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4. Power Supply Circuit
The battery power (+B) is supplied from the battery ter-
minal to the TX-RX unit through a 3A fuse. The power (SB)
that passes through the power supply are routed to three
AVR ICs (IC702, IC704, IC705), the DC/DC converter IC
(C402) and the power transistor switch (Q5,Q6 : Control
unit) for the audio amplifier IC. It is then reduced to 3.8V by
the DC/DC converter IC and the signal goes to the three
AVR ICs (IC403, IC404, IC405).
5C is common 5V. Unless SAVE is set to OFF, 5V is al-
ways output. 5R is 5V for the receive circuitry and 5V is
supplied to the RF receive circuit during reception. 5T and
5TB are 5V for the transmit circuitry and 5V is supplied to the
RF transmit circuit during transmission. 5M supplies 5V to
the shared circuits. 33D mainly provides 3.3V to the micro-
processor (IC507), DSP (IC611) I/O section and memory IC
(IC508). 25D supplies 2.5V to the DSP core. 33A mainly
supplies 3.3V to the A/D converter IC (IC609) for reception
and the codec IC (IC608). 33AR provides 3.3V to the 2nd IF
amplifier (IC302) for reception.
The power (Vp) switched from the SB by Q5 and Q6 (con-
trol unit) supplies approx. 7V to the audio amplifier IC (IC1).
The transmit power amplifier power supply (Vd) provides
approx. 7.2V from +B through the 3A fuse and current de-
tection resistor.
5. Receiver System
5-1. Front-end RF Amplifier
The signal are passed through an antenna matching coil,
where the high-frequency components are amplified by a
dual gate FET (Q302). The signals are then fed through the
band-pass filter (L302, L307) to reject unwanted signal com-
ponents, and is fed to the 1st mixer.
5-2. First Mixer
The 1st mixer uses the IC (IC301). The 1st mixer mixes
the signal with the signal 1st local oscillator frequency from
the VCO, and converts it to the 1st IF (44.85MHz).
The signal then passes through monolithic crystal filter
(XF301) to remove unnecessary nearby frequency compo-
nents. The signal from the MCF is used as the 1st IF signal.
Item
Nominal center frequency
Pass bandwidth
Attenuation bandwidth
Ripple
Insertion loss
Guaranteed attenuation
Terminating impedance
Table 1 Crystal filter XF301 (L71-0588-05)
CIRCUIT DESCRIPTION
Rating
44.85MHz
± 5 to 7kHz at 3dB
± 25kHz or less at 30dB
1.0dB or less
4dB or less
80dB or more at fo± 910kHz
40dB or more within fo± 1MHz
350Ω/4.5pF
+B 7.5V
3A FUSE
Q702
Power SW
5M
SB
5V
IC705
AVR IC
33D
3.8V
IC402
IC405
DC/DC IC
AVR IC
5V
25D
IC401
IC404
REG
AVR IC
33A
IC403
AVR IC
5RC (Shift Register)
IC701 (6 pin)
5V
IC702
AVR IC
5TR
FET SW
5TBC (Shift Register)
IC701 (14 pin)
5C
5V
IC704
AVR IC
5CC (Shift Register)
IC701 (7 pin)
7V
Q5,Q6
Tr SW
AMP SW (Shift Register)
IC701 (4 pin)
Fig. 3 Power supply circuit
L302
L307
BPF
BPF
Q302
RF AMP
XF301
MCF
Q304
1st IF AMP
X301
OSC
44.395MHz
Fig. 4 Receiver system
TK-5400
7.2V
Vd
5M
3.3V
33D
2.5V
25D
3.3V
33A
Q306
33AR
FET SW
Q709
5R
FET SW
Q714
5TB
5T
Q712
5T
Tr SW
5TC (Shift Register)
IC701 (5 pin)
5C
Vp
IC301
1st MIX
T/R
SW
CF302
IC303
MIX, IF AMP
CF301
9
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