Crystal Radio:
An Historical Survey
An Honors Thesis (ID 499)
by
Christine D. Craddock
Thesis Director
~ 1(
(.,
'- ;;t;;::
------------------~--~-~------Ball State University
Muncie, Indiana
"arch 24, 1987
Expected date of graduation -- May 1987
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-
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TABLE OF CONTENTS
INTRODUCT ION
•
THE CRYSTAL RADIO
•
•
•
•
•
1
•
4
•
HISTOR I CAL DEVELOPI"IENT
.
•
7
•
CONCLUSION •
13
B IBL IOGRAPHY
•
•
14
Books •
•
•
14
Articl.s •
GovernMent
-
•
Pub. ie.tiona
.
•
15
•
•
17
LIST OF" FI6lRES
-
1.
Da~.d
2.
UndaMped Waves
•
•
2
3.
Crystal Radio In Sch. . .tic
•
4
4.
Oscillation and Rectified Oscillation
Wav• • •
•
•
•
•
•
•
2
6
-
CRYSTAL RADIO.
~1:.n!M..BA~!.2
AN HISTORICAL SURVEY
is a n... gi ven to on.. of th.. ..ar I i est
for . . of radio receivers known to science.
It co.e. frOM the
sa.. era a. the original ·spark-gapM radio tran.mitter -- the
age of Heinrich H..rtz, GuglielMO Marconi, and Nikola T... la.
In a short ti ... it grew to know a widespread popularity, both
in the hOMe and in the lAboratory, and then finally it was
overwhelMed by the technological r ..volution of World War II.
Today it has becoa. an archival relic, obsolete in its
siMplicity, known only a. a children'. toy if it is known at
all.
In the beginning, all radio operated on th.. principle of
MRllt!::me..!MHlY!ni£!! (NO broadcasting.
Nt broadcasting is
the process of varying the aMPlitude of a radio-frequency
wave to reproduce .aund.
Thi. proc .... was once further
divided into two broad catagories.
The early spark-gap
tran_issions w.re known as vi.uuu-1t.ltilr-hv, because they
were created with a telegraph key.
The waveforM so produced
consisted of groups of oscil'ations repeated at regular
intervals, with the AMplitude of the oscillations within .ach
group decrea.ing continuously.
-
called
~OY ... ,
Th.... tranSMissions were
and they produce-d in the re-c.i ver
telegraphic dots and dashes of a single audio tone.
A later
2
radio,
H
was then cAli ed
~i rt!U!Ltelm-hgo~,
frOM its use of a
telephone-type Microphone to iMPose chAnges in aMp I i tude on a
continuous osci Ilation.
an outline or
This produced YlUilMRtS;L!tAXU. with
which varied according to the waveforM
~~t!2R~
of the sound waves or speech patterns entering the
Microphone.
Both vire ..... telegraphy and wireless telephony
variations in the aMplitude of an oscillation.
,.
r"
r
n
J~
"fv
J
'"
Figure 21
UndaMped Waves
Crystal radio was invented while the world was still
u.ing wireless tel"graphy exclusively, but it was later
-
discovered that it would receive either form of AM
3
trans.i.sion.
The r.ception of an
~
broadcast involv••
three funda.ental step. -- 1) a. the radio w.ve p ••••• the
a.rial, the oscillation MUst b. transf.rred to the wire of
the receiving circuit. 2) the tliU!:nninL!altLut so produced
in the circuit MUst b.
that it
~~t!!1~.
bec~s dtr~1-~Yr.r:.ent
or half of it removed. so
pul •••• and 3) the direct
current puls.s MUst be .ad. to produc. audible sound.
A
MOdern electronic receiver viii -.plify the voltage in the
circuit at
SOM.
ti •• during this process, to incr.ase its
capabi Ii ty to produce sound.
The crystal receiver. on the
other hand, depends on the pow.r of the tranSMitting .tation
to provide sufficient energy to produce the sound.
This is
the . .Jor r.ason crystal radio ha. such a li.ited rang. of
reception.
It ts also for this reason that the crystal
receiver i . unique aMOng radios of every era.
~
broadca.ting was a .ilestone in the history of
COMMUnication.
"any .en labored long years to bring radio to
the forefront of an unprepared world.
Fro. a scientific
curiosity it beca•• a .eans to bring people together, and to
bridge oceans, MOUntains, and those parts of the world that
lay as y.t un.xplored.
The history of the crystal receiver
is concurrent with the history of radio it.elf. of the first
great COMMUnication between peopl. sinc. the invention of the
telegraph.
FrOM its beginning. to the age of the technology
that was to cast it a.ide, her. then is the story of crystal
-
radio.
