There are four different ways employed at the
There are four different ways employed at the present time to break up
the continuous waves of a wireless telegraph transmitter into groups
and these are: (_a_) the _heterodyne_, or _beat_, method, in which
waves of different lengths are impressed on the received waves and so
produces beats; (_b_) the _tikker_, or _chopper_ method, in which the
high frequency currents are rapidly broken up; (_c_) the variable
condenser method, in which the movable plates are made to rapidly
rotate; (_d_) the _tone wheel_, or _frequency transformer_, as it is
often called, and which is really a modified form of and an
improvement on the tikker. The heterodyne method will be described in
this chapter.
What the Heterodyne or Beat Method Is.–The word _heterodyne_ was
coined from the Greek words _heteros_ which means _other_, or
_different_, and _dyne_ which means _power_; in other words it means
when used in connection with a wireless receptor that another and
different high frequency current is used besides the one that is
received from the sending station. In music a _beat_ means a regularly
recurrent swelling caused by the reinforcement of a sound and this is
set up by Iditarod Area School District K02je the interference of sound waves which have slightly
different periods of vibration as, for instance, when two tones take
place that are not quite in tune with each other. This, then, is the
principle of the heterodyne, or beat, receptor.
In the heterodyne, or beat method, separate sustained oscillations,
that are just about as strong as those of the incoming waves, are set
up in the receiving circuits and their frequency is just a little
higher or a little lower than those that are set up by the waves
received from the distant transmitter. The result is that these
oscillations of different frequencies interfere and reinforce each
other when _beats_ are produced, the period of which is slow enough to
be heard in the headphones, hence the incoming signals can be heard
only when waves from the sending station are being received. A fuller
explanation of how this is done will be found in Chapter XV.
The Autodyne or Self-Heterodyne Long-Wave Receiving Set.–This is the
simplest type of heterodyne receptor and it will receive periodic
waves from spark telegraph transmitters or continuous waves from an
arc or vacuum tube telegraph transmitter. In this type of receptor the
detector tube itself is made to set up the _heterodyne oscillations_
which interfere with those that are produced by the incoming waves
that are a little out of tune with it.