The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1924-04-11
Super-Heterodyne
Aid In World War
Invented by American Army
Ohcers-Two Impor-
tant Parts.

There are five fundamental meth
DDS used 70 obtain louder signals;
ID Regeneration CD Super-regeI
GRAFTON; (3) Radio frequency amplt
fcation; Cd Audio frequency am
plitication; (5) Super-heterodyne.
The limitations of each scheme are
as follows: ID Regeneratiye cir
cults, when permitted TO oscillate, act
as small transmitters and create inter
ference for nearby receiving sets; CD
Super-regeneration is not selective anc
il is difficult TO control; 60 Untuned
radio frequency amplitication by
means OF transformer coupling does
not do justice to all wave lengths and
tuned radio frequency amplitication
requires too many adjustments to
tune the various circuits; (4) Audio
application is limited TO two stages !;
90 The super-heterodyne is free from
the limitations possessed by othei
methods of simplifying. but is complex
in construction The super-heterodyne
is sensitive TO weak impulses. 1t IL
a sharp tuner. but not critical. II L
easy TO operate, as ii has only two
controls.
A super-heterodyne consists chiefly
Of two parts, frequency changer ano
a long wave receiving set. II is basec
on this reasoning: A radio frequency
amplifier 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 Ii
trench, submarine and other commu,
nication systems. Thus the super.
heterodyne was invented by Maj. Z.
h. Armstrong while in France. He
studied the problem and decided to
receive the short waves and then
change them TO long waves. making
it possible to use efficient long-waye
radio frequency amplifiers.
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. wave
changer consists of a detector tube
having two freQuencies supplied TO 1t {;
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 heterodyne 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 OF
80 kiIocycles and the heterodyne tube
is adjusted to oscillate at $50 kilo
cycles, the difference between the two
frequencies will be 100 kilocycles
The heterodyne could be adjusted &c
oscillate at $50 kiLocycles and the diff
ference would still be 100 kilocycles.
Ii makes little difference which way
ii is adjusted The difference In the
two frequencies is impressed upon the
intermediate frequency amplifier. The
super-heterodyne can be controlled by
two adjustments, one for the wave
length of the incoming signal and the
other to control the frequency of the
oscilIator tube. One is called the
wsve-Iength control and the other the
frequency changer.
The super-heterodyne is designed to
overcome all difficulties of radio fire.
quency amplifcation at short-wave
lengths. 1t converts the frequency of
the incoming signal TO value that
can be amplified without difficulty.
To operate a super-heterodyne the
signal is tuned in just as with any
receiving set. The incoming signal Is
then mixed with a signal coming from
the local oscillator tube or heterdyne.
The result is a signal Of much lower
frequency equivalent to a high wave
length. This low frequency signal Is
passed through an intermediate fire.
quency ampIifier designed especially
for long-wave ampIifcation. The sig
nal is then passed on TO the loud
speaker and audio frequency ampli-
fer or phones.
Each stage of application is shield
ed. preferably In a metal compart-
ment. 1t is not necessary to have O
top on the compartment. All grid
leads must be as short as possible. !.