4
In its siMPle.t fora a crystal receiver is cOMposed of
four parts -- th .. Mria! or antenna .s it is now called, the
~!.2IiH....LtC~i vi.!HLur.s.Y!1
containing inductance and
capacitance which are both variable, the
which acts as •
dt!.~t2!:.'
~ts1!~tD~~~1A!
and the MtHlRb2Dt!! which r..,roduce
th .. radio broadcast in audible sound.
In a MOre cOMplex for.
of crystal receiver the.e •••e cOMponents MAY be elaborated
on and the size of the circuit incr ..ased, but th .. ir
individual functions reMain the SAMe.
illustrated in
~igur ..
Figure 31
The
A~i.§!
The basic circuit i .
3.
Crystal Radio In Sch. . .tic
absorbs the incident radio wave. frOM a
transMittinv station, thereby ... tting up electric
oscillations in the wire.
The wave energy captured by the
rec .. ivi,ng aerial is partly diSSipated a. heat in the aerial
itself and in the ground connection, and partly transferred
-
to the rest of th .. receiving circuit.
In the crystal
receiver, where there is no a.plifying force to suppleaent
5
-
the energy of the radio wave., the capability of the aerial
to absorb the wave energy and transfer it to the rest of the
g~.
the
aerial beCOMe. the driving ca.ponent of the circuit.
To
circuit beCOMe. critical.
Tovether with the
capitalize on its function. the Ca.MOn crystal receiver
aerial t. a long wire strung either vertically or
horizontally.
The MOst efficient form of aerial has a length
of one-half the de.ired wavelength of reception.
Once the wave energy pas.es through the aeria'. it
enters the S I ~~t.KJti:ii.nL.9.!£Y1!. or
associated
~AI.iAb..!t_C~~t2[.,
ltmILUrcy!!.
i.!:!iL~!m_~U
and
which i . now referred to as a
It function. as a
t.~9D'-!t-1Yni.ng
cOMponent.
deter.i.ning the radio frequency or frequencies to be
received.
Oscillations of Many frequencies enter the aerial.
The tuning circuit provide. aaximua voltage to the rest of
the reeei ver wh..,. the inca.ing frequency is its t..t!l!Slft-tlMl1
!~~.
By adjusting the inductance and capacitance of
the circuit, its resonAnt frequency can be varied to
correspond with a set of desired radio frequencies.
This
tune. the receiver circuit to different broadcasts.
Without
this cOMponent, the crystal receiver always responds to the
stronge.t radio signal entering the aerial, as it will
provide the greate.t voltage.
The current in the receiver at this point is still AC or
§llCI.uUtUI-S.YI.rmi.
MUst be
.r.Ktlfi~
To produce sound in the headphones it
or converted to
II1r~-sYr.t.m!.
(DC).
large nuMber of naturally occurring .ineral. rectify
A
6
altern.ting curr.nt at v.ry low voltages such •• those
produced in a crystal receiver.
The efficiency of the.e
r.ctifying .inerals d.cr ••••• proportionally.s the voltag.
incre.ses.
The.e .in.rals are all poor conductors, and . r .
MOstly ••tallic oxide. or sulphides .ueh as galena (PbS),
iron pyrite
(FeS~),
chalcopyrite
(Cu~SFe~S~),
MOlybdenit. (MoS), and copp.r pyrite
(FeCuS~).
zincite (ZnO),
In light
contact with a ..eta I wire called a "cat's whistcer," or in
SOM. cases with the pressure contact of a scr.w, a rectifying
crystal .erve. as a
~~~
in the receiving circuit.
Although it has b.en rectified, the signal retains its
out I ine or envelope which was forMed in the i.age of the
sound patterns b.ing trans.itted.
Becau•• the env.'ope of an
oscillation is identical in both directions, none of the
out I in. has been lost by .liMinating on. direction.
way the· original progra. .ing
i~osed
on the oscillation has
b ••n transf.rred froa AC'to DC, which will
lat.r produc.
sound.
Figure 41
-
In this
Oscillation and Rectified Oscillation
7
The sound is
produc~
in . .gnetic headphone. by
activating And deactivating the e.ectroaagnet.
There have
been MOre MOdern for.s of headphone• • ince the Magnetic type
wAS
invented, but it still works the be.t for cry.tal
receivers becau.e of it. high
iMp~ence.
Low resistance
headphones are not suitable for crystal radio work due to the
high re.istance of the detector, which .ay be .everal
thousand ohMs.
Headphone. for such use should have an
iMPedence nearly equal to that of the detector.
