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RESEARCHES IN RADIO TELEPHONY
A THESIS
PRESENTED BY
ERWIN WALTER PETZING
TO THE
PRESIDENT AND FACULTY
OF
ARMOUR INSTITUTE OF TECHNOLOGY
FOR THE DEGREE OE
BACHELOR OF SCIENCE
ELECTRICAL ENGINEERING
MAY 29,19 19
APPROVED
CHICAGO, IL 646
Table o f C ont ent s
Oi Ct o i o c o o o 0 o o o o 0 o 5 o 3 0
C hapt er I
Keno tron
Chap t er I I
Us e as a Keno tronf or High
e Re c tific atiofl
Chap t er I
n strqc tion
C hap t e r I I
!ne Use Of a VT2
s
The Us e Of a VI
RESEARCHES I N RADI O TELEPHONY
Ob j e c t
In the las t few ye ar s the s tr i de s in
rad i o t e le phony have be en very rap i d . About
t en ye ars ago the s c i ent i f i c worl d was f i rs t
int ro duc e d t o the fac t that rad i o t e l e phony
wa s p o s sibl e ; but f or the f i rs t f ew ye ars f o l-
l ow ing,t he p r o r r e s s in th i s branc h was c om-
par ative ly s l ow due t o the d i f f i c ul t i e s in the
gene rat i on o f h igh frequency c urrent s o f the
undampe d wave type . The only two way s i t w a s
f ound po s s i bl e t o gene r ate c urrent s o f th i s
nature w a s by the arc gene rat o r or by the h i gh
frequency g enerat or ; but in the l as t s ix o r
s even years a — new type o f g enerat o r has c ome ih~
t o exis tenc e ; namely,
! The Ho t C atho de Vac uum
Tube !. Thi s generat o r prac t i c al ly revo lut i oni ze d
the ent i re f i e l d o f rad i o t e l e phony and t o a
l e s s e r ext ent rad i o t e l egraphy ; but had i t no t be en
f o r the war,i t i s rat he r doubt ful Whe ther our
advanc e r in th i s s c i enc e in the l a s t f our ye ar s
woul d hav e be en qu i t e a s rap i d as i t has be en .
The dif fimultie s enc ount ere d in rad i o
t e lep hony ar e s everal
l . The mo dul at i on o f l arhe amount s o f
2 . The mo dulat i on o f the s e c urrent s
w i thout d i s tor t i on .
3 . In c r e as ing the s e l e c t iv i ty t o suc h
an ext ent that in a c i ty o f a l arg e popul at i on
i t c oul d be us e d a s a means o f int er c ommunic ah
t i on j us t a s w ir e t e l e phony t o day .
use rs o f the s e t e l e phone s woul d no t have t o be
expe rt s t o ope rat e them af t er they are once in
ope rat io n
In the fo l l ow ing di s cus s i on the f i r s t two
o f the f our d i f f i c ul t i e s g iven w i l l b e c on s i d e re d ;
name ly,
1 . The mo dul at i on o f h igh amount s o f power
by the human vo i c e ; and
out d i s t or t i on.
As a pre l iminary t o the f ol l ow ing Art i c l e s
there are two rather int e re s t ing and ne c e s sary
sub j e c t s t o be d i s cus s ed
1 . The us e o f a thre e e l ement tube a s a
re c t i f i er .
the l o s s e s in the
tube by means o f a thre e e l ement tube us e d a s
a dynatron .
Thes e two ma tt er w i l l be t aken up in c hap t er s
I and I I .
c o o pe rat e d w i th me in s ome par t s o f the fo l l owing
inves t igat i ons .
Part I
C hap t e r I
The Deve l op ement and Us e of the Keno tron .
The deve l o pement o f the vacuum tube has
be en extreme ly rap i d in the l a s t f ew years and
w i th th i s dev el opement c ame a new typ e o f rad i o
frequency generat or ; name ly,the ho t c atho de
vacuum re c t i f i e r .
