F. HI -FIX 



1. GENERAL 



The Hi -Fix system was developed by the Decca Navigator Company, 

 Ltd., as a high -precision, lightweight, portable, position -fixing system A-*-' It is 

 a single -user system designed for hydrographic, geophysical, and other survey- 

 ing and tracking operations where an accuracy of a few feet is required at ranges 

 as great as 100 nautical miles. 



Hi -Fix is a phase -difference system and may be operated in either 

 the hyperbolic mode, which requires three transmitting stations ashore (master 

 and two slaves), or in the ranging mode, which uses two slave transmitters 

 ashore and a master timing oscillator and transmitter aboard the navigating 

 vessel . Time -multiplexing is used on a common carrier frequency of about 

 2 mc . The slave stations may operate unattended in the Hi -Fix system . 



The position is displayed to the navigator in digital format on two 

 counters . Supplementary display and automatic plotting equipment is available . 



2. DESCRIPTION 



This system utilizes closely synchronized, phase stable, cw frequency 

 transmission from the master and the two slave stations. Each station trans- 

 mits sequentially on the same frequency; the timing is controlled by the master 

 oscillator and other associated circuitry. As illustrated in Figure VI -4, the 

 slave 1 and slave 2 transmissions are keyed by the master trigger signal with 

 a 0.3 and 0.6 second delay, respectively. Using a time -sharing system and a 

 common frequency of operation makes it a simple matter to change the frequency 

 of the Hi -Fix chain. Five operating frequencies are available, and a frequency 

 selection is made by the operator at the master station. 



a . Transmitter Unit 



The master oscillator unit provides the drive signal for the master 

 transmitter . At the slave stations the controlling receiver provides the input 

 for the slave station transmitter, which is identical to the master station trans- 

 mitter. The transmitters are portable, are rated at 25 watts, and are gener- 

 ally located close to the antenna. The antenna is a guyed portable mast ap- 

 proximately 30 feet in height. A ground plane is generally required for each 

 shore station antenna to obtain stable and reliable transmission to ranges beyond 

 line of sight . 



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