Kenwood TM-731A Service Manual page 3

TM-731A/E
CIRCUIT DESCRIPTION
Receiver Circuits
* General
e 144 MHz
The incoming two meter band signal passes thru the trans-
mit/receive switching diode in the final unit. And then through
the antenna matching coil in the front unit. It is then amplified
by a GaAs FET radio-frequency amplifier, Filtered by a three-
stage bandpass filter that uses varicap tuning to reject unwant-
ed signal components, and is fed to the first mixer. There it
is mixed with the first local oscillator signal from the PLL to
generate the first IF signal (10.7 MHz (M,W), 16.9 MHz (K,P)).
Spurious adjacent-channel signals are removed in a two-stage
MCF (Monolithic Crystal Filter).
The first IF signal is amplified and fed to the FM IF IC:MC3361D.
This IF signal is mixed with the second local oscillator frequency
of 10.245 MHz (M,W) and 17.355 MHz (K,P} which results
in a second IF signal of 455 kHz.
Spurious adjacent-channel signals are removed from the se-
cond IF signal by ceramic filter. Then the signal is amplified
Fig. 2 144 MHz Front End [Varicap Tuning) PLL OUT
¢ 430 MHz band
The incoming 70 cm signal passes thru the transmit/receive
antenna switching diodes in the final unit and then passes
through the antenna matching coil. The signal is then fed to
a two-stage radio-frequency amplifier consisting of a GaAs FET
and a junction-type FET. It then passes through a two-stage
two-cauity helical resonator and enters the first mixer, where
it is mixed with the first local oscillator signal from the PLL to
generate the first IF signal (30.825 MHz (M,W), 21.6 MHz
(K,P)). Spurious adjacent-channel signals are removed by a
two-stage MCF. :
The first IF signal is amplified and fed to the FM IF IC
(MC3361D). This IF signal is mixed with a second local oscil-
lator frequency of 30.37 MHz (M,W) and 21.145 MHz (K,P)
|Loss ——- ==.
Item Specification
Nominal center frequency | 30.825 MHz
Pass bandwidth Max. +7.5 kHz at 3 dB
Attenuation band width
| Max.
+28 kHz at 40 dB
Ripple Max. 1.5 dB
Insertion loss Max. 3 dB
Terminating. impedance 1.4 kQ/1_ pF
item Rating
Nominal center frequency
(fo) 21.600 kHz
3 dB bandwidth +7.5 kHz or more
+25 kHz or less at 40 dB
+45 kHz or less at 60 dB
Attenuation bandwidth
2.0.dB.orless . pene
Input and output im-
pedance 1 kQ/1 pF
Table 3 MCF (L71-0227-05)
(430 MHz TX-RX unit XF1) (K,P)
Item Specification
Nominal center frequency 455 kHz+1 kHz
6 dB bandwidth Min. +6 kHz (above 455 kHz)
50 dB bandwidth Min, +12,.5 kHz (above 455 kHz)
Ripple (455 +4 kHz) Max. 3 dB
Insertion loss . | Max. 6 dB
Guaranteed attenuation
(455 +100 kHz) Max, 35 dB
input-output matching 2.0 ka
impedance
Table 4 Ceramic Filter CFW455F (L72-0315-05)
Characteristics (430 MHz TX-RX Unit CF1,
144MHz TX-RX-Unit CF1)
item Rating
Nominal center frequency
{fo} 16.900 kHz
3 dB bandwidth +7.5 kHz or more
+25 kHz or less at 40 dB
+45 kHz or less at 60 dB
Attenuation bandwidth
Ripple 1.0 dB or less
Loss 1.5 dB or less
input and output im-
pedance 1.8 kQ/O pF
Table 5 MCF (L71-0279-05) Characteristics