Tone Squelch Unit - Icom IC-2GA Service Manual

SECTION
1
1
UT-40
TONE SQUELCH
UNIT
11-1
UT-40 CIRCUIT
DESCRIPTION
{1}
GENERAL
fCI
Is
a
tone encoder/decoder which outputs
and
detects 37
tone frequencies. IC2 functions as a serial/parallel
conver-
ter.
6-bit parallel
data are applied
to IC1.
Refer to the
following
table for
tone frequencies
and corresponding
Input data.
OUTPUT
fREQUENCy
im
CltmiTRNf^MBER OUTPUT
FREOUENCY
fci
mnn
m
number
3 4 5
8
7 3
4
6 6 7 8
67-0
H
L
H H H
L
136.5
H H H H
L
H
71-9 L L
H
H H
L 141.3 L
H H H
L
H
74.4
H H
L
H H
L 146.2
H
L
H
H
1
H
77.0
L
H
L
H H
L 151.4 L L
H H
L
H
79.7
H L L
H H
L
156.7
H
H
L
H
L
H
82.5 L L L
H
H
L 162.2 1
H
L
H
L
H
85.4
H H H
L
H
L 167.9
H
L L
H
L
H
88-5
t
H H
L
H
L 173.8 t L L
H
t
H
91.5
H
L
H
1
H
L 179.9
H H H
L L
H
94.8
H
L L
H H
H
186.2
L H
H
L L
H
100.0
j
L
L L H
H
1
H
j
192.8
H
;
L
H
L
i
L
j
H
103.5
H
H
H
L
H
;
H
203.5
3
L
H
L
L
H
107.2
L
H
;
H
L
H H
210.7
H H
L L
L
H
110.9
i
H
L
H
1
H H
218.1
L
H
L
L L H
114.8 L L
H
L
H H
225.7
H
L L L L
H
118.8
H
H
L
H H
233.6
i
L L L
:
L L
H
123.0 L
H
L L
H H
241.8
H H H
H
H
L
127.3
H
L L L
H
H
260.3 L
1
H H
H H
L
131.8
L L
L
:
L
H H
- -
—
- - -
(2)
ENCODER
IC1 {pin 26)
outputs the
programmed tone frequency
when
IC1 (pin
12)
becomes "LOW."
Q4
functions as a buffer
amplifier.
The
collector of
Q4
outputs the tone
signal
which
Is
applied to
the
VCO
circuit
to
be modulated.
Tone
deviation
is
adjusted with RIO.
(3)
DECODER
The
detected tone
from
the transceiver
Is
applied to 1C1
{pin
29).
When
the
signal
is
tone
modulated and the tone
equals the
programmed
tone frequency, pin 23
becomes
"HIGH."
When
the tone squelch function
is
turned
off,
IC2 (pins
11
and
12)
are
"HIGH."
H-5
V
are not applied to
IC1.
Q2 and
Q3
are turned
off
and
the
TSQL
line is
"HIGH."
When
the tone squelch function
is
turned
on, IC2 (pin 11)
Is
"HIGH" and
IC12 (pin 12)
is
"LOW." Q2 and Q3
are
turned
on.
When
the received tone frequency equals the
programmed
tone frequency, pin 23
is
"HIGH" and
the
TSQL
line
is
"HIGH."
When
the received
tone frequency does
not equal the
programmed
tone frequency,
IC1 (pin 23)
is
"LOW," and
the
TSQL
line
is
"LOW."
11-1