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Full text of "The construction and operation of the Jenkins Television Laboratory at Wheaton, Maryland : a thesis / prepared by pledge Herbert William Cooper"



TEE COHSraUCTIOB AID OPERATIOfl OP THE JBNKIIS 
TELE7I3I02 WBOEAIOBI AT 1HE1T0E,MD. 



A thesis prepared by Pledge 
Herbert William Cooper 
as a part of his initiation requirements for membership 
in Tau 3eta ?i, Maryland Beta Chapter, the honorary 
engineering fraternity at the university of Ilaryland. 



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DR. C.FRAiTCIS JSHKIffS 



SUMMARY 

The history of the Jenkins Television laboratories 
at Wheat on .I'd, "began on the evening of July 2 ,1928. On this 
date, Dr. Jenkins began his first of a series of regular 
broadcasts of television signals, from his experimental 
laboratory at 1 J? 1 r J Conn. Avenue , K . AT. , V -'.shine ton, D. C . Encouraged 
by his early success, Dr. Jenkins continued to bro- dcast, until 
he was forced to search for a location further away from the 
residential section, in which he was situated, because of the 
interference caused by his experimenting. 

At this point, the location of the present station 
at .Vheaton was determined, and construction began in February, 
1929, With the conscientious aid of his fine staff, Dr. JenkiHS 

a"!ile to broadcast the initial program from this newer and 
more powerful station in April, 192>>, Silhouettes formed the 
first program features, but developments took place rapidly, 
so that the first half-tones were sent over the air in 
November, 19.30 , 

Broadcasts are now done entirely from the face of 
film, on a regular schedule, but soon pictures taken from liv- 
ing figures will be transmitted. Since the time of the trans- 
mission of the first half-tones, progress at the station has 
been very rapid. Even at the present writing, the power of the 
station is undergoing the process of change. Consequently, 
any apparatus discussed in this report, or even the present 
theory of television is liable to be rendered obsolete nd 
discarded in a very short time. 



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HISTORY AND BACKGROUND OF THE LABORATORY 

The story of the construction of the Jenkins labor- 
atory at Wheat on ,Kd. , is a short one. It is necessary to del«e 
farther into the history of television to learn the purpose 
for which it was erected. 

One who might be called the father of television in 
the United States is Br. C.Francis Jenkins, born of Quaker par- 
ents at Dayton, Ohio in 1868. He is the outstanding pioneer in 
this new industry, and has probably done more in practical 
experimental work: than any other man in America. 

His discoveries and inventions relating to televis- 
ion were made in 1923 and 1924. Previous to this time, he had 
been working with the problems of the transmission and accur- 
acy in reception of radio pictures of still objects. This art 
he brought to a high degree of perfection through the use of 
his invention of the prismatic ring for scanning the pistures 
or objects transmitted. Television, however, brought newer and 
more difficult problems. 

Dr. Jenkins was fully aware of the value of the 
American amateur in developing the perfection of radio trans- 
mission, especially in the short wave range to which televis- 
ion signals arc restricted. It was with the idea of obtaining 
the valuable assistance of the amateur that the Jenkins lab- 
oratories began the first broadcast as a licensed station on 
July?, 1928. This date inaugurated the beginning of the trans- 
mission of television signals on a regular schedule. 



-2- 

The initial Tjroad.oB.sts were especially for the 
Tjenefit of the members of the Amateur Radio Relay League of 
which the Jenkins Laboratories are members • This first broad- 
oast was through the station VT5XK, located at 1519 Connect- 
icut Ave. ,N.W. , Washington, D. C. on a frequency of 6420 kilo- 
cycles, for distant receivers ,with a wave length of 4-7 meters, 
and 1605 kilocycles with a wave length of 186 meters for the 
benefit of Washington listeners and amateurs of the surround- 
ing territory. The power of this station was ^ watts. 




THE FIRST HOME OF STATION W^XK ON THE 
SECOND FLOOR OF THE MARKON BUILDING AT 1519 CONN. AVE. 



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Distinguished visitors on the occasion of the inauguration by the Jenkins Laboratories of the first regular scheduled broad- 
casts of Radiomovies July 2, 1928. Left to right: Capt. S. C. Hooper, Navy; C, Francis Jenkins ; Gen. George 0. Squire; 
Capt. Guy Hill, Signal Corps, Army; Commissioner Harold A. LaFont; Commissioner Judge Ira E. Robinson; Commissioner 
Sam Pickard; and Carl Butman, Secretary Radio Commission (in rear). 



