Evening star., 1922-05-15
Expert Advice on Radio
No. How Radio Waves Garry Sounds.

vibrations of over 10000 second,
means must be devised for reducing
or cutting the waves down before
they can be transformed into sound
waves.
Detector Cuts Waves.
This Is done by means of an instru-
ment called g. detector. which cuts
the alternating currents in half by
acting like a valve which allows the
currents to flow in one direction but
not in the other. Hence the wire
less wave shown in figure would
appear as in figure s. after 1t had
passed through the detector and the
broken dot and dash wave. figure 2,
would be like figure 4. But as these
wireless electrical waves are never
audible they must be transformed
into sound waves in order to be
heard, and this Is done by an cleo
ktrical-mechanical device known as
the telephone receiver" Perhaps, at
first thought. it might seem possible
to connect an ordinary telephone
transmitter to a wireless telegraph
set and by talking into the instru
ment transmit the voice to person
at the receiving instrument. But
with. the old type radio telegraph
possible, for the sounds or words
would have been broken or inter-
rupted and would have been received
in fragments. In figure the sound
wave of word Is shown diagram
matically and such sound wave as
it would appear If carried by an in
terrupted wave Is shown in figure =.
Moreover, such waves as sent by
the old style spark-gap instrument
were not continuous. as they ap-
peared. but were composed or many
Independent or interrupted waves.
81, ino a.
phone was made possible by the dis
covery of means for sending unin-
terrupted or continuous waves. This
Is done by the audion bulb or vacuum
| tube, and it was this simple but won
derful instrument which brought
radio to its present state. SUCH a
continuous wave is represented by
figure Z, and when such a wave Is
varied OF affected by sound wave
| 1t Is made serrated or uneven, as In
| figure 8, but is not broken.
Therefore, such a wave, even when
transformed into sound waves and
| the original sounds exactly repro
duced.
Compared to PhonoEraph.
This may be clearer if we COM
| phonograph If the blank record
| with its spiral grooves Is placed on
| the recording machine the needle on
| the diaphragm will vibrate and cut
| little depressions in the wax as a
person speaks into the horn. Then.
| if the record is placed on an ordi-
! nary phonograph, the needle on the
| diaphragm follows these little depres-
| sions and causes the diaphragm to
| vibrate and reproduce the original
| sounds.
Therefore. we may compare the
radio waves TO the spiral grooves in
! the wax record and the variations
| upon them. caused by music or voices
| to the marks made by the needle.
And we may compare the receiving
| station to the other needle which
| transforms the indentations in the wax
| to sounds we can hear.
Hence it is no more correct to think
or speak of electrical or radio waves
being heard than to talk Of the inden-
| tations on a phonograph record being
heard, for just as the marks on the
| wax are made to create sound waves
| by mechanical means, SO the variations
| of a wireless wave may be made to
| create sound waves by electrical devices
| in the telephone receivers.
Copyright 1927
| (Tomorrow-How Detector Cuts Waves.)