Ordinary
Magnetic headphone. frOM 1,000 to 2,500 ohMS illPedence in
each side can be efficiently u.ed.
The headphone. and the
detector are connected with each other in .eries, and then
together in parallel across the tuning circuit for .aximu.
efficiency.
The crystal radio ca.e in when ·wirele•• • wa. bright and
exciting, and
.tay~
in World War II.
through the darkne•• of Hitler's Europe
It. technical siMplicity wa. behind both
it. ti.ele•• popularity and it. bru.que de.ise.
While now
thought of MOstly a. a toy, it has .een action in all walks
of life.
Even today, if it serves no other purpo.e, an
understanding of the technology of crystal radio iaparts an
understanding of the fund . .ental. of AM radio reception.
During the developMent of radio apparatus in the late
1890's and early 1900'., the U. S. Patent Office was kept
8
busy with inventors prot.cting th.ir finds.
In the fi.ld of
radio det.ctors were such na. . . as S. W. Pickard, General
H. H. C. Dunwoody, and 8. W. Pi.rc..
Exp.ria.ntal radio
stations were just beginning, as Heinrich Hertz had only
conducted hi. experi . .nts on electrOMagnetic wav •• in the
early 1890's, and Nikola Tesla worked on his spark-gap
.xperiMent. in the latt.r part of the . . . . decade.
In the ear I y 1900' s, magaz i ne. such •• §£Lent Uts.
~!~4D
were beginning to explore the science of "wireless
telegraphy."
Radio was still very MUch a scientist.' fi.ld.
Another decade would pa.s before the ca..on Man would enter
the field of crystal radio construction, and begin to listen
to the apark-gap trans.issions around hiM.
FrOM the
itY!1.tt i:.n of the U. S. Bureau of Standards in 1908 ca... the
first real analysiS of ucontact rectifi.rs· in terMS of
H.rtz'. electrOMagnetic waves.
The old theory of
ther.a41'lectric curr.nt action, appl icable to the known
sciences (since Hertzian wave. were still very new), was
difficult to av.rcOIM even through the next dIKade.
It would
be as late a. World War II before the flow of scientific
change would begin to MOve a. fast as it is seen to MOve
today.
The 1910'., while in
SOMe
respects still reluctant to
shake away the old science, forged ahead bravely into the new
realM of "wireless u cOMMInication.
§s.i..tn...tUis_Am~ti~
published. lengthy treati.e in 1910 on the construction of a
crystal radio capable of receiving a five-kilowatt
9
broadcaster over a di.tance of 500 .ile..
Today.any
stations broadcast with ten tiMes this MUch power.
De-1ln.~'
in its
D~artaent
Tht
For Juniors, carried a column
frOM "The Junior Wirele.s Club Of AMerica," now -- under
an~h.r
n . . . -- the olde.t radio club still in existence in
the nation.
Overseas, the "Physical Society Of London" was
examining contact rectifiers and "electrotherMal u phenOMena.
Although their theory was wrong, they still .ade a valuable
contribution in their app.ndix to the article, in which they
elabor.ted on the use of such a device as a
~@!t~tgc.
~@di~l~eRb
A later article compared detector types and rated
their sensitivity.
Back in the State. again, the fi.,d of industrial
education was
b~inning
to pick up what would be a great
MOveraent in the 1920's -- the teaching of radio reception in
industrial arts classes.
SUrprisingly, it would be found in
cla••es fro. such diverse are.s as electricity, metal
working, and even wood working.
Newspapers and fa.ily
magazine. were bevinning to cover the topic that would becoa.
a
hous~old
project in the next decade.
And at this . . . .
ti . . , the U. S. Navy was using the first docwaented
19u9~n
crysta' receiver, a 'and.ark not only for being the first,
but also siMply for being documented.
Recorded evidence of
crystal radios actually being used for .ongwave reception is
spar.e at be.t, de.pite dOCUMentation of it. theory_
-
The Roaring 20'. were truly the decade of crystal radio
in the hoae.
IbLbltel:.At.X-Di.sUtJll led the way with a detai led
10
radio department in every issue, covering events at hoae and
around the world.
si~'e
The fads were to see how smail and/or
a radio could be . .de and .till have any kind of
reception range.
Contests were run, prizes offered, and
every newspaper and Magazine large enough to afford it
entered the game.
It was a -boys' technologyU now, having
co.e around the circle frOM a highly controversial scientific
experiMent.
Now the latest designs were COMing frOM the
dining roo. table.
Or~e
young man designed a set in a billfold, consisting
of thr ..e induction coils with a capacitor, and a crystal -ail constructed whil. recovering in bed from a long illness.