I t i s a wel l- e s t abl i sh e d f ac t that if a
heat ing e l ement i s enc l o s e d in a vacuum and
he at e d t o inc ande s c enc e that the re i s a the rm—
i oni c rad iat i on in al l d ire c t i ons . Th i s c an be,
and has be en de f ini t ely e s t abl i she d by putt ing
a pl at e around th e f i l ament and c onne c t ing th i s
in s e ri e s wi th a mi l l i amme te r and h igh vol tag e
bat t ery o f about 50 vo l t s t o the neg at ive s i de
o f th e batt e ry o r s ourc e o f supply wh i c h i s u s e d
f or heat ing the f i l ament t o inc ande s c enc e .
I t ha s be en f ound that th i s rad i at i on c on—
s i st s o f negat ive e l e c tr ons and that the number
o f e l e c tr ons emi t t e d inc rea s e s very fas t a s the
t emp erature o f the h o t c atho de inc re as e s unt i l a
po int o f s at urat i on i s re ache d . Th i s po int i s
d e te rm ine d by t he d imens i on s o f th e tub e .
I f the pl at e i s ke pt at a p o s i t ive p o tent i al
the se e le c trons emi t t e d w i l l be drawn t oward s
the pl at e and a current wi l l be s e t up in th i s
p lat e c i r c u i t . S e e f igure 2 . Th e c urrent in
th i s c i rcu i t w i l l be f ound t o vary as the vol t ag e
and c an be e xpre s s e d by the f o l l owing e quat i on
3_6 L §f
l l 4 . 6 5 ( 1 0 fe
Where
The c urrent in the p l ate c i rcu i t in
ampe re s .
I . § The l eng th o f the f i l ament in c ent ime t e r s .
r 3 The rad ius o f the c yl inde r .
Mr . Saul Dushman o f the Genera l E l e c tr i c C om—
pany f ound that the i oni c d i s c har ge from the ho t
c atho de inc re as e d from about . 1 4 amp ere p er s quare
c ent ime t e r at ab s o lut e t o . 3 6 amp e re s at
t o . 89 ampe re s at and t o ampe re s
at but at h igh t emperature s th e f i l ament
the e le c tron c urrent st re am . I f the charge in th e
s pac e surround ing the f i l ament be c ome s suf f i c i ent ly
gre at,no inc rea s e in t emperature at a g iven vol t age
w i l l pro duc e any furthe r c urrent . E i the r the pl at e
vo l t age mu st be incre as e d or the bul b c ons truc t i on
al t ere d s o a s t o d imin i sh the spac e charge . Br ing-
ing the p lat e and f i l ament c l o s e t o e ac h o the r w i l l
d imin i sh the S pac e c harge e f f e c t . The e f f e c t i s in
dicated at B in Fi, ur e 5 ; and f o r a~ low er app l i e d
pl at e vo l t ag e,at D wi th the dashe d l ine .
In the c ours e o f Dr . S . Dushman's inve s t iga—
t i ons , he s t at e s that the s afe cur r ent~ c ar rying
c apac i ty o f vac uum tube re c t i f i e r s,are a s fo l l ows
F or a f i l ament . 005 inche s c m . ! in d i ame t e r,
. 03 amp ere s c an s af e ly be emi t t e d pe r c ent ime t e r o f
l eng th and that unde r the se c ond i t i ons the f i l ament
he at ing current W1 1 1 repre sent wat t s o f p ower
p er c ent ime t e r o f l eng th. Fo r f i l ament s . 01 inche s
in di ame t e r cms . ! the s af e c urrent i s . 1 0
amp ere and t he p ower i s wat t s per un i t o f l ength .
Fr om th i s ,s ome ind i c at i on c an be go tt en o f what may
be exp e c t e d from tube s o f o rd inary d imens i ons ba se d
on the s e therm i on i c c urr ent s . Langmui r s t at e s that
the type o f tube d eve l o pe d by Dr . I rv ing Langmui r and
Dr . S aul Dushman,t oge ther wi th Wi l l i am C . Wh i t e o f
the Gene ral El e c tr i c C ompany has a c apac i ty o f 250
mi l l i ampere s and c an be us e d w i th vo l t age s as l ow
as 200 and a s h igh as vol t s . The e f f i c i ency
i s s t at e d a s F i gure 4 i s a d i agram o f th i s
bulb . I f a great e r c urrent than th i s i s t o be re c t-
ified,h e s t at e s i t is be t t er and more e ff i c i ent t o
c onne c t more bul b s in p ar al l el and pro bably ju s t a s
e c onomi c al as us in g a l arger bul b .
