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5.2.1
lst Local Oscillator
,
This circuit is single-loop synthesizer which generates the signal of 70.545 to I 0O.4S4g
MHz ( 100 Hz step) corresponding to the receiving frequency from 90 kHz to 29 .9999 MHz
and provides that frequency to lst mixer.
The circuit consists of variable divider, phase comparator and VCO. Furthermore the
variable divider is composed of integer part and fraction. For frequency data, digits of
l O M H z t o l 0 0 k H z a r e p r e s e t i n t h e i n t e g e r p a r t a n d d i g i t s o f l 0 k H z t o 1 0 0 H 2 i n t h e
fraction.
The reference frequency is 12.5 kHz obtained by dividing the standard signal of 5 MHz
by 400. The phase comparator compares the phase between this reference signal and
variable divider output and VCO is controlled by the DC voltage corresponding to that
phase difference.
5.2.2 2nd Local Oscillator
This circuit feeds the signal of 70 MHz to the 2nd mixer. This circuit is composed of
analogue type phase comparator, 70 MHz variable crystal oscillator (VXO) and LPF. These
are in the phase-lock loop (PLL). The phase comparator compares directly the phases
between the standard signal of 5 MHz and 70 MHz, and the 70 MHz variable crystal
oscillator is controlled by the DC voltage corresponding to that phase difference. Usually
in PLL, the phases are compared between 5 MHz obtained by dividingT0 MHz signal by 14
atrd the standard signal of 5 MHz. But in this circuit, by comparing the pulse of the
wavetbrm of the 5 MHz standard signal (the pulse width is I 12 cycle of 70 MHz) and 70
MHz signal every l4 cycles of the waveform of 70 MHz signal, the phases of 5 MHz standard
signal and 70 MHz siganl are directly compared.
5 . 2 . 3 B F O C i r c u i t
This circuit operates in CIV, SSB or AUX mode, and provides the BFO signal to the
p r o d u c t d e t e c t o r . T h e f i e q u e n c y o f t h e B F o s i g n a l c a n b e a d j u s t e d b y t h e @
C L A R I F I E E k n o b .
In case of CW mode, the frequency of 455 kHz can be varied by more than +2kHz,in
SSB mode, the frequency of 456.5 kHz can be varied by more than +50 Hz, and in AUX
mode (option), the frequency of xxxx kHz can be varied by more than 150 Hz. xxxx
rneans 456.7 in FSK mode and 45 6.9 in FAX mode.
This circuit operates as the clarifier in SSB and AUX modes.
5 . 3 P A N E L S E C T I O N
The panel section is composed of liequency indicator circuit, mode and bandwidth
indicator circuit, S meter and controls. They are mounted on one printed circuit board. The
frequency indicator circuit consists of 6-digit numerical LEDs for the receiving frequency
set by ttre I rvtHZ knob u"o lTUlVe I knob.
Since bandwidth and mode selector switches are non-locked type, the switch
information is latched, and according to this latched output, LEDs for bandwidth and mode
light up. At the same time, this output controls the IF filter selector circuit in the receiving
section and BFO selector circuit in the local signal generator section.
S meter indicates the AGC voltage when the
- t 7 -
switch on the front panel is set to
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