The Washington times. [volume] (Washington [D.C.]) 1902-1939, 1924-08-04
.DISC0VERQUEER
KINKS IN RADIO
OUTFITS
Engineers Explain Why Sets
Act Funny on Different
Wave Lengths

Observant fans have noticed that
sets behave differently on long ana
short waves. some receivers acting
with greater efficiency on one or
the other. giving rise to many
puzzling questions as to why this
change occurs. When q set pro-
duces strong signals from KDKA
and fails to do 90 with stations
not 90 far sway, but on q higher
wavelenEth. or In the reverse con-
dillon. when IL brings In good vol.
uuae from WEAF and much less
from WOR, allowing Tor the DIFF.
ference In power and distance,
there must be something in the
set itself.
The fault in the set Il one OF
design. for the particular frequency
desired to be heard, rather than q
defect In any piece Of apparatus.
or an error In connections. When
engineers were less familiar with
the problems Of resonance at high
freQuencfes, they used to design
sets OF the universal type, having
wavelength range from 200 70
5000 meters.
Fruit Of Experience.
Experience showed them the err
roT OF continuing this practice, for
they Iound that on the lower waves
these sets were 1unctioning badly.
The presence Of Idle parts In the
circuit caused losses, because on
the short waves all the large coils
and condensers, while disconnected
were In close magnetic and capaci-
tive relation to the short wave
coils, causing great ABSORPTION. AS
q result Of this experience, the
designers changed the long and
short wave receivers into separate
units.
Receivers designed for broadcas,
reception, however, are not en-.
tirely free from the effects of idlc
parts. which accounts for the
losses occurring on different wave
lengths.
Cycles Of Current.
To explain more clearly the rea.
son for changing receiver design
for long and short waves. fhe
problem must be discussed n
terms Of frequency, or cycIea ~
current. The receiver mentioned
In the preceding paraeraph fsned
between a wavelength band OF 600
and 5000 meters. AZ 600 meter
the frequency is $1,000 cycles Der
second. and at 5000 meters It il
1VV,VVU cycles. With a tuning dif.
terence OF only 100000 cycles Il
was found advantageous to change
the design OF this receiver, max.
ING tWo distinct units. On the
broadcast tuning freQuencies 4
single unit tuner must include q
wave band between values an.
preaching zoo meters on one side
ana 900 meters ON the other. or The
ullaerene between 500. 900 cycles
ana 100000 cycles. witch Is the
frequency at 200 meters.
A Logical Conclusion.
In the first case. efficiency was
not expected on the 5000 meter rs.
ceiver on the lower waves. beca1Ise
OF the 100000 cycle tuning differ.
ence. It Is logical Conclusion
therefore, to state that no dcast
receiver can be efficient over s fra.
quency range two ana one.haIt
times greater. or 1000. 900 cycles g.
me solution Of the problem is in
the two unit system for broadcast
reception, one tuning below 36O
meters and the other above IL. a
slxty-five turn coil should be used
Tor the secondary Of the long wave
unit, tuning with eleven.plate cor.
densers Of .O0025 microfarads a..
pacity. The number OF turns -
the primary coils should Is ~.
duced or increased accordingly.