Evening star., 1922-07-03
BY A. HYATT VERRILIs
Expert ON Radio TechnoloGy.


Every user of RADIO receiving sets
knows something Of tuning and adjusts
his set to receive certain wave 1enkthss
yet few know how to adjust tfieif sSts
to the best advantage. Tuning 10 mefe-
ly altering the aerial length. so that It
vibrates to the greatest possible extent
to incoming radio waves Of defnite
length.
In order to understand this more
clearly, let US compare the aerial to q
weight suspended on a string, like q
pendulum. II this Is struck as 1t hangs
motionless the weight is driven TO ons
side. and then swings back. II the
stroke Is repeated as the, weight re-
gains its original position It will again,
the force exerted In striking It VIII be
lost overcoming the momentum Of the
swinging weight. II, on the other hand,
we wait until the weight has reached
the extreme limit of Its swing, q very
the opposite end of the, swing. BY thus
tapping the weight each time 1t reaches
the limit of its swing 1t may readily be
kept in full motion with very little
effort. ~
When the radio waves 90, out from
intervals of SO many waves per second:
This interval varies with the length oi
the waves. Thus a 3B0-meter wave IL
one sent out at the rate Of $50. .00C
strike your aerial $4,000 times each
second. but If the aerial Is not properly
adjusted or in resonance with the
waves it cannot vibrate to its greatest
capacity any more than the swinging
weight could travel through the ful
time. it travelled part way back. But
as the blows or waves striking the
aerial cannot be changed to suit ths
vibration Of the aerial the aerial mus
be changed to suit the impulses OF the
waves.
Varying the Circuit.
When this is done correctly. or the
aerial will vibrate to it's limit each
time the oscillations strike 1t. As J,
is Impractical to alter the aeria
Itself to accommodate 1t to dihefenl
waves, we provide means for varyine
its circuit. These may be plain ceii.
of wire. coils provided with sw1tcne'
and taps, coils with sliders, loose
coupled coils, vario couplers OF
variometers. No matter which form
of tuning device is used. the coil OF
inductance acts as part OF tne
aerial and by turning the movable
parts OF. the inductance or varying s
| the number Of turns on the col! W.
lengthen or shorten the aerial tc
meet the incoming waves and tc
vibrate to them to the best ad'
vantage.
II two or more metal plates are
placed close together. but not touch
ing. and are connected in the receiv'
ing set circuit we find that by NOV
ing one or more of these plates we
alter the wave length. Such devices
are known as variable condenser
and, while they are usually used II
connection with coils or other forms
of tuning Instruments, q set may bt
, perfectly tuned by means OF con-
densers alone.
No matter what form Of tuning de.
vice is used, there are certain thingi
to remember and certain ways Of
tuning which will make tuning
simpler than If you go about 1t blind.
ly and turn a knob here or a switcf
there by guesswork.
II the set you use ID single circai
Cube or crystal). tuning is simple.
If you are using q crystal set. AND
| the crystal has been tested by q bus
ger. the following is the procedure Il
follow:
Place crystal and cat whisker ii
contact and then vary the tuning de-
vice until signals are heard. Adjas
| the detector and tuner until the bes
results are obtained. OF course, Il
| the crystal has not been tested yot
| cannot be sure it Is in receptive Of
sensitive position, but II you have nj
buzzer tester you may test the crys
' tai by having some one turn an cleo