500 WATT RADIOBEACON TRANSMITTER
ND2000A-02x-xx0
Page 5-8
15 January 2005
(b) Connect a shorting jumper between TB4-19
(press-to-talk) and ground.
(c) Connect an audio signal generator between
TB4-22 and TB4-23 with shield if applicable to
TB4-24 (see figure 3-3).
(d) Set audio signal generator to 1000 Hz and its
output level to 0 dBm (0.77 Volt RMS).
(e) Set
RF
switch and
MOD
switch A4S2 (A5S2) to
ON
.
(f) Set
TONE MOD%
potentiometer A4A2R20
(A5A2R20) fully counter clockwise.
(g) Verify the transmitter's RF output is the
intended carrier level, as indicated by the
dummy load's forward power indication.
(h)
AUDIO LIMITER
lamp A4DS1 (A5DS1) shall be
on.
(i) Connect an oscilloscope to
RF MONITOR
connector.
(j) Simultaneously monitor oscilloscope waveform
and increase output level of audio signal
generator to 1.0 dBm.
(k) Oscilloscope waveform indication in step (j)
shall not vary more than 5% while increasing
output level of audio signal generator.
(l) If the requirements of step (k) are not met, set
the output of the audio signal generator to 1000
Hz at 0 dBm (0.77 V RMS) and then slowly
adjust
VOICE LEVEL
potentiometer A4A2R2
(A5A2R2) clockwise until
AUDIO LIMITER
lamp
A4DS1 (A5DS1) just turns on.
NOTE
Adjust
VOICE LEVEL
potentiometer A4A2R2
(A5A2R2) very slowly. A five second time delay is
built into the audio voice limiter circuit.
(m) Repeat steps (j) and (k).
5.3.12
MODULATION DEPTH (A3E MODE)
CHECK:
Check the modulation depth when voice
and tone (A3E mode) are simultaneously transmitted
as follows:
NOTE
The intended modulation depth is determined at initial
installation. It is the modulation depth a specific
antenna system will accommodate before excessive
reflected sideband power and/or distortion is
produced. The voice/tone must be maintained at a
60/35 percent ratio, relative to the intended
modulation depth.
(a) Set switches as tabulated for
Test Setting
in
table 4-1.
(b) Verify a shorting jumper (press-to-talk) is
connected between TB4-19 and ground.
(c) Verify an audio signal generator (voice audio
input) is connected between TB4-22 and TB4-
23 with shield if applicable to TB4-24 (see
figure 3-3).
(d) Set audio signal generator to 1000 Hz and its
output level to 0 dBm (0.77 V RMS).
(e) Connect an oscilloscope to
RF MONITOR
connector.
(f) Set
RF
switch to
ON
.
(g) Verify the transmitter's RF output is the
intended carrier level, as indicated by the
dummy load's forward power indication.
(h) If
necessary,
adjust
O/P POWER
potentiometer
A4A2R48 (A5A2R48) to set transmitter's RF
output to the intended carrier level.
(i) Set
MOD
switch A4S2 (A5S2) to
ON
.
(j) Oscilloscope
waveform's modulation envelope
shall be the composite of the external voice
audio and the tone audio (A3E). Maximum
modulation peaks shall not exceed the intended
modulation depth.
(k) If the requirements of step (j) are not met, set
TONE MOD %
potentiometer A4A2R20
(A5A2R20) fully counterclockwise.
