490S-1 HF antenna tuning unit (United States), AVIONIC COMMUNICATIONS SYSTEMS


The Collins 490S-1 antenna tuning unit is an HF antenna coupler which automatically 
matches the impedance of aircraft shunt or notch antennas to a 50 ohm transmission line. 
It operates in single- and dual-ARINC configurations throughout the entire 2 to 30 MHz HF band. 
Operating efficiency is claimed to range from 70 to 95 per cent, depending upon antenna impedance. 
The system can automatically tune to a voltage standing-wave ratio limit of 1.3:1 across 
the entire HF band within an average time of 4 seconds and a maximum time of 7 seconds. 
It operates satisfactorily on all types of modulation at 400 W maximum average RF input or 1,000 W PEP. 
The 490S-1 is designed to operate ideally in an ARINC dual-system installation to eliminate 
the possibility that a single fault would disable both systems. In order that the system may be 
located as closely as possible to the antenna itself, it has been designed and constructed 
to withstand the severe temperature and vibration environment associated with the tail/stabiliser 
area of the aircraft. The MTBF rating is in excess of 5,000 hours, the operation being constantly 
self-monitored. The system is contained in a pressurised casing which is internally divided into 
the control and RF sections. These are separated by a thermal shield. No cooling air supply, 
either blown or external, is required. The electronic elements feature the use of planar cards 
fabricated from multilayer copper and glass-epoxy materials which provide high rigidity. 
The control circuits mounted on the cards consist mainly of integrated

Specifications 
Dimensions: 190 x 127 x 400 mm Weight: 7.5 kg Power supply: 115 V AC, 400 HZ 
Temperature range: -54 to +71ºC Altitude: up to 50,000 ft