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LOGIC
PCB
ASSEMBLY
4.26
Operation
of the
Range
switch
downwards
from
Range
5
also
causes a
doubling of
the
number
of pulses released
for
each
range,
to
obtain a given output frequency
step,
because
of the
f2
stages
introduced
by
the
Range
switch
into
the
main
oscillator
output.
Table 2 shows
the relationship
between
channel spacing, range
selection
and
pulses released.
TABLE
2
Channel Spacing
Control
CHANNEL
SPACINGS
Number
of
300kHz
pulses released
for
each
Spin
Wheel
Pulse
on
different
frequency
ranges.
(kHz)
Ranges
5
4
3
2
1
5
<
6.25
,
1
2
4
8
2
10
12.5
J
15
2
4
8
16
4
20
;
25
30
4
8
16
32
8
5°
:
60
:
8
16
32
64
16
Channel Spacing
Control Circuit
4.27
Consider
first
the
operation
in
Slow Tune
mode
with
Af
selected.
In
Af
mode
one
pulse at pin 18
is
obtained
for
each
pulse
from
the spin
wheel
(or
each
movement
of the Step switch
in
Hold mode)
irrespective of
range
selection.
4.28
With Channel Spacing
switch
S4
at
Af
the
line
from
pin
27
is
open
circuited,
which
turns off
Q2
and
puts a
'O'
on IC15b/5.
With
switch S6
on Slow Tune,
the
'T on
pin 24, inverted
in
IClOd, sends
IC15b/4 and hence IC10c/8
to
'O',
which
disables
IC10 and
inhibits
anyjxitput from
the
channel spacing
circuit IC6, IC1
1
and
IC14.
The
'1
1
at
IC10c/10
sets
the 'Q'
output of IC7b
to
'1
1
via the
'K'
input
on
the positive
edge
of the
clock
pulse.
4.29
Meanwhile
each
pulse
at
the
output
of
IClOb
clocks IC7a, giving a
'1'
into
the
J'
input
of IC7b.
This
allows IC7b
to
change
state
on
the positive
transition
of
the
300kHz
reference input
at
IC7b/13.
The
resulting
change
of
state at the
'Q'
output
of
IC7b
(from
'O'
to
'1')
resets
IC7a; at the
same
time
the
'O'
produced
at the
Q
output of IC7b
enables
the
gate IC9d/13,
and
allows the
300kHz
reference
signal
to
pass
to
the
'pulse'
9081
&
9082 Vol
.
2
4-5
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