For slow-moving systems of 20 knots or less manual switching of 

 modulation frequencies controlled by the master is satisfactory, providing the 

 remote switching keeps in step with the master. At higher speeds it is neces- 

 sary for ambiguity resolution to be achieved on a continuous recording-chart 

 system where the switching processes are automatically controlled from the 

 master. Automatic timing permits the interrogation for ambiguity resolution 

 to be repeated at regular adjustable time intervals and is useful to speeds in 

 excess of 100 knots. 



Errors can be caused by ground reflections and are governed by the 

 modulation frequency, the antenna beam width, and the ground characteristics. 

 Broad beam antennas increase the severity of ground reflections. Errors intro- 

 duced by reflections at lower modulation frequencies will tend to be greater 

 under certain conditions of high reflection. 



Ground reflection effects can cause readings to deviate by an amount 

 which is a function of the excess length of the indirect ray, the strength of the 

 ground reflection, and most important, the relative phase of the microwave 

 carrier over the two paths. The effect is a swing or variation of readings about 

 the true reading, the amplitude of which is quite dependent upon the reflecting 

 properties of the surface. Antenna heights of the order of 200 feet or less help 

 reduce the swing error by reducing the grazing angle of propagated energy with 

 the surface of the terrain or water. 



4. SUMMARY 



a . Hydrodist MRB/2 



(1) Type of system: precision ship positioning and ranging. 



(2) Number of stations required for navigation: two remote 

 stations at either end of a base line. Two master sta- 

 tions placed side by side on the vessel, each of which 

 continually ranges on its own remote station. 



(3) Carrier band: 3 cm (2800 to 3200 mcps). 



(4) Minimal frequency difference of master stations: 80 mcps. 



(5) Length of base line: 10-20, 000 meters (nominal). 



(6) Radiated power: 100 mw. 



152 



arthur 31.1.ittlf,3nr. 



