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1.1 TECHNICAL DESCRIPTION
The 1.2M VSAT Antenna System is an elevation over azimuth positioner featuring the simple, rugged Roto-Lok
drive system for the azimuth which produces very low backlash, high stiffness and high reliability and driven by a
low backlash, gear box with a DC motor. The elevation system features a highly reliable linear actuator to control
elevation. All drive components are high strength steel, housed in lubricated for life housings which results in the
most reliable, no maintenance system with the minimum of weight. The reflector is a offset, prime focus, aluminum
illuminated by a corrugated horn. The RF power amplifier may be installed on the feed boom, or inside the truck. A
Handcrank across AZ axis is included allowing easy antenna positioning if the controller malfunction and elevation
actuator my be driven with a battery charger or other 12 volt system. The basic 2-port antenna system weighs
only 150 pounds.
RF SYSTEMS
The offset reflector/feed system produces co-polarization patterns that easily meet the 29-25 log theta requirement.
The .8 f/d optics reduces off axis cross-pol in the asymmetrical plane. The RF power amplifier may be installed on
the feed boom, or inside the truck. Waveguide that run to power amp across each axis can be via twist-flex or
rotary joints. The system can be configured for either 2-port or 4-port
The patented Roto-Lok drive system utilizes highly reliable aircraft control cables in a redundant configuration to
achieve a zero backlash, light weight, very stiff drive system. It achieves this high tech performance using low
tech components by simply wrapping the cable around the driver capstan several times before wrapping the larger
driven drum. The method used to wrap the capstan results a minimum free length of cable. The load in the cable
on the main drum is exponentially reduced as it is wrapped around the drum. Therefore the total elongation of the
cable when under load is minimized. The Roto-Lok system results in stiffness of up to 10 times that of comparable
gear or harmonic drive systems. The cables are pretensioned and spring loaded at the main drum attachment
point which eliminates backlash at installation and from any unexpected cable stretch in the future.
ROTO-LOK DRIVE SYSTEM
The Az Roto-Lok drive system is driven by a low backlash worm gear set with a 40:1 ratio. The factory low back
lash of the worm gear set is reduced further by the Roto-Lok drive ratio resulting in a lash equivalent to only .06 dB
as seen by the RF system. The gear sets are housed in a sealed housing which allows the gear set to be
continuously lubricated in synthetic oil which maximizes gear efficiency and minimizes wear.
SECONDARY DRIVE SYSTEM
Light weight, reliable, servo quality DC motor with integral gear box is used for the Az drive. This motor was
selected because it provides the best torque to weight ratio as well as allowing dual speed operation for slewing
and peaking. These motors produce constant torque over the speed range with no cogging at low speeds which
ensures smooth operation when peaking the antenna. The 24V DC design provides current limiting torque control
and will allow vehicle battery operation if necessary. A linear actuator is used in the elevation drive, a low cost
alternative to a typical roto-lok system. This system offers dependable and continuous constant torque over the full
travel motion of the elevation axis.
MOTOR DRIVES
SECTION 1- OVERVIEW
