RADIOBEACON TRANSMITTER
ND500II (125 WATTS) DOUBLE SIDEBAND - NO VOICE
Page 5-7
15 September 2003
(p)
Oscilloscope waveform shall be similar to the
unmodulated RF output waveform depicted in
example 'N' of figure 6-1. The peak-to-peak
voltage of the waveform shall be between 10.0
and 14.0 volts for operation between 190 and
650 kHz or between 8.7 and 12.7 volts for
operation above 650 kHz.
(q)
Disconnect oscilloscope from
RF MON
connector J1.
5.3.6
MODULATION DEPTH CHECKS
:
Verify the tone oscillator and modulation circuits are
operating within their required limits and the
modulation envelope is the desired depth (maximum
of 100 percent), as follows:
(a)
Verify the requirements of paragraphs 5.3.2
through 5.3.5 are completed and the RF output
(forward power) has been set to 125 watts.
(b)
Set or verify
MOD %
potentiometer A4R2 is set
fully counter clockwise.
(c)
Set
VOLUME
potentiometer R1 fully counter
clockwise (turned off).
(d)
Set all switches to positions tabulated for
Calibration Setting
in table 4-1.
(e)
Connect an oscilloscope, using a suitable
coaxial cable, to
RF MON
connector J1.
(f)
Oscilloscope waveform shall be similar to the
unmodulated RF output waveform depicted in
example 'N' of figure 6-1.
(g)
Set
MOD
switch S2 to
ON
.
(h)
Simultaneously monitor oscilloscope waveform
and slowly adjust
MOD %
potentiometer A4R2
clockwise until the modulation depth is 100
percent.
(i)
Modulation depth shall linearly increase, from
near zero percent to 100 percent, as
MOD %
potentiometer A4R2 is adjusted from its fully
counter clockwise setting.
(j)
Oscilloscope indication shall be similar to the
tone modulated RF output waveform depicted
in example 'M' of figure 6-1. The modulation
envelope shall be free from clipping and shall
not be distorted.
(k)
Adjust
MOD %
potentiometer A4R2 clockwise
for a modulation depth of 95 percent, as
indicated by oscilloscope waveform.
(l)
Set
TEST
switch S6 to
DC CURRENT
.
(m) Indication on lower scale of
TEST
meter M1
shall be between 45 and 65 (4.5 and 6.5
'Amps') for operation between 190 and 650 kHz
or between 40 and 55 (4.0 and 5.5 ‘Amps’) for
operation above 650 kHz.
(n)
Set
TEST
switch S6 to
B+ VOLTS
.
(o)
Indication on
TEST
meter M1's lower scale
should be between 40 and 52 volts.
(p)
Set
TEST
switch S6 to
MOD % REF
.
(q)
Adjust
SET 100% REF
potentiometer R2 for a
'
Mod %
' indication of 100, on lower scale of
TEST
meter M1.
(r)
Set
TEST
switch S6 to
MOD % READ
.
(s)
'
Mod %
' indication, on lower scale of
TEST
meter M1, shall be between 91 and 99.
(t)
Connect an oscilloscope between A11TB1-14
and A11TB1-15.
(u)
Oscilloscope waveform shall be a sine wave,
with a peak-to-peak voltage that is between 3.0
and 5.0 volts.
(v)
Disconnect oscilloscope and connect a
frequency counter between A11TB1-14 and
A11TB1-15.
(w)
Frequency counter's indication shall be within
five percent of pre-selected tone frequency
(400Hz or 1020Hz).
(x)
Disconnect frequency counter from A11TB1-14
and A11TB1-15.
