow IF
IC before quadrate detection by ceramic discriminator
CD2001. Demodulated audio is output from pin 9 of the
Narrow IF IC through narrow mute analog switch Q2019
(2SJ364-R) and squelch gate Q2020 (2SC4617 TL R) be-
fore de-emphasis.
The resulting audio is amplified by AF amplifier Q2028
(TDA7233D-TR) and output through MIC/EAR jack J2001
to internal speaker SP3001 or an external earphone.
8
(7) Squelch Control
Signal components in the neighborhood of 15 kHz con-
tained in the discriminator output pass through an active
band-pass filter composed of R2041, R2043, R2044, C2049,
C2055 and the operational amplifier between pins 7 and
8 within Narrow IF IC Q2010 (TA31136FN). They are then
rectified by D2006 and D2007 (both DA221-TL) to obtain
a DC voltage corresponding to the level of noise. This volt-
age is input to pin 51 of CPU Q3032 (HD64F2266TF13),
which compares the input voltage with a previously set
threshold. When the input voltage drops below the thresh-
old, normally due to the presence of a carrier, turning on
squelch gate Q2027 (2SJ364-R) and allowing any demod-
ulated audio to pass. At the same time, Q3001 (DTC144EE
TL) and/or Q3005 (DTC144EE TL) and/or Q3006
(DTC144EE TL) goes on, causing the BUSY/TX lamp
D3001 and D3012 to light.
Transmitter Signal Flow
(1) Transmit/Receive Switching
Closing PTT switch S2001 on the AF-UNIT pulls the
base of Q3007 (DTA144EE TL) low, causing the collector
to go high. This signal is input to pin 45 (PTT) of CPU
Q3032 (HD64F2266TF13), allowing the CPU to recognize
that the PTT switch has been pushed. When the CPU de-
tects closure of the PTT switch, pin 9 of Q3020 (TX)
(BU2099FV-E2) goes high. This control signal is deliv-
ered to the RF-UNIT, where it switches Q1039 (2SA1774
TL R) and Q1040 (2SA1774 TL R) to produce the TX con-
trol signal that activates Q1031 (2SA1774 TL R). At the
same time, PLL division data is input to PLL IC Q1020
(MB15A01PFV1-G-BND-EF) from the CPU, to disable the
receiver power saver. Also, switching Q1030 (EMB3 T2R)
to disable the receiver circuits. Then causing the red side
of BUSY/TX lamp D3011 to light.
(2) Modulation
Voice signal input from either built-in microphone
MC3001 on CNTL-UNIT or external jack J2001 on the AF-
UNIT is pre-emphasized by C3014 and R3031, and pro-
cessed by microphone amplifier and IDC (instantaneous
deviation control) circuit Q3008 (NJM3403AV-TE1) to
prevent overmodulation, and active low-pass filter sec-
tion of Q3008 (NJM3403AV-TE1).
Advertisement
Table of Contents
