The Morning Tulsa daily world. [volume] (Tulsa, Okla.) 1919-1927, 1922-07-25
Lesson No. 100.
The Effects of Frequency.

frequency Is a term applied to al
.orratlng current circuits referring
=. the changes in direction OF the
k.,.,ent. For example, lighting
.,-cui, which supplies 60 cycle cur
o., 20 a house is said to have a fire.
ano,cv of 60 cycles, while most OF
,ba spark signals heard on the re-
ceiyirg set have a frequency OF 500
cy,las. II they are from commercial
stations.
Tho frequency OF the current
rbich Is TO pass through the wind
,res u a transformer or other cleo
,ricql device having an iron core
,s an important consideration in de-
sienlng such equipment. An in
crease in the frequency usually
means a decrease in the dimensions
of the iron core used. II takes n
definite time to set up a given mag
retic field around n coil Of wire
and IN an iron core and II the cur
rex IS made TO reverse It's direction
T u11re often Il is necessary to re-
ducc the amount OF iron in the core
70 permit building up the field to
the same strength.
The lowest frequency employed
for commercial lighting circuits Is
q cycles which means so alterna-
tons Of current per second. This
frequency Is somewhat below the
range OF the usual voice or audlo-
freQuencies. When we get up into
the range Of radio frequencies the
current reverses extremely rapidly
40 that most of the apparatus Of
the sort mentioned above functions
without any iron core az all, having
so-called "air core" Examples OF
air-cOre transformers are vario-
couplers and receiving transformers
adio-frequency ampllfylnS trans
formers and oscillation transformers
~ various types for transmission
Purposes.
II is n peculiarly OF radio-fr
quency currents that they travel
chiefly on the surface OF the con-
ductor and do not penetrate deeply
into Il. This is the reason why tub
ing or strips of large area are en-
ployed in powerful transmitting
stations for those parts OF the cir
cults which carry high frequency
currents This also accounts for
the fact that a person coming in
contact with the antenna lead of
transmitting plant of moderate
power is not always severely burned.
Many OF the vaudeville acts are per-
formed with high frequency currents
jumping from the finger tips Of the
performers without injury.
A transformer designed 70 oper-
ate on say 500 cycles will probably
burn out IL subjected to the exces-
slve current which would be drawn
from n 25 cycle source unless a
large core suitable for the reduced
frequency was used. On the other
hand. a transformer designed for
so cycles may be employed on 100
cycles at slightly reduced power and
A. very low power on 500 cycles
without external choke coils.
Variations in frequency play ar
important part IN the reception by
radio of music or speech. Audio-
frequency amplifying transformers
usually function best at a certain
frequency, so that sounds at fire..
quencies above or below this are
not amplified in the Same proper.
ton. This Is the reason for the ap'
parent distortion in some types ot
reeiving sets employing severa
stages of audio-frequency ampllfl,
cation.
1t is the frequency OF an alter
mating current circuit<which makes
possible such apparatus MS th'
transformer. impedance coils, con