Model 1278K Mobile VSAT Antenna System
15
Operation and Maintenance Manual
SECTION 5— FEED AND POLARIZATION POSITIONING SYSTEM
5.1 GENERAL
The Feed assembly consists of feed boom, upper and lower feed brackets, feed housing, RF components
and polarization drive housing. The pivot connection at the end of the feed is made with brash bushings. A
piece of 18" flex wave-guide is used at the end of the wave-guide tube to the OMT and connects to the
BUC. The chain drive assembly and 12V DC motor rotate the feed/OMT. Position feedback is from a 10-
turn potentiometer.
5.2 FEED
The feed assembly consists of an inclinometer, feed horn and OMT with male pivot bushings. The male
bushings pivot in delrin female bushings at each end of the OMT. These bushings are mounted to
mounting plate. The pol drive sprocket attaches to the OMT and the wave-guide attaches to other end
with M6 screws at the rear flange of the OMT. The feed/polarization drive is mounted underneath pol
mounting plate in feed box with gear on outside and driving pol sprocket to rotate feed.
5.3 POLARIZATION DRIVE
The feed/polarization drive is mounted underneath pol mounting plate in the pol drive box with a drive
sprocket mating to the motor shaft, which extends through the feed drive box. The polarization drive
motor) is a 12 VDC gear motor. Small gear is attached to the end of the motor shaft, that drives small gear
to drive the position potentiometer. The controller travel limits are +/- 95 degrees for a 2 port. See
TracStar Systems Controller Manual section 3.3).
If the chain becomes loose, re-tighten wire at chain joint. No maintenance of the polarization
motor/assembly is required.
The polarization drive is replaced by a complete unit including the motor, motor sprocket /gear, chain,
elevation inclinometer, potentiometer and gear, and drive sprocket.
5.4 POLARIZATION POSITION POTENTIOMETER
The polarization feedback is produced by a 10 turn, 1K-ohm potentiometer driven by the motor gear, and
mounted in the feed box and shaft extends outside the box. The resolution and accuracy is 0.3 degrees.
The potentiometer is rated for IP 65 environment, wind, rain, and dust, etc. The potentiometer is
mechanically set at the one-half travel position, ( 5 turns from either end) and will read approximately
500ohms at 0 degrees pol (stow). The potentiometer may be set using the controller the voltage reading
pol stow will read 2.5V at 0 degrees. See TracStar Systems Controller Operating Instructions included on
the accompanying disk.