Noise Blanker
The noises contained in the RF signal at the output of RF amplifier, Q20, is fed through C112 to
the base of Q23. The amplified signal output of Q20 is rectified by diodes D20 and 21. Theresult-
ing DC voltage turns on Q24 [FET] which in turn turns on Q25 and 26. This causes the IF signal
[10.695 or 10.692 MFIz] at T10 to be conducted to ground through Cl 21 and Q26 during the pré
sence o f the noise impulses, blanking out the noise from the audio output.
'Tune' Circuit (PTOS006)
The 'Tune' control facility allows between-channel operation shifting both the transmit and receive
frequencies 4.5 kHz above or below the assigned channel frequency continuously.
The active éléments of the circuit are variable-capacitance diodes D4, D5 and VR4. Both diodes
capacitances vary in accordance with the bias level determined by VR4 adjustment, thus increasing
or decreasing the parallel capacitance to R14 at Q4 emitter through C25 (by D4) and the external
capacitance to X1, X2 or X3 (by D5) simultaneously. The bias of both diodes is fixed when VR4 is
pulled to
Off.
Clarifier Circuit
The Clarifier is operative only in receive mode and changes the receive frequency regardless of the
transmitting frequency. VR6 acts to vary the plus bias voltage of D206 (on circuit board Y3) in the
same way as in Tune circuit description. Thus, Q4 oscillating frequency is pulled above (VR6 clock-
wise rotated) or down (VR6 counterclockwise rotated) its normal channel frequency. D206 is fixed
biased when the unit is transmitting.
High Filter
The high-frequency-cut filter acts to improve readability in congested areas etc., eliminating high fre
quency noise component in audio output. In PTSW072 circuit board, Q702 serves to compensate
CR filter loss.
Power Supply
The supplied 220V AC is stepped down through T201 and rectified by bridge rectifiers D1 to 4 on
PTPW007. When the voltage output at pin #3 on the circuit board decreases, the collector current
of Q2 also decreases causing reduced collector voltage. This will increase Q1 bias and Q201 bias. The
voltage across the collector to emitter of Q201 decreases thus restoring the initial voltage incline.
Adjustment
Test Equipment
The following equipment are required for servicing:
1. A 50 Ohm résistive antenna load, 20W.
2. A frequency counter operable in the required range.
3. A H F signal generator operable over 50 kHz to 60 MHz.
4. An oscilloscope.
5. An FM déviation met er.
6. A digital Voltmeter.
7. An 8 Ohm 5W résistive speaker load.
8. Two audio signal generators, 10 Hz to 20 kHz.
9. An RF Voltmeter.
10. A circuit tester, input impédance 20 kOhm/V.
11. A 220V 50 Hz AC power source.
12. Dummy microphone plug (wired as shown beside applicable set-up).
To activate the transmitter without using the microphone PTT bar, use the dummy plug. This
plug is also used to introduce a modulating audio signal to the microphone input circuit as des-
cribed in the following procedures.
Précautions
Before performing any adjustment, check visually ail jacks, plugs and solder joints for normal con
nection. Shown in the schematic diagram are nominal tested voltage values for the transistors and ICs.
For tune-up and servicing, be sure to use identical parts as listed in the
Replacement Part List.
Power Supply Alignment
Important:
This alignment should be performed first of ail items.
1) Connect circuit tester across the terminal #3 (plus) and G (minus) on PTPW007.
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