In c onne c t i on wi th the devel opement o f th e s e
tube s a cur i ous e f fe c t wa s enc ount ere d when the
j o int f i lament he at ing and the rmi oni c ( pur e e l e c tr on!
current s we re c omb ine d . In the f i l ament he at ing
cur cuit shown in F igure 5,th e c urrent c irc ul at e s
in the d i re c t i on ind i c at e d by th e do t t e d arrow s .
There f or e,unde r normal c ond i t i on s
,the amme t er s
Aland A
2read th e same . I f
,however
,the p l at e
c i rcu i t i s c l o s ed,and a current ind i c at e d by A
S
appe ar s in that c i rc ui t,i t s d ire c t i on o f f l ow
w i l l b e as ind i c at e d by the ful l l ine arrows . ( I sup-
po s e it i s unde rs t oo d that the d i re c t i on o f f l ow o f
th e current i s o pp o s i t e t o t hat o f the negat ive
e l e c t rons,in ac c o rdanc e Wi th the c ommonly ac c e pt-
e d c onvent i on ! . When th i s c urrent app ear s in AS
i t w i l l b e no t i c e d that the pl at e c urrent A3 wi l l
f l ow outward fr om b o th end s o f th e f i l ament . C on—
s e quent ly,at the l ow er end i t w i l l a s s i s t the
l ight ing current,
w h i l e at the t op i t w i l l opp o s e
i t . S o that , i f A i s the true l ight ing current,
the r e ad ing s o f the amme t ers wil l be g iven by
A 2 A A3 and A2 A A7
. Wi th smal l tube s,such
01
as use d f or re ceiv ing,th is e f f e c t i s o f no prac t i c al
imp ort anc e,but when larg er tube s pas s ing he avi er
pl at e current s ar e use d i t may be c ome s erious i f
the f i l ament i s al re ady worke d near the burn- out
Mr . Wi l l i am C . Whi t e,t o whom much o f the
re c ent devel opement s o f the Pl i o t ron i s due,ingen—
ious ly min imi ze d th i s e f f e c t by c onne c t ing that
part o f the c i r c ui t a s sh own in F igure 6 .
I t mus t be remembe re d that th i s ent i re d i s cu s s-
i on as sume s that the vacua in the s e tube s are pr ac t—
ic ally p erf e c t (wi th in a few t en mi l l i onth s part of
a mi l l ime t er o f mercury! and that the e l e c t ro de s and
wal l s o f th e tube have be en fre e d from any o c c lude d
gas s e s wh i l e th e tube wa s be ing e xhau s t e d . Th i s is
a c ond i t i on that i s hard t o o bt a in and hard t o ma in-
t a in,c ons e quent ly s l i ght var i at i ons w i l l o c cur in
the re sul t s obt a ine d by d i f f erent bul bs . A ful l d i s
cus sion on thrs subj e c t c an be o bta ine d by c onsul t ing
Dr . Langmuir' s paper app e ar ing in the Se pt embe r i s sue
o f th e ! Pro c ee d ing s 05 The In st i tut e o f Rad i o Eng i-
ne er s f or
Al t ernat in g c urrent re c t i f i e r s,manufac tur e d by
f or h igh and low vol t ag e s . The l ow vol tag e bul bs,
s ol d unde r the name o f Tungar re c t i f i er s,are c on—
struc t e d for vo l tage s up t o about 1 50 vo l t s and th e
Keno t ron f or vo l tage s from 1 50 t o vo l t s .
RESEARCHES I N RADIO TELEPHONY
Part I
C hapt er I I
The Us e o f a VT2
as a Keno tr on f or Hi gh Vol t age
Re c t i f i c at i on
The VT as th i s bul b i s c al l e d by the S i gnal2 ,
C orp s,i s manufac ture d by the We s t e rn El e c tr i c C om—
p any,and i s int ende d t o be us e d as a gene rat o r of
h i gh fre quency c urr ent s . The f i l ament o f th i s bul b
i s de s igne d t o op erate on ampere s when in nor-
mal Operat i on and w i th th i s current has a lif e o f
appr oximat e ly 1000 hour s . The f i l ament i s made o f
lime— c oated pl at inum and f or th i s rea s on re qui re s
suc h a smal l f i l ament current . The gr i d i s c ompo s e d
o f a numbe r o f turns o f tungs t en wire,s pac e d equal ly
on e i ther s i de o f th e f i l ament . Th e pl at e s are made
o f s he e t n i cke l about x I ! pl ac e d on e i ther s i de
o f the gr i d and i s pl ac ed far enough away t o wi th-
st and a vol t ag e o f 500 under normal Op erat i on . Wi th
th i s plate vo l t ag e and normal f i l ament c urrent the
output in the gr i d c i rcu i t i s about 1 00 mi l l i ampere s,
and in the pl at e c i rc ui t i s about 1 50 mi l l i amp ere s .
