EXTENSION OF THE TELEPHONE SYSTEM TO SHIPS 163 



necessary large amplification is supplied at both ends of the radio 

 link, partly in the transmitting station wh?re the voice currents are 

 amplified up to power proportions and partly at the receiving end where 

 the amplification is likewise large altho at small power. In the radio 

 telephone circuits which were operated in the experimental work 

 the power in the sending antenna to that in the receiving antenna 

 is in the ratio of roughly 10 10 . This requires amplification which 

 was distributed somewhere near equally between the sending and 

 the receiving ends. It has been found convenient to express such 

 transmission losses in terms of a power ratio using 10 0,1 as a unit. 3 

 Thus the above antenna to antenna power ratio would correspond to 

 100 of such units. 



Circuit Transmission Equivalents 



It is necessary that the amplification of such a circuit be sufficient 



to offset very closely the loss, in order that the net loss be small. 



Actually, in the tests, the radio portion of the circuit was worked 



with a net transmission loss of about six units, meaning that at least 



95 per cent, of the radio over-all circuit losses were wiped out. This 



means that if a change of say 10 per cent, occurs in the amplification, 



or in the ether loss as by fading or movement of the vessel, the circuit 



equivalent will be greatly affected — changed by about 200 per cent. 



The difficulty of maintaining the ship circuit stable will therefore be 



appreciated. 



Fig. 12 shows the transmission loss (of six units) obtained for the 



radio link during the tests and also the other losses which are in the 



wire portion of the combination system. The distribution of losses 



in the first circuit will be noted to be approximately as follows: 



6 units in the radio link. 



3 units in the hybrid coil — balancing network. 



12 units in the wire circuit to New York. 



6 units from the New York central office to the subscriber. 



3 The unit used in this paper is one which has been found convenient in which 

 expressing the transmission loss or gain of a circuit. One unit is taken as that power 

 ratio which is equal to 10° - 1 . Thus, if the attenuation or amplification of a circuit 

 is one unit the power at the two ends are in ratio of 10° - 1 ; if ten units, in the ratio of 

 Kpxo-i or JO; twenty units would therefore have a power ratio of 100, and so on. 

 The "advantage of using a power ratio instead of a current ratio is that it is unde- 

 pendent cf the impedances of the two portions of the circuit considered. The ad- 

 vantage of expressing the power ratio as an exponent is that on account of the ex- 

 ponential nature of attenuation it enables the net transmission efficiency of a system 

 to be readily derived by algebraically summing up the individual losses and gains. 

 This unit has been selected as more suitable for general use in expressing trans- 

 mission efficiencies than the 800 cycle "mile of standard cable" which has sometimes 

 been made. The ratio between these two units is as follows: 1 mile of standard cable 



P 1 



equals 0.95 units as used in this paper. -=p =10 01 = t—-z e 'o-io9> units. 



J 2 U.7J 



