NB-FIX UNIT (PB- 1 96 1 )
A portion of the 8 . 9 MHz IF signal is fed through
buffer 04 10
( 2SC3 72Y)
and amplified by 0206 and
020 s
( 2SC 1 583 ).
When a carrier o f noise-free m odulated signal is
received , the IF signal is rectified by D20 1 and
D202
( 1 N60) ,
producing a DC voltage . This DC
voltage is amplified by 0202
( 2 SC3 7 2Y ) ,
which
charges C 2 1 4 , for AGC purposes. The AGC voltage
is used to control the gain of 0206 and 02o s .
When impulse-type noise is received, D203 and
D204
( 1 N60)
re ctify the IF signal , producing a DC
voltage which controls the NB swit ch 04 1 1
( 2SC3 72Y) .
Noise pulses have a very short duration, but high
a mplitude . Because of the very slow time constant
o f the C 2 1 4 / R2 1 2 discharge path, AGC voltage is
not induced by these short-duration pulses . There
fore , 020 6 and 020 5 operate at full gain , providing
maximum voltage to the base of 04 1 1 . When a
pulse is received , 04 1 1 biases D4 14 to block the
signal path momentarily . When a d esired signal and
a noise pulse are re ceived simultaneously, t he
blanking action is not impaired , because the
relative amplitude difference between the desired
signal and the noise pulse is still high . The front
p anel noise b lanker level control varies the DC
voltage applied to the b ase o f 04 1 1 .
GNDh
I
I
I
I
I
I
I
I
I
I
I
I
I
LOB
L07 C3
I
007
J202
C32 0.01
V F D
L
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1 _ _
AF UNIT (PB- 1 964)
The IF signal from pin 2 is fed through T 50 1 to the
ring demodulator, consisting of
Dso2 - Dsos
( 1 S 1 007 ) ,
where the IF signal is demodulated into
audio , using the carrier signal delivered from 0503
(2SC 1 8 1 5Y).
The carrier signal is generated by
o scillator 05 14
( 2SK 1 9GR) ,
and it o scillates at one
o f the following frequencies :
USB , CW· RX
LSB
CW·TX
8989 KHz
8 9 8 6 KHz
89 8 8 . 3 KHz
The audio signal is then amplified by audio
amplifiers 0507 ,
Osos ( 2SC 1 000GR),
and 0509
(µ PC2002) ,
delivering 3 watts of audio output to
the speaker.
The audio spectrum is shaped by an active low-pass
filter of f0
=
2 . 7 kHz, - 1 2 dB/octave .
MARKER GENERA TOR
A 2 5 kHz marker signal is provided, for alignment
and testing purposes . M arker generator 0509
( 2SC1 8 1 5Y)
generates a basic 3 200 kHz signal ,
which is divided into 2 5 kHz multiples by 0506
(MC 1 4024B ) ,
a binary counter.
- 2 5 -
