New-York tribune., 1922-07-23
This Is Title Bestowed on
Super-Heterodyne System
One Of +. II. Armstrong;
Epoch-Making Inventions
Valuable on Short Waves
Reproduces Radio Telephone
Speech Clearly Without
Distortion or Howling

called the Rolls Royce Of radio. Since
,ha, time have received such a num-
her Of inquiries regarding this system
that ! am going 70 give a brief out
line Of 10.
The super-regenerstive is one Of the
epoeh-making inventions Of radio and
was produced by Armstrong in 1919 It
,s undoubtedly the most sensitive re-
eeivor. as well as the most selective
known 10 the radio art. The principle
upon which 10 is based is that Of de-
.ecting a. one frequency and amplfy-
ing AZ another. The only drawback
20 II from the average radio fans
roint Of view Is the cost. as 10 en-
plovs from seven 20 nine vacuum
tubes: although there Is no tbcorctieal
limit 10 the number that can be used.
II was this system that enabled Paul
Cooley 20 successfully receive no less
than twenty-nine American amateur
stations az his temporary station in
Ardrossan. Scotland. 5000 miles away,
despite the fact that none Of the anna
teur stations was using more than one
kilowat Of energy for transmission.
Besides being extremely sensitive. the
super -heterodyns system also has an
important bearing upon the develop
mont Of the short wave ranges.
Important on Short Waves
Perhaps no better way Of expressing
this can be given than in the words
used In the letters patent granted 10
Armstrong on June 8, 1920, which are
as follows;
"The limit Of the practical ampiher
81 present is about 100 meters and the
range Of wave lengths from 70 100
meters are unused al the present time
because Of the difficulties Of amplify-
ing and detecting them. High fire.
euency amplifers have been con-
structed 20 operate on wave lengths as
low as 200 meters, but with only fair
efficiency.
"The present invention discloses a
method Of indirect amplifcation and
reception which operates independent
Of the frequency Of the incoming
oscillations and which therefore,
opens up the great range OF wave
lengths below 100 meters and makes
possible, in fact, the use Of waves Of
q few meters in length whereby radio
communication by directed beams Of
energy becomes practical PROPOSE
tion. The present invention may also
be used 20 great advantage on wave
lengths from 800 20 ! 900 meters with
a considerable gain in selectivity and
sensitiveness, as compared TO any
known methods"
How System Operates
A diagram showing the connections
for the super-heterodyne, using seven
vacuum tubes and one hcterodyne tube,
r. reproduced in the Radio Primer on
this page. The manner in which IL
operates is as follows. Assume that
We are listening for one Of the broad
casting stations operating on wave
length Of $50 meters. The frequency
Of this wave is determined by divid-
ing 300.0O0,O00 by the length Of IT,
which gives US approximately S33.33s
cycles per second. In other words
wave lengths Of 800 meters consist OF
alternating currents having a complete
change from positive 20 negative that
number Of times per second
Now IL is a well known fact that
amplifcation Of such high frequencie,
presents very serious difficulties. while
II Is much easier 20 amplify lower fire.
quoncies. The problem which the super
heterodyne principle solves. therefore
is one Of converting the frequency oi
tho incoming currents down 10 som,
predetermined lower frequency which
is much more readily amplifed.
The manner IN which this conver
sion is attained is by means Of the
heterodyne or beat principle: only
in the super-heterodyne principle the
beat frequency is adjusted 20 a point
above human hearing. Hcterodyne liz.
erally means "other power" and 10 is
the principle whereby a local source
Of power is employed In radio work
20 produce an audible frequency by
making the local power source clash
with the incoming currents az a pre-
determined number Of times per second
Describing the Heterodyne
This can be illustrated. for example
BY assuming that we are 20 receive
from transmitting station using con.
tnuous waves OF a wave length OF
5000 meters, or a frequency OF 10000
cycles per second. This, Of course, is
far above the hrman hearing. II We
connect IN small vacuum tube 81
that 10 acts as n transmitter, we car
cause 10 10 produce oscillations Of any
desired frequency by adjusting the
amount OF inductance and capacity In
the circuits about IL. Therefore, II ",
set this tube oscillsting az 60,50l
cycles per second. the wave IL pro
duces and the wave which is being re-
ceived on the aerial will be out Of
phase with each other 500 times pei
second. and the result is a note in the
telephone reeivers equivalent 10 th'
pitch caused By 500 vibrations pei
second.
Now there T. no reason why the fre
qucnoy resulting from this efec'
should be so low. Il can be made vel
above human hearing, and this is ex-
actly what is done in the super
heterodyne system. The incoming
oscillation and the oscillation pro
duced by the local heterodyne tube are
passed through the first detector. anc
converted 70 lower frequency. which
is transferred 90 the high frequency
amrlifer through the tuned circuit,
which are shown after the first de
tector tube.
Converted Current Amplihed
After the strength Of the converted
oscillations have been built up by the
high frequency ampliher. they arc
passed again through a transformer
and then rectifed by the second de-
t1ctor tube end passed through the
telephones, or carried on through two
stages Of audio frequency anplihea-
tion before being put through the
telephones.
There is no limit 20 the number Of
stages Of amplihcation that can be
used with this system. provided that
each intermediate stage Of high fire.
oueney smplifcaticn is az a lover fire.
ouency than the previous stage. and
that the conversion from one fire.
ouency 70 the other is made with the