Vector-LP Radio Beacon Transmitter Technical Instruction Manual
Page
4-9
Section 4 Testing and Adjustment
Issue 1.1
(b) On the RF synthesizer PWB(s),
change the carrier frequency using
BCD switches S1 through S5. Each
switch represents one of the five most
significant digits in the carrier
frequency expressed in kHz:
- S1 is thousands digit (
x1000
)
- S2 is hundreds digit (
x100
)
- S3 is tens digit (
x10
)
- S4 is units digit (
x1
)
- S5 is the tenths digit (
x0.1
)
(c) Perform RF drive symmetry testing
and adjustment procedures (see
4.3.6.9).
(d) Change the RF filter tap settings (see
4.3.6.2).
(e) Calibrate the transmitter’s output
power (see 4.3.6.3).
4.3.6.2 CHANGING RF FILTER TAP
SETTINGS
For a frequency change, change the tap
settings on the RF filter PWB as follows:
NOTE
If your frequency is changing between the
standard frequency band (190 - 535 kHz)
and the extended frequency band (535 –
1800 kHz), you will need to change the RF
filter PWB (A14). Contact Nautel.
(a) Turn off the RF power and the ac and
dc circuit breakers.
(b) Remove the rear cover from the
transmitter to gain access to the RF
filter PWB (A14).
(c) Enter the frequency into Table 2-7a
(standard frequencies) or 2-7b (high
frequencies, VR125 only) to determine
the tap settings for the six jumpers.
Connect the jumpers to the appropriate
taps.
(d) Turn on the ac and dc circuit breakers.
(e) Install the rear cover on the transmitter
and perform the calibration in 4.3.6.3.
4.3.6.3 CALIBRATING TRANSMITTER
OUTPUT POWER
Calibrate the transmitter’s forward power
and related parameters as follows:
(a) Select reflected power to be monitored
on the exciter/control assembly’s front
panel analog meter (see 3.6.8.2).
(b) Select side A in the Changeover
Control menu. Go to the Power Module
menu.
(c) Monitor TP17 of interphase PDM driver
PWB A (A6) with an oscilloscope.
(d) Set the RF output to 0 W by pressing
the
Power Increase
and
Power
Decrease
buttons at the same time.
(e) Press
RF On
. Ensure all side A RF
power module fans turn on (VR250
only). Set modulation to 0%.
(f) While monitoring the PA voltage for the
side A RF power module (see
3.6.13.2), slowly increase the RF
output power until the PA voltage is
65 V. Stop increasing power if at any
time:
x
the PA voltage between RF power
modules varies by more than 5%, or
x
the reflected power on the analog
meter increases above 10 W
(g) Use an external current probe to verify
that the output power is 100
r
20 W.
(h) Increase power until you reach the full
rated or maximum level, whichever is
lower. Use an external current probe
and the following formula to determine
the output power:
Power = Current
2
x R
load
