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500 WATT RADIOBEACON TRANSMITTER
ND2000A-02x-xx0
Page 5-5
15 January 2005
(c) Verify the appropriate link is installed on RF
oscillator A4A3 (A5A3) (PWB pad 'E'
connected to PWB pad
÷
4, 8 or 16; PWB pad
'A' connected to PWB pad 'B') for the assigned
carrier frequency.
(d) Disconnect connector A4P2 (A5P2) from its
mating connector A4A4J1 (A5A4J1).
(e) Set
RF
switch to
ON
.
RF
DRIVE ALARM
lamp
A4DS2 (A5DS2) shall turn
ON
.
(f) Connect a frequency counter between test point
A4A3TP3 (A5A3TP3) and ground.
(g) Frequency counter indication shall be the
assigned carrier frequency ± 0.004%.
(h) If necessary, adjust
Osc Freq
trimmer capacitor
A4A3C5 (A5A3C5) until the frequency
counter's indication is the assigned carrier
frequency ± 0.004%.
(i) Connect an oscilloscope between test point
A4A3TP3 (A5A3TP3) and ground.
(j) Oscilloscope waveform indication shall be
similar to the waveform depicted in figure 6-2,
with a peak-to-peak voltage between 11.7 and
14.3 volts.
(k) Set
RF
switch to
OFF
.
(l)
Connect connector A4P2 (A5P2) to its mating
connector A4A4J1 (A5A4J1)
5.3.6
RF DRIVE OUTPUT LEVEL CHECK:
Check the RF drive output level from RF drive
amplifier A4A4 (A5A4) 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) Connect an oscilloscope between center
conductor of A4A4J2 (A5A4J2) and ground.
(d) Oscilloscope waveform indication shall be
similar to the waveform depicted in figure 6-5,
with a peak-to-peak voltage between 48.0 and
52.0 volts.
(e) Connect a multimeter between connector
A4A4J3 (A5A4J3) and ground.
(f) Multimeter indication shall be between 12.0 and
14.0 V dc.
(g) Disconnect multimeter and oscilloscope.
5.3.7
PULSE WIDTH MODULATION
DRIVE CHECK:
Check the frequency and ramp
waveform of the variable pulse width modulation
(PWM) mod drive circuit, as follows:
(a) Set or verify switches are set as tabulated for
Test Setting
in table 4-1.
(b) Verify
O/P POWER
potentiometer A4A2R48
(A5A2R48) is set fully counter clockwise.
(c) Verify
PWR TRIM - LOCAL
potentiometer A4R5
(A5R5) is set fully clockwise.
(d) Set
RF
switch to
ON
.
(e) Connect a frequency counter between test point
A4A2TP5 (A5A2TP5) and ground.
(f) Frequency counter's indication shall be between
69.86 kHz and 70.14 kHz.
(g) If necessary, adjust
PWM Freq
trimmer capacitor
A4A2C22 (A5A2C22) until frequency counter's
indication is between 69.86 kHz and 70.14 kHz.
(h) Connect an oscilloscope between test point
A4A2TP6 (A5A2TP6) and ground.
(i) Oscilloscope waveform indication shall be a dc
trace (no pulses).
(j) If necessary, adjust
RAMP ADJUST
potentiometer A4A2R58 (A5A2R58) until there
are pulses on the oscilloscope trace and then
adjust
RAMP ADJUST
potentiometer A4A2R58
(A5A2R58) until the pulses just disappear.
(k) Connect oscilloscope between test point
A4A2TP5 (A5A2TP5) and ground.