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BELL SYSTEM TECHNICAL JOURNAL 



Zg-jZji. If Z^ is a pure resistance the sending-end impedance is a 

 pure resistance. Hence a quarter wave-length line may be used to 

 connect two circuits of different impedances and these impedances may 

 be matched by controlling the value of Zg either by varying the diam- 

 eter of the conductors or their spacing. Likewise, if Z,, is fixed and Z^ 

 is made very small, then Zg will be extremely large. 



60 CYCLE 

 SOURCE 



RADIO 

 TRANSMITTER 



Fig. 4 — ^Antenna sleet-melting circuit. 



In Fig. 4 two units of the type shown in Fig. 3 are excited through 

 transmission lines 1 and 2 of equal length in order to give the correct 

 phase relations in the radiating elements. The lines are joined in 

 parallel by condensers of low impedance at radio frequencies and they 

 are connected in series for 60-cycle currents by the quarter wave-length 

 line A which, being short-circuited at the one end, presents a very high 

 impedance to radio frequency currents at the other end and therefore 

 behaves like an anti-resonant circuit. The quarter wave-length line B 

 serves as a transformer and is adjusted to match the impedance at the 

 junction of lines 1 and 2 with that of the radio transmitter. The 

 quarter wave-length line C is effectively short-circuited for radio fre- 

 quencies by the condenser D and acts the same as A. These quarter 



