500 WATT RADIOBEACON TRANSMITTER
ND2000A-02x-xx0
Page 5-7
15 January 2005
NOTE
When reading modulation percentage on
TEST-
Power/Mod
meter, always set
TEST-Power/Mod
switch
to
MOD-SET
and adjust
SET 100% MOD
potentiometer
for a 100% indication before taking a modulation
depth reading.
(c) Set
MOD
switch A4S2 (A5S2) to
ON
.
(d) Connect an oscilloscope to
RF MONITOR
connector.
(e) Set
RF
switch to
ON
.
(f) Verify the transmitter's RF output is the
intended carrier level, as indicated by the
dummy load's forward power indication.
(g) If
necessary,
adjust
O/P POWER
potentiometer
A4A2R48 (A5A2R48) to set transmitter's RF
output to the intended carrier level.
(h) Set
TEST-Power/Mod
switch to
MOD-SET
.
(i) Adjust
SET 100% MOD
potentiometer for a 100%
modulation depth indication on
TEST-
Power/Mod
meter.
(j) Set
TEST-Power/Mod
switch to
MOD-READ
.
(k) Adjust
TONE LEVEL
potentiometer A4A2R19
(A5A2R19) until
TEST-Power/Mod
meter's
modulation percentage indication is 100%.
(l) Oscilloscope waveform shall be similar to the
waveform depicted in figure 6-14. Modulation
depth shall be 100% and waveform shall be free
from clipping and/or distortion.
(m) If necessary, adjust
TONE LEVEL
potentiometer
A4A2R19 (A5A2R19) for a
TEST Power/Mod
meter's indication of 95% or the intended
modulation depth.
(n) Oscilloscope waveform shall be similar to the
one depicted in figure 6-14. Modulation
envelope shall be 95% or the intended
modulation depth and waveform shall be free
from clipping and distortion.
5.3.10
B- VOLTAGE (MCW) CHECK:
Check
the B- voltage with the transmitter's RF output set to
the intended carrier level and the intended modulation
depth, as follows:
(a) Set or verify switches are set as tabulated for
Test Setting
in table 4-1.
(b) Set
RF
switch to
ON
.
(c) Verify the transmitter's RF output is the
intended carrier level, as indicated by the
dummy load's forward power indication.
(d) If
necessary,
adjust
O/P POWER
potentiometer
A4A2R48 (A5A2R48) to set transmitter's RF
output to the intended carrier level.
(e) Set
MOD
switch A4S2 (A5S2) to
ON
.
(f)
Test-Power/Mod
meter's indication should be
95% or the intended modulation depth.
(g) If necessary, adjust modulation depth as detailed
in paragraph 5.3.9.
(h) Set
TEST-Volts/Current
switch to
B- SIDE A
(
B
).
(i) Connect a multimeter between test point
A7A1TP1 (A8A1TP1) and ground.
(j) Multimeter's indication shall be precisely -50.0
V dc.
(k) If necessary, adjust
B- Adj
potentiometer
A7A1R12 (A8A1R12) until multimeter's
indication is precisely -50.0 V dc.
(l)
Test-Volts/Current
meter's indication shall be
between -49.0 and -51.0 V dc.
(m) Record difference between reading obtained in
step (l) and reading obtained in step (j) as
TEST-
Volts/Current
meter's correction factor for B-
volts (MCW) in
Established References
section
of table 5-2.
5.3.11 AUDIO LIMITER BALANCE
CHECK:
Check the audio limiter circuits as follows:
(a) Set switches as tabulated for
Test Setting
in
table 4-1.
