66 



HYDROGRAPHIC MANUAL 



identification. If the lane count is lost it 

 is necessary to return to a known point and 

 reset the counters before continuing hydrog- 

 raphy. 



3-56 Corrections to Raydist measure- 

 ments. — As stated in 3-50 the R2 lane width 

 is assumed to be the same as that of the R^ 

 lane for drawing distance arcs from the 

 ground stations. The R2 distance and the 

 width of the Ro lane are complicated by 

 the fact that an elliptical method is used to 

 measure the sum of the R^ and R^ distances 

 and then the R^ distance is subtracted in 

 the phasemeter. The correction is a function 

 of the cycle differences in two signals, usu- 

 ally 400 cps. 



For example, if a frequency of 3280 KC 

 is used at the mobile transmitter, a fre- 

 quency of 1639.8 KC will be used at the Red 

 station distance measuring (C-W) trans- 

 mitter. The «i lane width will be 149.87307 

 feet, which is obtained by dividing 983,167,- 

 315 feet by 3280 and then dividing the re- 

 sulting wave length by 2. In this instance 

 the 



Rn distance in feet=149.87307i/'G-f 0.00012 

 {R1-R2) in which 



i/'G=Phasemeter reading for the R2 sta- 

 tion in lanes. 



i?i=Distance to Red station in feet. 



/?2=Distance to Green station in feet. 



The R2 distance in the sum of the R^ and 

 R2 distances is measured directly, but by 

 an effective frequency of 3280.400 KC which 

 is 400 cycles larger than the frequency 

 used to compute the lane width. The 3280 

 KC frequency from the mobile transmitter 

 is returned to the ship on a frequency of 

 3280.400 KC. The factor 0.00012 is the quo- 

 tient when 400is divided by 3,280,000. 



The above formula is difficult to use in 

 the field but it can be reduced to a formula 

 by which a correction to R2 distances can 

 be computed when the mobile station moves 

 from the point where the dials are set. The 

 correction formula is : 



R2 correction (in lanes) = +0.00012 

 [{^|,R"—^pR')— {xj,o"—xp'aU wherein the sub- 

 scripts R and G indicate Ri (Red) and R-. 



(Green) phasemeter dial readings respec- 

 tively and " and ' indicate readings at the 

 calibration point and the point for which 

 correction is desired, respectively. The for- 

 mula is used with the Rn lane width the same 

 as that of the Ri lane and no correction is 

 applied when the Ro dial is set at the calibra- 

 tion point. 



A second correction to R2 distances is 

 required if three antennas are used at the 

 Red station. If antennas are duplexed at the 

 Red station this correction is eliminated. 

 The arrangement of the three-antenna sys- 

 tem is described in 3-52. The correction to 

 R2 distances is related to the location of 

 the C-W (distance measuring) transmitter 

 with respect to the center of the antenna 

 system at the Red station. The correction 

 is expressed in the formula: 



Correction to R2 distance (in lanes) =d 

 cosine (A« — A,) in which d is the dis- 

 tance in lanes from the Red station center 

 to the C-W transmitter antenna. A, is the 

 azimuth of the mobile unit from the Red 

 station center, and A, is the azimuth of the 

 C-W transmitter antenna from the Red sta- 

 tion center (Fig. 18). 



The point of origin for measurement of 

 distances on a ship using three antennas is 

 related to antenna locations and may be 

 some distance from the location of the echo 

 sounder transducers, which, on most ships, 

 are located within a few frames of the fore- 

 mast. With the distance-measuring signal 

 antenna at the main mast and the receiving 

 antennas at the foremast, the point of origin 

 for the Ri distance is midway between the 

 masts (Fig. 19). The origin of the R2 dis- 

 tance cannot be defined as a single point 

 because of the elliptical configuration, but 

 for this computation is assumed to be at 

 the main mast. The Ri and R2 distances 

 may be reduced to the foremast by applying 

 a lane correction derived from the formulas : 



Ci=i/,D cosine {SH-Ar) 

 C2=YiD cosine (SH-Ar) — D cosine 

 (SH-Ag) 

 Where 



Ci==correction to Ri distances in lanes 

 C2=correction to R2 distances in lanes 



