EXTENSION OF THE TELEPHONE SYSTEM TO SUITS 



169 



curves show up rather slrikirrgly I ho fad th.it Ihe transmission to the 

 south is much poorer than that to the northeast of Deal Beach. This 

 result agrees with experience since greater difficulty is usually en- 

 countered in communicating with a vessel when the line of trans- 

 mission is along the coast than when it is straight out to sea. The 

 larger transmission loss may be due to shore absorption or, possibly, 

 to refraction of waves by the electrical discontinuity represented by 

 the coast line. This high attenuation effect was observed rather 

 uniformly in all of the measurements, and would itself form an inter- 

 esting subject of investigation, using more absolute methods of 

 measurement. 



Fig. 17 shows the circuit-equivalent-distance characteristic for 

 the off-shore course taken by the vessel. The curve is. generally 

 similar to that for the near-in course. 



TRANSMISSION TEST 

 BEACH and S.S. Bloucc 

 July 20, 1921 



jlBBOUND ON CouASt 3 



Channel I Receiver 



<S 15 



Diiumi from Deal Beach to Ship 



Fig. 17 



The rate at which the transmission of the circuit varies with change 

 in distance is an important matter in operation, since it determines 

 the frequency with which the amplification in the circuit must be 

 readjusted to keep the equivalent constant. In accordance with 

 the Austin-Cohen formula, the equivalent should vary at the rate of 

 about 0.25 units per statute mile (1.6 km.) with the vessel 100 miles 

 (160 km.) out, assuming a square law detector. In the worst case 

 found, the circuit equivalent varied at the rate of 0.5 unit per statute 



