. I principi alla base della comunicazione radio. L'interconnessione con la progettazione delle antenne a bobina è riportata in Bu-reau della Standards ScientificPaper No. 354 e in un documento di A. S. Blatterman, JournalFranklin Institute, volume 188,pagina 289, settembre 1919.alcune informazioni relative alla progettazione delle bobine per lunghezze d'onda corte sono fornite nel libro Wireless Experiments Manual, Di E. Bucher. Per comodità di costruzione, le bobine quadrate sono le più adatte. Il filo può essere avvolto in una spirale piatta (Fig. 178) o sulla superficie del telaio asquare (Fig.179). Con i flatspirals soltanto i fewturs sono u
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. The principles underlying radio communication . t inconnection with the design ofcoil antennas is given in Bu-reau of Standards ScientificPaper No. 354 and in a paperby A. S. Blatterman, JournalFranklin Institute, volume 188, page 289, September, 1919.Some information regardingthe design of coils for shortwave lengths is given in thebook Wireless ExperimentersManual, by E. E. Bucher. For convenience of construc-tion square coils are found to be the most suitable. The wire may bewound in a flatspiral (Fig. 178) oron the surface of asquare frame (Fig.179). With flatspirals only a fewturns are used, sincethe inner turns rapidly become less useful as the area dimin-ishes. The spiral type of coil is comparatively little used in theUnited States. The usual type of coil antenna consists of one or more turnsof wire wound on a square or rectangular frame. One or twoturns of copper wire wound on a simple wooden frame 3 or 4feet square will make a simple coil which will be suitable forsome purposes. For indoor use for all ordinary purposes the. TONLXTSTAG L OFAMPLIFIER FIG.I79A •SIMPLE.C01LANTE.NNA CIRCUIT. COIL ANTENNAS. 335 wire used for a coil antenna may be No. 20 or No. 22 ordinary-insulated copper wire, with solid conductor. The spacing of the turns of a coil depends on the allowablecapacity of the coil. Spacings of one-half inch and 1 inch arecommon; a spacing of one-quarter inch is also used sometimes. The capacity of a coil of given dimensions increases with thenumber of turns, at first rapidly, and then more slowly. Withthe wires close together, the capacity is a maximum and growsrapidly less when the wires are separated, until a certain criti-cal spacing is reached, beyond which the capacity changes veryslowly. For a square coil 8 feet on a side the wires should be placedat least 0.35 inch apart; for one 4 feet square, 0.2 inch; and fora 2-foot coil, one-eighth inch. Increasing the distance betweenthe wires decreases the inductance of the coil; at the same timeit
