Heathkit SW-7800 - Page 38

Page
126
Heathkit
A
summary
of
the
logic
levels
for
each
band
and
logic
point
is
shown
below.
____
48210
ABCDEF"
_CHUKE
+
3
Band
Switch
—_—Divider
(MHz)
Logic
Logic
Lines
Output
43210
ABCDE
0
00000
000111
1
00001
001000
2
00010
001001
3
00011
001010
4
00100
001011
5
00101
001100
6
00110
001101
7
oo111
001110
8
01000
oo1111
9
01001
010000
10
01010
010001
un
01011
010010
12.
1100
010011
13
01101
010100
14
01110
010101
15
01111
010110
16
10000
010111
17
10001
011000
10010
011001
10011
011010
10100
011011
10101
011100
10110
011101
10111
011110
11000
011111
25
11001
100000
26
11010
100001
27
1011
100010
28
11100
100011
29
11101
100100
Input
Bandpass
Filter
Select
Each
band
filter
except
band
5
is
selected
by
apply-
ing
a
high
to
the
base
of
the
first
switch
transistor.
If
band
1
is
selected,
for
example,
a
high
logic
level
is
applied
to
the
base
of
Q314.
This
turns
the
transis-
tor
on
and
causes
its
collector
to
go
to
ground. Q315
then
has
less
than
12
volts
applied
to
its
base,
which
allows
it
to
conduct
and
pass
12
volts
to
point
U.
This
12
volts forward
biases
the switching
diodes
for filter
1
on
the
receiver
circuit
board.
Band
6
is
Logic
‘Filter
Select.
+
VCO
Points
Range
GHIKL
3456
101000
100000
Lt
01000
010000
L
11010
«001000
L
101001
001000
L
401100
000100
IL
101100
900100
I
101100
000100
11100
«000100
1
010100
000010
M
o10100
000010
M
010100
000010
M
o10100
000010
M
o10100
000010
M
oi100
«000010
M
oi100
«000010
M
oi100
000010
M
o1i00
000001
H
o100
000001
H
oi100
000001
H
o1100
00000
o11100
00000
011100
00000
011100
00000
o1100
0
0000
011100
00000
H
o11100
0
0000
H
ie
1
1
1
1
1
oi1100
000001
H
1
1
1
H
H
H
o1100
00000
H
o11100
00000
H
o1i00
0
0000
H
selected
directly
from
bandswitch
line
4,
while
the
other
bands
rely
on
logic
functions
to
select
them.
For
band
5,
a
logic
low
is
applied
from
logic
point
1,
which
is
the
result
of
the
NOR
function
of
logic
G
and
bandswitch
line
4.
This
low
turns
off
Q304
and
allows
its
collector
to
go
high.
This
turns
Q305
on
and
drops
the
base
voltage
of
Q306
to
allow
12
volts
to
appear
at
point
Y.