A young Man of twenty-one captured another contest by
designing the whole radio on and around a cardboard corn . . . 1
box.
SoMe little time later,
bi!t~~~Di~~l
reported the
first publicized incident of two girls building a receiver
they had copied the corn .eat box design frOM the former
issue -refUSing all help from father and brother. M But the
smallesit radio actually designed in the 1920's MUst have been
Alfred Rin&hart's ring radio.
It contained only a crystal
and single coil, with the crystal and coil taps (by which its
inductance could be varied) mounted on top of the coil it.elf
which was worn around the finger like a ring.
Using only an
umbrella for an aerial, it received WJZ in Newark, NJ, frOM
Elizabeth,
~,
SOMe five or ten aile. away.
By the 1930's, industrial education wa. already looking
back at the crystal receiver as a Mproject for the younger
11
boy,- in favor of the vacuum tube technology.
The whol.
world was very MUch taken with the vaCUUM tube -- the faMily
aagazine. w.r. quick to drop the crystal radio fad in favor
of this new technology.
Science MAgazine. still carried the
old t.:hnology to SOMe degr.e, but it was clear the fad had
gone as quickly as it had ca.e
80.e
that radio itself was forgotten.
ten y.ars before.
Not
Th. dining rOOM table was
still occupied, only now it was covered with tubes and
batteri...
T.I.vision was in it. first exp.riMental stage.,
Made possible by the advent of the vaCUUM tube.
The science
of ·wireless COMMUnication- was beginning to MOve faster now,
and new ideas w.re taken up and as quickly cast aside as
another ca.e along.
It was the beginning of a whole new
world.
World War II in Europe began in the lat. 1930's.
As
Hitl.r MOved •••• ingly unch.cked across the land, the
.'I-but-forgotten ·children's toy· ca.e back to the p.ople
again.
They n.ed.d an .asily hidden, e.sily asseMbI.d,
no-powe-r radio receiver that coul d be Made cheap' y out of
hou.~old
parts, and the crystal radio served th . . w.ll.
Th.
Dutch lMderground had a preference for putting them in
t.'ephones and hanging BOut of Order- signs ov.r th •• for the
Nazis.
They lifted the receiver to hear the radio broadcasts
fro. Atlied nations and Und.rground trans.itters.
Th. French
Underground sent to the BBC in London for crystal radio
sch . . . tics using loop aeria's.
It i. unfortunate that the
BBC no longer has records of the specific scheaatics.
And in
12
what •• y have been the radio's MOst iMportant application,
prisoners in POW caMps and soldiers in foxhole. Made
receivers with a razor blade and pencil
lead for a detector.
In the U. S., perhaps fueled by warti . . rationing and
civilian preparations for potential e.ergencie., crystal
radio reappeared in two places.
Articles about emergency
radio receivers began to appear, with crystal radios figuring
prOMinently.
And on the lighter .ide, popular Magazines
began to design crystal
r~ios
in tin cans for boy. on
bicycles. usinv the bicycle fra. . as a ground.
diode, today
consider~
!~
The gerManiUM
crystal detector, was a product
of warti.e technology and not released to the public until
well after the height of the fad had passed.
While the Allied world was fighting the war, Ecuador,
South A.erica, who had not yet chosen sides, was building it.
very first radio station.
In the 1940's, HCJB, "The Voice of
the And ..... built and distributed quantities of crystal
radios to the Indi.ns in the MOUntain regions of the country
who had no access to COMMercial .et..
As it happened, a
great nuMber of Ecuadorian residents had no COMMercial .ets.
and this fact was prOMptly Made known to HCJB.
ready country for this inexpensive syste..
Ecuador was a
Through the
technology of crystal radio, HCJB spread the gospel of Jesus
Christ over aile. of "unreachable- terrain.
Kanya
MOre-iMpressive technology can boast a I ••s-honored lineag.
than the siaple crystal receiver.
13
With the relea.e of World War II's solid state
technology, the crystal radio was
history.
relegat~
to the annal. of
There was a minor wave of revival during the 1970's
when the .elf-sufficiency and environ.entalist Move.ents
began, but neither it nor they gained .uch momentuM.
After a
certain lap•• of ti.e, it takes a great deal of energy to
search out the uncataloged technology of another era, and
that is what crystal radio is.
Without the COMplete
knowledge of the 1920's dining roOM hobbyist at hand, the
1970's dining roo. hobbyist never ca.e to be.
IDOved too far too fast.
There are few people today who would
go back to that technology if they could.
too perfect.
Technology has
Modern science is
The flaws of a previous era, exciting and
cha"Mlging then, have becoae too inconvenient to the modern
hobbyist.
