10
TK-7102

Frequency Configuration

The receiver utilizes double conversion. The first IF is
49.95MHz and the second IF is 450kHz. The first local oscil-
lator signal is supplied from the PLL circuit.
The PLL circuit in the transmitter generates the neces-
sary frequencies. Figure 1 shows the frequencies.

Fig. 1 Frequency configuration

Receiver System

The receiver is double conversion superheterodyne. The
frequency configuration is shown in Figure 1.

■Front-end RF Amplifier

An incoming signal from the antenna is applied to an RF
amplifier (Q26) after passing through a transmit/receive
switch circuit (D31 is off) and a band pass filter (L36, L38
and varactor diodes: D25, D26). After the signal is amplified
(Q26), the signal is filtered through a band pass filter (L30,
L32 and varactor diodes: D21, D22) to eliminate unwanted
signals before it is passed to the first mixer.
The voltage of these diodes are controlled by tracking the
CPU (IC6) center frequency of the band pass filter. (See Fig.
2)

■First Mixer

The signal from the RF amplifier is heterodyned with the
first local oscillator signal from the PLL frequency synthe-
sizer circuit at the first mixer (Q21) to create a 49.95MHz
first intermediate frequency (1st IF) signal. The first IF signal
is then fed through two monolithic crystal filters (MCFs :
XF1) to further remove spurious signals.

■IF Amplifier

The first IF signal is amplified by Q19, and the enters IC5
(FM processing IC). The signal is heterodyned again with a
second local oscillator signal within IC5 to create a 450kHz
second IF signal. The second IF signal is then fed through a
450kHz ceramic filter (Wide : CF1, Narrow : CF2) to further
eliminate unwanted signals before it is amplified and FM de-
tected in IC5.
Item Rating
Nominal center frequency 49.95MHz
Pass bandwidth ±5.0kHz or more at 3dB
35dB stop bandwidth ±20.0kHz or less
Ripple 1.0dB or less
Insertion loss 5.0dB or less
Guaranteed attenuation 80dB or more at fo±1MHz
Spurious : 40dB or more within fo±1MHz
Terminal impedance 350Ω / 5.5pF

Table 1 Crystal filter (L71-0591-05) : XF1

Item Rating
Nominal center frequency 450kHz
6dB bandwidth ±6.0kHz or more
50dB bandwidth ±12.5kHz or less
Ripple 2.0dB or less
Insertion loss 6.0dB or less
Guaranteed attenuation 35.0dB or more within fo±100kHz
Terminal impedance 2.0kΩ

Table 2 Ceramic filter (L72-0993-05) : CF1

Item Rating
Nominal center frequency 450kHz
6dB bandwidth ±4.5kHz or more
50dB bandwidth ±10.0kHz or less
Ripple 2.0dB or less
Insertion loss 6.0dB or less
Guaranteed attenuation 55.0dB or more within fo±100kHz
Terminal impedance 2.0kΩ

Table 3 Ceramic filter (L72-0994-05) : CF2

Fig. 2 Receiver system

CIRCUIT DESCRIPTION
ANT
SW
RF
AMP
1st
MIX
AF
AMP
TCXO
MIC
AMP
X3
multiply
TX
AMP
PA
AMP
CF 450kHz
MCF
49.95MHz
IF SYSTEM
PLL/VCO
16.8MHz
50.4MHz
ANT
RX
TX
SP
MIC
1/2
ANT
L36,38
D25,26
BPF
Q26
RF AMP
Q19
IF AMP
IC3
AF AMP
Q21
MIX
XF1
MCF
D30,31
ANT
SW
IC3
D/A
Q6
X3 multiply
IC23
1/2 divider X1
TCXO
IC5
MIX,IF,DET
1st local
OSC (VCO/PLL)
DEO
CF1 (Wide)
CF2 (Narrow)
TV
CPU
L30,32
D21,22
BPF