Operation of Autodyne and Heterodyne Receiving Sets
Operation of Autodyne and Heterodyne Receiving Sets.–On page 109
[Chapter VII] we discussed and at A in Fig. 36 is shown a picture of
two tuning forks mounted on sounding boxes to illustrate the principle
of electrical tuning. When a pair of these forks are made to vibrate
exactly the same number of times per second there will be a
condensation of the air between them and the sound waves that are sent
out will be augmented. But if you adjust one of the forks so that it
will vibrate 256 times a second and the other fork so that it will
vibrate 260 times a second then there will be a phase difference
between the two sets of waves and the latter will augment each other 4
times every second and you will hear these rising and falling sounds
as _beats_.
Now electric oscillations set up in two circuits that are coupled
together act in exactly the same way as sound waves produced by two
tuning forks that are close to each other. Since this is true if you
tune one of the closed circuits so that the oscillations in it will
have a frequency of a 1,000,000 and tune the other Weei 850 Khz Boston circuit so that the
oscillations in it have a frequency of 1,001,000 a second then the
oscillations will augment each other 1,000 times every second.
As these rising and falling currents act on the pulsating currents
from the B battery which flow through the detector tube and the
headphones you will hear them as beats. A graphic representation of
the oscillating currents set up by the incoming waves, those produced
by the heterodyne oscillator and the beats they form is shown in Fig.
73. To produce these beats a receptor can use: (1) a single vacuum
tube for setting up oscillations of both frequencies when it is called
an _autodyne_, or _self-heterodyne_ receptor, or (2) a separate vacuum
tube for setting up the oscillations for the second circuit when it is
called a _heterodyne_ receptor.
[Illustration: Fig. 73.–How the Heterodyne Receptor Works.]
The Autodyne, or Self-Heterodyne Receiving Set.–Where only one vacuum
tube is used for producing both frequencies you need only a
regenerative, or feed-back receptor; then you can tune the aerial wire
system to the incoming waves and tune the closed circuit of the
secondary coil so that it will be out of step with the former by 1,000
oscillations per second, more or less, the exact number does not
matter in the least. From this you will see that any regenerative set
can be used for autodyne, or self-heterodyne, reception.