woul d not s t and vol t ag e s in the ne i ghbo rhoo d
o f t o vo l t s . The VTIand the
bul b s o f the General El e c tr i c C ompany were al s o
tr i e d,but woul d no t s t and vo l tage s a s h igh a s
the VT2 ,
s o no data w i l l be g iven on the s e ; but
the dat a t aken on the VT2wi l l b e f ound on the
f o l l owing page .
F igure 7 g ive s a s cheme o f c onne c t i ons
us e d by the General El e c tr i c C ompany in the c ours e
o f th e i r inve s t igat i ons . I t w i l l be s e en that
the generat or i s c onne c t e d t o a trans f ormer c on~
t aining two doubl e s e c ondar i e s,S and 82 . The s e1
might be c al l e d s ingl e s e c ondari e s wi th a l ead
brought out from the mi ddl e po int . Th e s e c ondary
SIi s d e s i gne d t o supply the f i l ament l i ght ing
current,wh i le the s e c ondary 8
2i s de s i gne d t o
supply the pl at e o f e ac h Keno tron w i th the h igh
vo l t age i t i s t o re c t i fy . The end s o f thrs s e c-
ondar y are c onne c t e d t o the pl at e o f e ac h Keno tron
and t he mi d dl e tap i s c onne c t e d in s er i e s wi th a
c ondens er o f s everal mi c r o farad s t o th e m i ddl e
top o f the l ight ing s e c ondary , The l o ad i s taken
o f f from e ac h s i d e o f th e c ondens er c,a s !
and Y ,as shown . The purpo se of thi s c ondens e r
in the re c t i f i e d al t ernat ing current .
A . C . t o D . C . Vo l t ag e f or 1 .
A . C . t o D . 0. Vo l t ag e f o r
ampere f i lament c urren t .
in t e s t ing the us e o f a VT!a s a Kenot ron .
RESEARCHES I N RADIO TELEPHONY
Part I I
Chapt e r I
C ons truc t i on and Us e o f the Dynatron .
The dynatron i s ano ther m emb er o f the
fami ly o f ho t c atho de dev i c e s,
wh i ch have be en
d eve l o ped at the Re s e arc h Lab orat o ry o f the
General El e c tr i c C omp any by Mr . A . W . Hul l, Ph.D .
In c ons truc t i on,th i s bulb re s embl e s th e
Keno tron and Pl i o tron,or or d inary th ree e l ement
vacuum valve,but in the pr inc ip l e s o f o pe rat i on
th e s e bulb s ar e ent ire ly di f ferent
1 . The Thre e El ement Vacuum valve ut i l i ze s
the pr inc i p l e o f c ont ro l l ing,by me ans o f th e gr i d
,
th e spac e c harge due to t he th erm i oni c c urrent
f l owing fr om the fil ament t o the pl at e .
2 . The Kenotron ut i l i ze s t he uni- di re c t i onal
prop erty o f the rmioni c current f l ow ing from th e
f i l ament t o the pl at e .
3 . Th e Dynatron ut i l i z e s th e s e c ondary
emi s s i on o f e l e c trons by a pl at e upon wh i c h the
pr imar y e l e c trons fal l . Th i s bul b,as i t s name
ind i c at e s,i s a gene rat or o f e l e c tr i c p ower
;
and f e e ds ene rgy int o any c i rcu i t t o wh ic h i t
i s c onne c t e d . I t i s l i ke a s e r i e s g enerat or,
in that i t s vo l tage i s pro port i onal t o the c ur-
rent thru i t,but i t i s ent i re ly fre e from th e
hys tere s i s and l ag that are inherent in Gene rat or s
and in al l devi c e s wh i c h dep end upon gas e ous i on—
ization.
