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740
Radio Broadcast
J
I BAND TO I ' COVER '
r SPEECH "n
FREQUENCIES
FIG. 9
A curve showing the range of audible frequencies covered by the Hanscom coils
COIL WITHOUT — RESISTANCE
FIG. IO
Illustrates the difference between the Hanscom and other coils, the latter having the tendency to distort by reason of the side bands being chopped off
trols the feed mechanism various effects can be produced, but for average work a f of an inch spiral has been found satisfactory. This produces a coil which is -^ of an inch thick. In winding certain kinds of wire it was found advisable to use a roller with a spring tension against the outer edge of the coil as in Fig. 8. For the intermediate frequency circuit of the super-heterodyne, the writer has used two joils in series, each containing about one thousand turns of No. 36 wire with a .00025 mfd. condenser across the two coils. Various kinds of inductances can be wound on the machine, providing the hole at the end of the nozzle is large enough to permit the wire to run freely through it.
ADVANTAGES OF THESE COILS
THE greatest advantage of these coils is their small size. The magnetic field caused by the coil is naturally small and they
can be mounted without much fear of coupling effect with other parts of the apparatus.
In any form of radio inductance designed for reception of music and speech, it is necessary to cover a band of wavelength sufficient to avoid distortion of the voice or music. This is illustrated in Fig. 9 and in the coils designed by the writer this is obtained by the
FIG. I I
Shows a rear view of the winder. A wormdrive motor supplies the means for rotation
j
resistance in the coils which tends to broaden the tuning sufficiently as illustrated in Fig. 10. To those who are experimentally inclined, the construction of a coil winder as described will be diverting. The writer can assure those who attempt it that they will wind many coils and near coils before the results are entirely satisfactory. This is not said to discourage those who might desire to build it, but rather as a word of warning. Stick to it and it will work!
THE WINDING DATA FOR THE HANSCOM ' SUPER* COILS
INTERMEDIATE-FREQUENCY trans1 former — Primaries: — In the first stage, the primary coil consists of 500 turns of No. 36
FIG. 12
The nozzle and cam units are clearly shown. An oscillator coil is on the winding bushing