500 WATT RADIOBEACON TRANSMITTER
ND2000A-02x-xx0
Page 5-11
15 January 2005
(d)
TEST-Power/Mod
meter's forward power
indication should be -3.0 dB from the intended
carrier level.
(e) If requirement of step (d) is met, go to step (k);
if not, complete steps (f) through (j).
(f) Adjust
O/P POWER
potentiometer A4A2R48
(A5A2R48) for a forward power indication on
TEST-Power/Mod
meter that is 3.0 dB less than
the intended carrier level.
(g)
If
SET THRSH
lamp A10DS1 is full on (not
flashing), adjust
CARR THRSH
potentiometer
A10R18 until
SET THRSH
lamp A10DS1 is
flashing.
(h) Adjust
CARR THRSH
potentiometer A10R18
until
SET THRSH
lamp A10DS1 just turns full
on and remains on.
(i) Adjust
O/P POWER
potentiometer A4A2R48
(A5A2R48) for the intended carrier level, as
indicated by
TEST-Power/Mod
meter.
(j)
Repeat steps (b) through (d).
(k) Adjust
O/P POWER
potentiometer A4A2R48
(A5A2R48) for the intended carrier level, as
indicated by
TEST-Power/Mod
meter.
(l)
SET THRSH
lamp A10DS1 shall be flashing on
and off.
5.3.15.3 Modulation Depth Fault Threshold
Check:
Check that the modulation depth fault
threshold is set to initiate a changeover from main to
standby transmitter when the modulation depth has
decreased by 4.0 dB or to a user determined decrease,
as follows:
NOTE
The modulation depth fault threshold (normally -4.0
dB) must be not less than -1.0 dB greater than the
carrier level fault threshold.
(a) Verify
the
instructions detailed in paragraphs
5.3.15.1 and 5.3.15.2 have been completed and
their requirements are being met.
(b) Determine the minimum modulation depth
(normally -4.0 dB when the carrier level fault
threshold is -3.0 dB) that is acceptable before
transmitter changeover occurs. Record this
level as the Modulation Depth Fault Threshold
in
Established References
section of table 5-2.
NOTE
If difference between intended modulation depth and
modulation depth fault threshold is specified in dB,
refer to table 5-1 and determine power multiplication
factor for specified dB reduction. Multiply intended
modulation depth by power multiplication factor to
determine modulation depth fault threshold.
(c) Set switches as tabulated for
Test Settings
in
table 4-1.
(d) Set
MOD
switch A4S2 (A5S2) to
ON
.
(e) Verify an oscilloscope is connected to
RF
MONITOR
connector.
(f) Set
RF
switch to
ON
.
(g) Verify the RF output is the intended carrier
level, as indicated by
TEST-Power/Mod
meter.
(h) Verify oscilloscope waveform's modulation
envelope is the intended modulation depth.
(i) Set
KEYING
switch A4S1 (A5S1) to
ON
.
(j)
SET THRSH
lamp A10DS1 shall be flashing on
and off.
(k) Simultaneously
monitor
oscilloscope
waveform's modulation envelope (when
modulation is present) and
SET THRSH
lamp,
while decreasing the modulation depth. Adjust
TONE LEVEL
potentiometer A4A2R19
(A5A2R19) until
SET THRSH
lamp just turns
full on or the mod depth is less than the fault
threshold determined in step (b).
(l) Set
KEYING
switch A4S1 (A5S1) to
OFF
.
(m) Oscilloscope waveform's modulation envelope
should be the modulation depth for the
modulation depth fault threshold determined in
step (b).