The dynatron c ons i s t s o f a he at ing e le-
ment pla c ed ins i de o f an evac uat e d tube w i th a
p erf o rat e d pl at e c al l e d the ano de and a th i rd e l e-
ment c al l e d a p lat e . The ano d e i s p erf orate d s o
that,
a s th e f i l ament i s he at e d t o inc ande s c enc e
the ve l o c i ty o f the e le c tron s t re am i s not linder ed
on i t s way t o t he p l at e . Th e ve l o c i ty o f the s e
e le c trons i s qui t e h igh i f the pl ate p o t ent i al i s
h igh and on st r ik ing th e pl at e,c aus e s e c ondary
e le c trons t o be e j e c t e d from i t . The s e e l e c trons
are e j e c t ed w i th a ve l o c i ty suf f i c i ent t o c aus e
them t o s tr ik e the ano de,o r at l e a s t c ome in c l o s e
v i c ini ty t o the ano de,wh i c h i s be twe en th e pl at e
and the f i l ament,
and as the ano de i s ke pt at a
po s i t ive p o t ent i al the e l e c t rons are at trac t e d t o
and I the s ame current a s that through the bulb .
Then
C omb ining the two,
w e o b ta in
e1
92
I R!
but el
e2equal s th e t o t al vo l t ag e ac ro s s
c omb ination ,the re fo re we c an put ( e
1e
e qual t o E and then
B I ( r R!
And the vol t age ampl i f i c at i on e qual s
8
When the dynat ron i s c onne c te d in se ri e s w i th
a c i rcu i t c ontaining re s i stanc e,induc t anc e and
c ap ac i ty a s in F igure 1 5 we ge t a s the mathamatic al
s o lut i on
which r e duc e s t o 7
A th i s subj e c t i s
d the s c o pe o f th i s pap er ; but a s the
er w i l l f ind a very c ompl et e d i s cu s s i on
the Dynatron in the ! Pro c e e d ing s o f Rad i o
no more S pac e wil l b e t aken up he re .
a dynatron when the ext ernal res i s t anc e i s
HESEARCHES lN RAD I O TE LE PHONY
Part I I
C hap t er I I
The Us e o f a VTO
as a Dynatron
The VT2 ,
wh i ch has alre ady been de s c r i be d
in c hap t er I I o f Part I ; do e s no t work very sat i s —
f ac torily a s a dynatron . Th i s i s probably due
t o a re l at ive l arge spac ing be twe en the thre e
e l ement s c omp o s ing the tub e,and
,due t o a l e s s e r
ext ent t o the c o ars e gr i d that i s u se d in the
c ons truc t i on o f the VT2 ,
and b e c au s e o f th i s
c oars e gr i d b e ing use d,the de c re a se in surfac e
are a expo s e d t o the i oni c c urrent f l ow ing from
the p l at e t o t he gr i d when h igh po tent i al s are
us e d on the pl at e,i s no t a s great a s i f the gr i d
were o f f iner c ons truc t i on and,the ref o re
,th e
charac t e r i s t i c s o f the tube w oul d b e d i f f e r ent .
One int ere s t ing fac t that i s no t i c e d on the
grap h f o l l owing th i s page i s that i f do t t e d l ine s
ar e- dr awn thru th e po int s o f the same f i l ament
t emperature that thes e c urve s w i l l be as the do t t e d
c ur ve s sh own on the graph and s e em t o f o l l ow s ome
d e f ini t e l aw . Whe the r th i s,i s j us t due t o s ome
pe c ul i ar c ond i t i on o f the c i rcui t,o r
,i s one
o f the ch arac t er i s t i c prop e rt i e s o f the bul b
c an no t be de f ini t e ly s tat ed.
Th i s s e ems only t o b e true i f l ow vo l t age s
are us e d be c aus e read ing s takent at h ighe r vo l t age s
do no t c onf orm w i th tho se t aken at the l ower !
vo l t ag e s . Th i s might be due t o the fac t that a
c o at e d f i l ament i s u s ed and when h igh vol tage s
are u se d on the p lat e the charac t er i s t i c s o f the
bul b change s . In any c ase i t s ac t i on as a dyn
atron i s no t s at i s fac t ory .