At present, 100-kw transmitters are being used. The radiated power 

 is dependent upon the antenna . Low antenna efficiency and lack of antenna gain 

 at these frequencies permits use of only 2-3 lew of radiated power. Useful 

 coverage of the area can be obtained at radiated power levels of about 2-10 kw. 

 Automatic control at the antenna maintains the constant radiated wave phase 

 characteristics required. 



The system is designed as a hyperbolic network but may be used in 

 the range-range mode. When operated in this mode a highly precise frequency 

 standard must be carried aboard the navigating vessel but the system can estab- 

 lish a fix by receiving signals from only two shore stations. 



Three types of receiving antenna are being used. A 35 -foot whip is 

 the most efficient unit for surface vessels. A 10- or 12-foot probe may also be 

 used and can be mounted either vertically or horizontally as space permits . 

 The same antenna coupler is used interchangeably. A loop antenna is used 

 aboard submarines and requires a loop coupler. 



The present Omega receivers indicate two phase-difference readings. 

 Each reading is shown by two dial indications, one being the cycle (or lane) 

 count from to 99 cycles and the other the percent phase difference per cycle 

 (100% = 360°). A strip-chart recorder is also provided to trace the two phase 

 differences (neglecting the cycle count). Remote indication can also be provided, 



The time differences as measured by the receiver are manually 

 plotted on specially prepared charts . To plot a position to an accuracy of 

 2-6 nautical miles, the navigator must be able to plot to an accuracy of between 

 0.03 and 0.1° latitude. Allowances for diurnal and seasonal phase shift, taken 

 from tables or charts, must be made by the operator before an accurate plot 

 can be made . 



Computers to utilize the required information and automatically track 

 and plot a vessel's position in geographic coordinates are not yet available, but 

 are in the early development stage . Such computers appear to be particularly 

 necessary for use aboard high-speed aircraft, which cross one lane (7.9 

 nautical miles) in a very short time. 



Equipment to resolve the problem of ambiguities of lane identification 

 is not available with the early developmental Omega equipment. Other available 

 navigation aids and dead-reckoning procedures must be used. The strip-chart 

 recorder at the receiver helps to correct lane counts that have been lost and 

 permits rapid recognition of anomalous propagation which might go unnoticed 

 on a counter-type display. 



81 



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