SOMeday, if there is a need, the crystal radio May rise
again like a phoenix fro. the ash.s of MOdern technology.
But if there is no need, MOdern Man will never willingly seek
out the -hotae-brew" technology.
Perhaps it has yet to be
discovered that when the technology of the pioneers has been
forgotten for a long enough time, it becomes a pioneering
technology again.
Its use belongs once MOre to the
enterprising pione.r who wish •• to make a state.ent to the
-
rest of the world.
SUch now is the crystal radio.
14
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15
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II
~-1tH:.-!!t"btln!~L
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U
8Fig_L~.L
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16
HA Wirele••
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July 23, 1910, pp. 53-4,
Oct. 8, 1910, pp. 229-30, Oct. 15, 1910, pp. 246-7, Oct.
22, 1910, pp. 268-9.
Tel~raph
Sc;~ti.!!~_AIl!:tlL~§ygg~4l1l1L
Harvie, Bordon A.
"The Construction of a Crystal Detector
Receiving Set." IMutriaL6I:UJ!a..9.ni.!lh Aug. 1923,
pp. 316-17.
"How To ....ke a Loose Coupler."
1922, p. 28.
IIlLblt.~ut.X-DiJJuL.
Jun. 10,
Hug•• , F. Clarke.
"Crystal Radio -- A Project For the
Ycx.mger Boy." !wlY.atriA_'Educat~"A9AZi!ltL Oct. 1930,
pp. 138-9.
Junior Wireless Club of AMerica.
"How Boys CAn .... k. Their
Own Wireless." !he-Dt!i.n. .~ Aug. 1911, p. 134.
K~t.,
Charl.s.
~~!DtL
.1.....
"A Crystal R.ceiver."
Dec. 1923, p. 483.
l~tria_I_~t..
Keonnedy,
HAn Aaateur Wireless Set...
tIBsIniDtL Hay 1916, pp. 189-'92.
l~tri.AL&!:.t.
Kneltel, TOM.
-Radio Secret. of the ~rench Undervround.H
~ul ..r..J&W!YDic@!Loru!L Oct. 1985, pp. 17-19.
"A Crystal Receiver. H !D9YA~i.A_I_Arts~~
~UiOOJ!_'~dy£niot!.L Nov. 1948, pp. 373-5.
Kosloff, Albert.
"-cFareand, Anson.
"Build the
~1K-~"n!9n.L
Pfacf'ar I and, Anson.
Underground."
~oxho'.
....r.
Radio Receiver.H
1983, p. 23.
"Secret Radios of the WW II Dutch
eggyl aL~otImU-D~ni2Wb.. Nov. 1983,
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-Hore And tlGr. Indoor Aerials."
1922, p. 33.
-A Pocketbook Radio Set. II
1922, p. 29.
HRadio FrOM a Ring."
p. 32.
ThLLiteUr.x-Di.guh June 3,
IbLbll*ut.X-DiJilt.h Apr. 22,
ThLLiUt.§r~-D!..ge
__
HA SiMp' e VariOMeter R.cei ving Set."
June 3, 1922, p. 33.
-The SiMplest Crystal
pp. 426-7.
s.t.
H
h
June 3, 1922,
nULLi brArx-Di.guh
8t~~~-1~
Feb. 1925,
17
-The SiMplest Radio Receiver.1922, pp. 27-8.
-Wavelength-Frequency Chart. pp. 720-21.
!bt-bit~~D!~
BMl!.2-lLew~
Apr. 22,
June 1937,
t!gn_@!!!LURttuisn...of-AJiii!!IUt....HOIL-.Ad__-Bts,ei vi o.g
~.tL.ljC
gptfi~
Circular .120, U. S. Bureau of Standards, Apr.
24, 1922.
~~HL.~i~~LQHrnimL~~~~U~U~~~-Bectin~
~BllRmMl!.JfUtL~taL~~2U..
Ci rcul ar *121, U.
Bureau of Standards, July 17, 1922.
s.
!he1rJ.~!RL
___~tlx!WI-BAdi.Q.J;gMl!!Yn!~tl9!!L-~ed.!!.
Radi 0
PaMphlet .40, U. S. Bur.au of Standards
(for Signa' Corps, U. S. ArMY), 1922.
C(~ication
BAdio_{mltruftJlt!l____!L!k.ayL~..,t§.L CirculAr .74, U. S.
Bureau of Standards, Mar. 23, 1918.
§gyr.s.u-9L~.!!t!!taa~i.Q-Infor!Yt i2Dl-~tiI.L
Ci rcul ar
.122, U. S. Bureau of Standards, Sept. 12, 1923.
-