136 BELL SYSTEM TECHNICAL JOURNAL 



end. This falling off occurs largely in the get-away loss at the trans- 

 mitting end of the radio circuit, as the diagram indicates. 



Fig. 8 depicts an all-radio system provided with intermediate 

 repeaters and compares for illustration purposes the transmission 

 levels obtaining therein with those for a wire system. The solid 

 lines are for radio and the dash for wire. It will be seen that the 

 radio system courses thru wide transmission level variations as com- 

 pared to the ordinary wire system due to the large attenuations 

 obtaining and particularly to the large step-off loss near the sending 

 station. 



The figure illustrates the same spacing for both radio and wire 

 repeating and gives a measure of the difference in amplification 

 required in the two cases. Altho in the radio repeaters the level 

 can be permitted to drop to low values, nevertheless a large part of 

 the total amplification has to be supplied at relatively high power 

 levels and it is this fact, together with the antenna structures required 

 at each point to "get into" the ether transmission medium anew, 

 that militates against the economics of radio repeaters as compared 

 with straight-away radio transmission. The tendency will be to 

 "stretch out" the straight-away transmission due to the fact that 

 for the longer distances the transmission loss increases relatively 

 slowly. While we may look for some important uses of radio re- 

 peaters in special cases, we should not, in general, expect them to be 

 as important to the radio art as are wire repeaters in wire operation. 



Transmission of Side Band Without Carrier 



In dealing with the subject of power levels in radio transmission, 

 it is important to recognize that a modulated radio telephone wave 

 consists of two components, one, the carrier frequency itself and the 

 other, the so-called side bands, which are the actual modulated 

 components. This resolution of the modulated carrier into two 

 or, rather, three components, the carrier and two side-bands, has 

 been given mathematically a number of times and need not be re- 

 peated. It is physically analogous to the resolution of the uni- 

 directional current of a microphone transmitter into direct current 

 and alternating current components, the direct current corresponding 

 to the carrier and the alternating current to the modulated components. 



Now, the important thing about this matter of side bands and the 

 unmodulated carrier component, with reference to transmission 

 considerations, is this, that it is the side bands alone, and not the 

 carrier, which convey the actual intelligence. The function of the 



