Vector-LP Radio Beacon Transmitter Technical Instruction Manual
Page
4-15
Section 4 Testing and Adjustment
Issue 1.1
4.3.6.13 ADJUSTING SPEAKER
VOLUME
See
Setting Protection Thresholds
(3.6.12.2). Adjust the Audio parameter as
desired.
4.3.6.14 READING MODULATION LEVEL
Read the modulation level as follows:
(a) Connect an oscilloscope to the
RF
MONITOR
connector (J8) on the
remote interface PWB (A3).
(b) Set the exciter in CW mode: use
and to scroll the display and set
Modulation to
OFF
using the
Toggle
switch.
(c) Adjust the oscilloscope’s timescale to
500
P
s per division (for 400 Hz
modulation). Adjust the amplitude
level of the oscilloscope to just cover
all eight divisions of the display with
the RF signal (see Figure 4-2).
Figure 4-2: CW signal set to fill display
(d) Adjust the position of the oscilloscope
signal so that the bottom of the CW
waveform is at the mid-point of the
display (see Figure 4-3).
Figure 4-3: CW signal with position
adjusted to mid-point of display
(e) Set the exciter in MCW mode: use
and to scroll the display and set
Modulation to
ON
and the Keyer to
OFF
using the
Toggle
switch.
(f) Measure the bottom of the waveform.
Each sub-division should correspond
to 5% in modulation. The bottom of
the waveform should be one sub-
division above the bottom of the
display when the modulation is at 95%
(see Figure 4-4).
NOTE
There may be some distortion in the
trough. This is an effect of class D
amplification called pinch off and can be
ignored as it does not produce significant
total harmonic distortion (THD).
Figure 4-4: MCW signal, 95% modulation
