. Principles of radio transmission and reception with antenna and coil aerials . Fig. 9.—Dependence of received current on number of turns However Rc increases somewhat faster than proportional to Nas AT is increased, because of the proximity of the added turns,and hence / decreases somewhat as N increases instead of beingstrictly constant. Rx is likely to be large compared with RG when N is very small,and hence for small N, the variation of J with N will be a straightline, as shown in Fig. 9. As AT increases, Rc becomes large com-pared to Rx and the tendency of / to increase with N is reverse
. Principles of radio transmission and reception with antenna and coil aerials . Fig. 9.—Dependence of received current on number of turns However Rc increases somewhat faster than proportional to Nas AT is increased, because of the proximity of the added turns,and hence / decreases somewhat as N increases instead of beingstrictly constant. Rx is likely to be large compared with RG when N is very small,and hence for small N, the variation of J with N will be a straightline, as shown in Fig. 9. As AT increases, Rc becomes large com-pared to Rx and the tendency of / to increase with N is a result the curve of / has a maximum. The value of N atthis point may be called the optimum number of turns. Itsvalue will be greater the greater the external resistance. DeMnger) Principles of Radio Aerials 473 (b) Varying X with N and a constant. When Rx is large com-pared to Rc and does not vary appreciably with wave length Joe This variation is shown in Fig. 10. When Rc is large comparedto Rx, however, since Rc cc —t=-, roughly,. Fig. io.—Dependence of received current on wave length when external resistance is large However the effect of the adjacent turns increases Rc faster thanstated, as X is diminished, and hence I tends to approach a con-stant value for short wave lengths, as shown in Fig. n. Theseconclusions may, however, be vitiated by the variation of Rxwith X. (c) Varying a, with N and X constant. When Rx is largecompared to Re, I oca2 This is shown in Fig, 12. When Rc is large compared to RIfsince Rcoca, /oca, 474 Scientific Papers of the Bureau of Standards wa. 15
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