Motorola R-2400 Operator's Manual page 37

5.
Return "Gen
On/Off"
switch to on. Increase the RF
Level by adjusting the
step
attenuator and
"RF Ver-
nier" controls until
the receiver
just
unsquelches.
a.
On the LCD, read minimum squelch sensitivity
as
uV or dBm. This
is the threshold squelch
sen-
sitivity of
the receiver.
b.
Determine the
tight
squelch
sensitivity
of
the re-
ceiver
by repeating
steps
4
and 5
with the
receiv-
er's squelch
control
set
to maximum
tightness.
6.
Enable the
receiver'sPL/DPl
squelch
circuit. Fully
open
the carrier
squelch
control.
Increase
the
RF
level
from minimuffi,
as
in
step 5,
until
the receiver's
squelch
just
opens.
On the right LCD,
read
the
coded squelch sensitivity
in uV or
dBm.
5.5.0
AUDIO POWER OUTPUT TEST
l.
Referring
to
figure 5.2, set "Function" switch to
"Gen" and modulation
to "FM". Enter the RF fre-
quency and
PL
code.
2. Adjust
the
step
attenuator and
66RF"
Vernier'
con-
trols
to l000uV (-47 dBm). Adjust the "1
KHzLvl"
control
to
60u/o
of
the rated deviation on the
KHz
scale.
LJse
the
"RF
InlOut"
connector
for this
test.
3.
Select
"DVM"
66AC"
function.
4.
Connect
a suitable resistive load that can
dissipate
the
receiver's
rated audio output,
in
place
of
the
speaker.
(If
the
receiver
is
using
a "floating"
or
"bridge" output amplifier,
connect
a
1:1 isolation
transformer
across
the
load
resistor).
Connect
a
scope
probe
to
the
service
monitor's
"Yert/SINAD/Dist" input connector and
clip
the
probe across the load resistor
or to
the
isolation
transformer.
Connect
"RF InlOut" to
the
receiver's antenna
port. Adjust
the receiver's volume control
for
the
10.
highest voltage reading on the
DVM AC
scale
which
does
not
have
clipping or other distortion in
excess
of
the
radio's
spec as
viewed on the
oscilloscope.
7.
Calculate
the
audio
formula:
Power
Out (Watts)
-
power
by the
following
(AC
volts)2
Lodd Resistance (ohms)
8.
If
the
receiver does
not produce rated audio power
output,
use
the
service
monitor's
oscilloscope and
a
oG
RrF
scope
probe to
trace
through the audio
stages
and
locate the problem.
5.6.0 AUDIO
FREQUENCY RESPONSE
l.
Use
the
keyboard
to
enter
the
frequency
and
PL/DPL
code
(if
any)
of
the receiver
under
test.
4.
Adjust the "Code Synth
Lvl"
control
for
20t/o
of
rated deviation
on the Dev
scale,
for
example:
1
KHz in
a 5
KHz
system. Select
"DVM"
on the
left
LCD
and
((AC" volts.
Connect the service
monitor's "RF
InlOut" port
to
the
receiver's antenna
port.
Connect
the
"Y
ert/
SINAD
/Dist" input
connector
to
the
receiver's
speaker
output
usin
g a
scope
probe.
If
the speaker
is
"floating",
use
an
isolation transformer to avoid
shorting the
output
stage
to ground.
Adjust
the receiver's
volume
control to obtain
a
ref-
erence
level reading
on the AC volts
scale
which
is
free
of
clipping at any frequency within the
300
to
3000
Hzband.
Return
to
I
kHz and note this
read-
ing
as
the reference
level
(in AC volts).
Refer
to the audio
response curve
in
the receiver's
service
manual. Change the Tone
A
frequency on
the
tone display
LCD to
the value
for
each
point on
the curve
to
be measured.
Maintain FM deviation at
20a/o
of
the rated devia-
tion,
as set
in
step
4. Note the audio level
at
each
frequency. The level
in
dB must be calculated
as
20
X
log(V/VREF) where
VREF is the voltage re-
corded
in
step 6.
EIA
RS-204C specifies
the frequency
response
for
NBFM
receivers
over the range
of
300H2
to
3000
Hz
as
follows:
a. Audio
response
for
receivers using loudspeakers
shall
not vary more than
+ 2
dB
or -8 dB from
a
standard
6 dB per
octave
curve,
with
reference
taken as
1000
Hz.
b. Audio
response
for
receivers
using headphones
or telephone lines shall
not vary
more
than
+ I
dB
or -3
dB from a
standard
6 dB per
octave
curve,
with
reference
taken
at
1000
Hz.
Plot
the
resulting values using 0 dB
as
the reference
and compare
them
with
the 6
dB
per octave curve in
your
receiver's service
manual
or
with the EIA
specification as
shown
on figure
5.3.
FIGURE
5.3
-RECEIVER AUDIO
FREQUENCY RESPONSE
5.
6.
'l
.
8.
9.
5.
\-
\'
6.
2.
Set
the
"Function" switch to "Gen"
and
to "FM",
step
attenuator and vernier
l000uV (-47 dBm).
3.
Select and set
Tone
A to
1000
Hz.
Set
switch
to "Cont".
modulation
controls to
modulation
5-3