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86.0
89.6
93.2
96.8
L--1
/.llic Hi) and J911-3 (Mic Lo).
L-= to 2.25 KHz. Yoltage should
be
Ad-
CRYSTAL
OSCILLATOR
FREQUENCY ADJUSTMENT
First,
check the frequency to Ceter-
mine if any adjustmeni is required.
The
frequency should be set with a
frequency
meter or counter with an absolute
accuracy
that
is
5 tc 10 times better
than
the
tolerance to be naintained, and with
the
entire
radio as neat as possible to
an
ambient temperature of 27.0.C (80.6'F).
The oscillator
should be reset only
when the frequency
shows deviation
in
excess
of the following limits:
.
J0,5
PPM,
when
the radio is at
27.0'C
(80.6'F).
o
The
specification
limit of
+5
pPM
at
any
tempers
ture
c'j
thin the ranges of
-30'C
(-22'f)
ro +60"c
/-140"FJ.
If the radio is at
an
anbient
tempera-
turo
@ng
frequency.
If the radio is not at an anbient
tem-
pera
t
as a function of
actua
1 temperature, by
the
amount shown in the Fre'Auency Off-set
Cha
rt
.
For example:
Assume
the anbient
tem-
perature of the radio is 22'C (71.6'F)'
At
that tenperature, the curve
shows
a correc-
tion factor of r0.75 pPM, (At 450
tr{Hz,
1
pPlf is 450 Hz.
At 474
MHz,
1
PPII
is
470
Hz.
)
\{ith
an operating
frequency of
450
MHz, set the
osci
1
lator
for a readlng of
337.5 Hz (0.75 x
45O
Hz) higher than
the
licensed operating frequency.
1f a
nega-
tive
correction
factor
is obtained
(at
tenperatures
above
27.0'C), set the
oscj.1-
lator for the indicated
PPM
lower than
the
licensed operati.g
f
requency.
TRANSITIIT FREQUENCY
ADJUSTMENT
lqhen
setting the transmitter
oscilla-
tor frequency, adjust
L151
OR
L152 to
the
assigned operating frequency.
Always
set
the lower frequency first.
FREQUENCY
AND
UODULATION
ADJUSTMENT
TEST
EQUIPIIENT
REQUIRED
1.
Audio Oscillator
2.
Deviation
Monitor
3.
AC
Voltmeter
4.
Wattmeter, 50 ohn,
50
Watts
5.
Frequency
Counter
FREQUENCY
ADJUSTMENT
Set the transmitter
oscillator
fre-
quency by adjusting
L151 (RPT) and
L152
(DIR) to the assigned operating
frequency.
Always set the frequency flrst
before setting lhe nodrlation-
L,BI3LO72
MODULATION
LEVEL
ADJUSTMENT
A Channel Guard
Encode
Disable circult
has
been
incorporated as a
maintenance
aid
to
al
1ow the service technlcian
to
make
transmitter
distortion
and modulation
checks
without
removing
the cover fron
the
radlo.
The
CG
encode circuit
can be easily
disabled by tenporarlly
connecting a
jumper
from J910-11 (A+) to J910-9
(CG
DISABLE
lead).
MOD
ADJUST
Controls
R155
and
R156
have
been
adjusted to the proper setting
before
shipment
and normally do not require.read-
justment.
This setting
permlts approxi-
mately
75%
modulation for the
average-voice
1eve1,
PROCEDURE
1.
Connect
the audio oscitlator
and
the
AC
voltmeter across audlo input ter-
minals J911-4 (Hi) and J911-3 (Lo)
on
the
lOC board.
2.
Adjust the audio oscillator
for
RMS
at
1000
Hz.
3.
Connect
RF
Wattmeter
to
antenna
1 Volt
jack.
Set
CHANNEL GUARD MOD
ADJUST
R1O10
for
zero tone deviation,
Next, with the
1
Volt signal at 1000 Hz applied,
set
MOD
ADJUST
R155 (Fl)
for
3.75
kHz
devia
tion.
Switch to F2 and adjust
R156 for
the
same
deviation,
Then
remove the signal
from the audio
oscillator
and set
Channel
Guard
MOD
ADJUST R1010 lor
0.75
kHz tone
deviation.
If the devlation reading plus
(+)
or minus (-)
differs
more
than
0.5 kHz, recheck Step 1 as
shown
in
the
Transmi
tter
A1
ignment
Chart.
TRANSMITTER
ALIGNMENT
PROCIDURES
DO NOT
remove
microphone
from
the
optional hookswltch (if preserrt),
or place
CG
MON
switch to
MON
position
when
making
this adjust-
ment.
DAMAGE
to
equipment
will
result.
The Channet Guard modulation
I
eve
1
a
dj
ustment
shoul
d
be
checked each tlme
the
tone
frequency is
changed.
lhar
t
Issue I
15
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