The Challis messenger. (Challis, Idaho) 1912-current, 1924-04-30
Super-Heterodyne
Aid In World War
Invented by American Army
Ofcers-Two Impor-
tant Parts.

There are five fundamental meth
DDS used 10 obtain louder signals I:
~ Regeneration (2) Super-regen-
GRAFTON; 80 Radio frequency ampli-
hcation; "a Audio frequency am
piifcation; (5) Super-heterodyne.
The limitations Of each scheme are
as follows. ~ Regenerative cir
cults, when permitted to oscillate, act
as small transmitters and create inter-
ference for nearby receiving sets; (2)
Super-regeneration is not selective and
1t is difficult to control; (3) Untr1ed
radio frequency application by
means OF transformer coupling does
not do justice to all wave lengths and
tuned radio frequency amplifcatiop
requires too many adjustments to
tune the various circuits; "a Audio
amplifcation is limited to two stages;
90 The super-heterodyne is free from
the limitations possessed by other
methods Of simplifying. but is complex
in construction. The super-heterodyne
Is sensitive to weak impulses. 1t is
a sharp tuner, but not critical. 1t is
easy TO operate, as it has only two
controls.
A super-heterodyne consists chiefly
Of TWO parts, frequency changer and
a iong wave receiving set 1t is based
on this reasoning: A radio frequency
emplifer will operate easily on long
wave lengths. but not so on short
wave lengths. 1t was imperative dur
ing the World war to devise method
capable Of picking up feeble short
wave signals used by the Germans in
trench, submarine and other commu-
nicatiOn systems. Thus the super !
heterodyne was invented by Maj. E. |
H Armstrong while in France. He |
studied the problem and decided to /
receive the short waves and then /
change them TO long waves, making /
II possible TO use efficient Iong-wave
radio frequency amplifers-
The wave changer can be built In
an entirely separate unit and be as
distinct from the ordinary receiving
set as an audio amplifer unit A wave
changer consists of a detector tube
having two frequencies supplied to il;
the frequency OF the incoming signal
picked up by the antenna and second,
a frequency furnished by a vacuum
tube oscillator, called the "hetero-
dyne," which feeds the detector by
means of a suitable coupling. The
output of the frequency changer has
a frequency equal to the difference
between the signal frequency and the
frequency Of the keterodyne oscillator.
This difference can be varied by adj
iusting the heterodyne frequency.
For example if an incoming signal
has a wave length OF 400 meters or
80 kilocyc1es and the heterodyne tube
Is adjusted TO oscillate at $50 kilo-
cycles, the difference between the two
will be 100 kilocycles-
The heterodyne could be adjusted to J
)scillate at $50 kilocycles and the diff
ference would still be 100 kilocycles.
t makes little difference which way
I is adjusted The difference in the
frequency amplifer. The
can be controlled by
wo adjustments, one for the wave
ength of the incoming signal and the
'ther to control the frequency Of the
scillator tube One is called the
vave-length control and the other the
changer.
The super-heterodyne is designed TO
vercome all difficulties of radio fire.
uency application at short,wave
angths- II converts the frequency OF
he incoming signal to value that !.
an be amplified without difficulty.
To operate a super-heterodyne the
Ignal is tuned in just as with any
set The incoming signal IL
hen mixed with signal coming from :
be local oscillator tube or heterdyne
he result is a signal of much lower
equivalent to a high wave
myth This low frequency signal Is L
assed through an intermediate IRE >
uency amplifier designed especially
n long-wave ampliication. The sig
nj is then passed on to the loud "
1eaker and audio frequency ampli- o
pr OF phones
Each stage of anlplihcation is shield III
|. preferably in metal compart- ct
ent. II is not necessary TO have OF
,p on the compartment. All grid l.
ads must be as short as possible.
I "