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DIVIDER
AND
PHASE
DETECTOR ASSEMBLY/
OUTPUT SYSTEM ASSEMBLY
4.63
Half
Octave
Output.
1C
1 1
is
a
4
:
1
multiplexer
which,
from
the
tuning data
detected
in
106,
and
the
channel spacing
data, provides
an
output
at
IC11/9
which
turns
on
Q
22
when
operating
in
the
lower
half of the
selected range.
4.64
On
Range
1
the half
octave
output
at pin
17
is
held
In
the
low
condition
by
a
positive level supplied
by
the
Range
switch on
line RE,
which
via
diode
D14
turns off
Q
22
.
4.65
End Stop Control
.
Half octave data
at
IC11/9
is
used
to turn
Q19
on
or
off,
according
to
which end
of the
tuning
range
has
been reached.
This
is
detected by
the gates
IC17a,
b
and
d,
in
conjunction with
the
state of
Q18
and
inverter
IC17c and
a
logic signal
is
fed out
on
the appropriate
Step
Up
or
Down
line.
If,
for
example,
the
VCO
has
reached
the
bottom end
of
its
range,
Q19
will
be
turned
off
and
IC1
7b
will
be
turned on,
thus putting a 'low'
on
the
Step
Up
line
from
pin 12.
4.66
On
the instrument's 'mixer'
range (Range
1)
the 'end
stop'
information required
is
different
from the divided ranges 2
to
5.
Thus,
on
the 'mixer' range, pin
14
goes high causing the
'mixer'
range
input
to
the
ROM
to
go low
via
IC18c.
Thus
the
ROM
selects the
appropriate
new
end
stops.
OUTPUT SYSTEM ASSEMBLY
19-0843(9081)
AND
19-0949(9082),
FIG
7
.
Introduction
4.67
Referring
to circuit
diagram
Fig.
7,
the
ECL
circuitry
on
the
left
hand
side of the
diagram
is
concerned
with
division
and
filtering of
the
main
oscillator signal to
produce
the
five
frequency
ranges.
The TTL
circuitry
on
the
right
is
concerned with
amplitude modulation, a.g.c.
level setting
and
output metering.
R.F.
Input
4.6
8
The
240MHz
to
540MHz
signal
from the
main
oscillator
assembly
is
fed via socket
SKI
1
to
the
buffer amplifier
Q1
.
From
Q1
the collector
output
is
fed via
C4
to
the
Range
5
filtering
system,
and
the emitter
output via
Q2
to the
Range 4
divider IC3.
The
collector
voltage
for
Q1
and
Q2
is
connected
via the
Output
switch
SI
2
(Fig. 20)
in
the
X2
and
NORMAL
positions.
In
the
OFF
position
this
collector supply
line
is
earthed,
which
inhibits
the
r.f.
input
to
the
range
dividers
and
filters.
Range
Switching
4.69
Range
selection
is
obtained by applying
a
+12V
level
from the
Range
switch
(Fig.
20, S2 via the appropriate
range
lines
RA,
RE,
RG,
RC
and
RD),
Range
5
Filtering
and
Half
Octave
Selection
4.70
The
240-540MHz
signal
is
fed via
C4
to
two
alternative
filter
paths,
selected
by
forward
biasing either D1
or
D2,
the control information
being supplied
via the
5
octave
input
(pin
8
).
The 5 octave
data
is
obtained by
interrogation of the
Read
Only
Memory
(ROM)
in
the Divider
and
Phase Detector Assembly,
in
order
to
establish
which
half of the
Range
5 frequency
band
is
in
use.
This
\ octave
logic
is
employed
in all
the
range
filters
except Range
1
.
9081
&
9082
Vol
.
2
4-11
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