User's Manual

Model 1150A DVOR
9-18 Rev. - November, 2008
This document contains proprietary information and such information may not be disclosed
to others for any purposes without written permission from SELEX Sistemi Integrati Inc.
9.7.12.3 Sideband Generator Phasing
This procedure is performed to align sidebands 1 and 2 to the same phase with each other. A preliminary adjustment
check is made at the Sideband Generator. This adjustment is then checked using the Carrier antenna.
a. Perform the procedure in paragraph 6.4.16.
b. Install 5 watt dummy loads to sidebands 3 and 4 at the transmitter. Install a 180° cable in-line with
sideband 1 (ensure that the 180° line section is phased for the station frequency).
c. Disconnect carrier feed to the carrier antenna and terminate with at least a 100 watt load. Connect the
carrier antenna feed cable to the monitor input.
d. Set TX1 DC INPUT (BATTERY) and TX2 INPUT (BATTERY) circuit breakers to the ON position.
e. Set TX1 AC INPUT (LINE) and TX2 AC INPUT (LINE) circuit breakers to the ON position.
f. Connect oscilloscope to 1A4A4. Adjust oscilloscope so that a waveform fills about 3/4 of the screen with a
ground reference at the bottom of the grid. Refer to Figure 9-8. In order to do this alignment adjust the time
base on the oscilloscope so individual sawtooth waveforms can be viewed.
g. Select Transmitters>>Configuration>>Offsets and Scale Factors screen. Add or subtract degrees to Tx #1
Sideband 1-2 Phase Offset until all nulls of the sawtooth are at ground or as close as possible to ground.
Once this is done the waveform should look like an even band across the grid. If some of the nulls are
excessively out of phase with the others (nulls are far from reaching ground); the antennas corresponding to
these nulls are out of phase with the other sideband antennas with respect to the carrier antenna. Refer to
1150DVOR Antenna Operations and Maintenance Manual to check phase length of antenna feed cables.
h. Click on the Transmitter 2 ON button.
i. Select Transmitters>>Configuration>>Offsets and Scale Factors screen. Add or subtract degrees to Tx #2
Sideband 1-2 Phase Offset until all nulls of the sawtooth are at ground or as close as possible to ground.
Once this is done the waveform should look like an even band across the grid.
j. Click on the Transmitter 2 OFF button to shut off the transmitter. Remove 180° line section from sideband
1.
k. Install 5 watt dummy loads to sidebands 1 and 2 at the commutator input. Reconnect sidebands 3 and 4, and
install 180° line section in sideband 3. Click on the Transmitter 1 ANTENNA Button to restart Transmitter
No. 1 as the on-air transmitter.
l. Adjust oscilloscope so that a waveform fills about 3/4 of the screen with a ground reference at the bottom
of the grid. Refer to Figure 9-8. In order to do this alignment adjust the time base on the oscilloscope so
individual sawtooth waveforms can be viewed.
m. Select Transmitters>>Configuration>>Offsets and Scale Factors screen. Add or subtract degrees to Tx #1
Sideband 3-4 Phase Offset until all nulls of the sawtooth are at ground or as close as possible to ground.
Once this is done the waveform should look like a nice even band across the grid. If some of the nulls are
excessively out of phase with the others (nulls are far from reaching ground); the antennas corresponding to
these nulls are out of phase with the other sideband antennas with respect to the carrier antenna.
n. Click on the Transmitter 2 ON button.
o. Select Transmitters>>Configuration>>Offsets and Scale Factors screen. Add or subtract degrees to Tx #2
Sideband 3-4 Phase Offset until all nulls of the sawtooth are at ground or as close as possible to ground.
Once this is done the waveform should look like an even band across the grid.
p. Click on the Transmitter 1 OFF button. Remove all loads and 180° line section. Reconnect all cables to
their respective antennas.