. The principles underlying radio communication . Pig. 197.—Double helix oscillation transformer; coils separated axially. cuited except when actually needed in order to keep the resist-ance of the antenna circuit low. ADJUSTMENTS OF TRANSMITTING SETS. 373 162. Direct Coupled Transmitting Set.—Direct instead of in-ductive coupling may be used between the closed circuit andthe antenna circuit, as in Fig. 200. (Direct coupling was ex-plained in Sec. 119.) One inductance coil is all that is the contacts shown, as much or as little of the inductance asdesired can be used in either circui
. The principles underlying radio communication . Pig. 197.—Double helix oscillation transformer; coils separated axially. cuited except when actually needed in order to keep the resist-ance of the antenna circuit low. ADJUSTMENTS OF TRANSMITTING SETS. 373 162. Direct Coupled Transmitting Set.—Direct instead of in-ductive coupling may be used between the closed circuit andthe antenna circuit, as in Fig. 200. (Direct coupling was ex-plained in Sec. 119.) One inductance coil is all that is the contacts shown, as much or as little of the inductance asdesired can be used in either circuit. In order to tune to somewave lengths it may be necessary to have an additional coil in. Fig. 198.—Hinged coil oscillation transformer. series in the closed circuit. By making the part of the in-ductance that is common to both circuits a small part of thetotal inductances in the circuits the coupling can be made asloose as desired. Since direct and inductive coupling arestrictly equivalent, the discussion of one applies to both. 163. Comparison of Coupled and Plain Antenna Sets.—In theplain antenna set of Fig. 194 the spark gap is in series with theantenna. Thus the resistance of the gap is present and helps to 374 TRANSMITTING APPARATUS. make the decrement of the radiated waves high. While highdecrement is an advantage In special cases, as explained inSection 160, it is usually not desirable. When the spark gapis in a separate circuit, coupled either inductively or directlyto the antenna, as in Figs. 195 or 200, the resistance of thespark gap does not enter into the antenna resistance. Theresistance of the gap is high, and can not be changed muchunder practical opera
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