Motorola R-2400 Operator's Manual page 39

Place the pick-up loop
in
close
proximity
to
the
receiver
so
that the local oscillator
signal is coupled
to
the monitor input.
Using
the
frequency error
function, adjust the local oscillator for the
desired
frequency.
Change
the "Function"
switch
to "Hi
Gen"
and
enter the proper carrier frequency. Introduce suffi-
cient signal level
into the RF input to fully quiet
the
receiver
and adjust the discriminator
to
zero
volts
DC for
receivers
requiring
such an
adjustment.
For
receivers
with quadrature or more critical
detectors,
adjust detector
tuning control or local oscillator in-
jection
frequency
for
minimum distortion
or
best
SINAD performance.
For pagers
with the battery
saver
feature, check the
local oscillator
for
pulse operation without
remov-
ing the unit from it's housing.
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FIGURE 5.6-TRANSMITTER TESTS
SETUP
5.10.0 BASIC FM TRANSMITTER
TEST:
POWER, FREQUENCY,
AND DEVIATION
A.
Basic
Terminated
Measurements
l.
Connect
the
service
monitor's
"RF InlOut"
port to
the RF output of
the
unit
under
test
and make the other connections
as
shown
in
figure
5.6.
CAUTION: For
power output measurements, connect
a
transmitter only to
the
service
monitor's
"RF InlOut"
port. Do not
connect
it
to
the
service
monitor's "An-
tennatt
port.
The
built-in RF load
dissipates
up
to
50
W for
three
minutes
and up
to
125
W for
one
minute.
If
a
technician
keys
a high-power transmitter into the monitor
for
a
time long
enough
to
threaten overheating the power-
measuring circuitry, the
system's audible alarm sounds,
warning to un-key.
Set "Function" switch
to "Pwr Mon" (Or "Pwr
Mon/Anlzr Or"), "FM",
and "Squelch" control
to threshold. Enter
the correct transmitter carrier
frequency.
Set
the
step
attenuator
to -30 dB. For low-power
transmitters,
it
may be necessary
to
reduce the
at-
tenuator setting
to
unsquelch
the monitor. Too
high an attenuator setting or too tight a
squelch
setting
inhibits the
frequency
error display. Ac-
curate
measurements
require sufficient
signal
level
from
the radio
to
fully quiet the
service
monitor's
receiver.
Use
good quality
cables
of
minimum length
be-
cause
cable-loss can be a
significant factor in RF
power
measurement, especially
at
UHF
and
above.
Key the transmitter and read the power
indicated on the display.
5.
Read
the transmitter's frequency error indicated
on the display.
Refer
to
the
radio's
service
manual
to
determine
if
power and frequency
are
within
spec
limits
and
determine
if
any adjustments are
required.
Proceed
to
check
modulation
as
follows:
a.
Turn
off
all modulation
sources
at the "Mod
Out" of
the
service
monitor in order to
check
the level
of
PL or DPL
deviation
from
the
transmitter. Switch "Function" to "Pwr Mon"
to
observe recovered audio.
b.
Key up transmitter
with
appropriate
PL
or
DPL
enabled
and read "Dev" from the left
LCD.
Refer
to radio
service
manual
to
deter-
mine
if
adjustment is
necessary.
c. With PL or DPL modulation properly
set, in-
troduce
I
KHz
modulation
to
transmitter
audio
input by adjusting
the
"l
KHzLvl"
con-
trol.
Check service manual
to
determine the
minimum level required
for proper MIC
sen-
sitivity
as
well
as
the
maximum level required
to insure proper IDC
function.
Read
"Mod
Out"
levels
on the DVM by
temporarily
switching
the
left
LCD
to
"DVM",
and
ttSourcett
to ttAC".
d.
At
the
maximum audio
input
level,
read
"Dev" on the display and verify that
it
falls
within the maximum rated system deviation
specified
in the radio's
service
manual. Make
adjustments
as
required.
e.
Verify proper MIC sensitivity by
setting
"Mod
Out" to the minimum threshold
level
per
the
service manual
and
reading
corresponding
"Dev" on the display.
Off-The-Air
Measurements
l.
Connect
the
TEKA-}
A pick up
antenna
to
the
service
monitor's "Antenna" connector.
Change
the "Function" switch
to
"Sens
Mon" (or
"Sens
Mon/Anlzr
On")
2.
Operate
the transmitter under test either into its
own antenna
or into
a
dummy RF load,
as
shown
in
figure
5.6.
3.
Set
the
service
monitor's "Squelch" control to
threshold, and enter the correct carrier frequency.
3.
2.
3.
6.
7.
4.
4.
5.
B.
5-5
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