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Their first broadcasts consisted only of silhouette 
movies in the black and white and transmitted from yhe face of 
a film. The program lasted for an hour on the evenings of 
I londay, Wednesday and Friday, The reason for broadcasting silhou- 
ettes was that such pictures were simpler, covered a narrower 
frequency band, and were therefore simpler for the amateur to 
pickup and adjust his receiver to. Short subjects were first 
used, and more elaborate stories were gradually worked into the 
program which was ^transmitted! Reports were immediatel. forth- 
coming from the listening amateurs, showing the interest of the 
American radio fan in the new invention. 

With the shower of reports from the amateurs also 
came letters of complaints, The Jenkins Laboratories at 1^1° 
Conn, Ave. are in the very center of the city of v/ashington, 
consequently , a great deal of interference was caused by the 
operation of the station at this point. Dr. Jenkins was there- 
fore forced to look elsewhere for a position to place his stat- 
ion such that no interference might be caused. 



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Frames taken from early (1928) Radiomovies broadcasts 
from W3XK. The Jenkins Laboratories, Washington, D. C. 



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Frames taken from early (1928) Radiomovies broadcasts 
from W3XK. The Jenkins Laboratories, Washington, D. C. 



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Frames taken from early (1928) Radiomovies broadcasts 
from W3XK. The Jenkins Laboratories, Washington, D. C. 



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CONSTRUCTIOH OF THE STATION AT WHEATON,MD. 



A place which, filled Dr. Jenkins requirements was 
located on the estate of one of his friends, at Wheaton,rd. 
This position was very desirable from the point of causing 
interference, as comparatively few residences were near it. 
Arrangements were completed and construction operations begun 
at this point in February, 1 929. 

The panels for the transmitter units were built by 
Masseurs Knight and Link of Passaic, New Jersey. Instalments 
for the station were built and put into operation by members 
of the Jenkins Laboratory Staff. According to Dr. Jenkins, 
the members of his staff who erected the station deserve 
particular praise for their inventive genious shown in the 
skillfull manner in which they designed and erected the app„ 
aratus of the station which was of a higher power and diff- 
erent frequency than the one at Conn. Ave. The first broadcast 
from this station took place in April, 1929. 
STATION '.VJXK AT WHEAT ON .LCD. 




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The station is now situated in a small, five-room 
bungalow which is shown. Overhead are the two, large steel 
skeleton towers, one hundred twenty-five feet tall. In this 
one house are situated two transmitters, one known as VY3XK 
and the other as W3XJ. Both operate on short wavelength. 
Station W3XK is used mainly for the transmission of the tele- 
vision pictures on a wave length of 146 meters, while station 
W3XJ is used primarily for the transmission of voice on a 
ave lengthof 1 36 meters . 

Pictures are broadcast from these stations directly 
from film in a manner somewhat similar to .h< broadcast from 
the Conn. Ave. laboratories. Each set of pictures are preceded 
by an announcement of the film about to be presented, by he 
station V/3XK- The film is then transmitted over station W3XK 
and the voice station, W3XJ, describes the events depicted by 
the pictures. The film is completed by the word "END", 
prominently displayed. 

To transmit from these two si at ions, two antennas 
are required. The antenna used by 'he picture station,W3XK, is 
strung between the two radio masts, and has a length of 2 
feet The antenna for the voice station, W^XJ, is s4ung on a 
slant, running from the top of one of the masts to the ground. 

With the erection of this higher powered station 
the frequencies were also changed. Through the courtesy of the 
Federal Radio Commission, television stations all over the 
country were granted a frequency band of width of TOO kilo- 
cycles. This greatly increased the range of frequencies 
obtainable in broadc. ,st , in contrast to the ten kilocycles 
band which was formerly available. 





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The kilocycle channel 


now broadcast from the 


Jenkins 


stations 


at Wheat on is no./ 2350 


to 2950 for 


distant lis 


teners , 


and 20 CO 


to 2100 for local receivers. With 


this increas 


e of 


power and 


broader frequency banc- 


, clearer pi 


ctures are t 


road- 


cast than 


were formerly possible 


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GROUND PLAN OF THE STATION AT WHEATON.ID. 



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The layout of the station is shown in a diagram- 
matic sketch. In the central portion of the southern part of 
the house is a room about five fee' wide and aboiit ten feet 
long. This room contains the first elements of the television 
system. Here is the analyzer and the two amplifier and modulat- 
or units. The next room on the right is the transmitter room, 
containing the transmitter units and the microphone for the an- 
nouncements. On the northeast corner of the house is a room 
which seems to be arranged as a kitchen. Diagonally opposite 
is the receivin . room, containing two receiving sets by which 
the transmitted signals are closely observed and checked for 
clarity, flicker and other details. Directly north of this 
room is situated the small, but comfortable living room, tastely 
decorated, furnished with several chairs and another r dio 
of a commercial model. On the table in the center of the room 
is he list where visitors to this station are requested to 
register their identity. This list holds the names of many 
important and famous people. Visitors are always welcome and 
are very cordially received. 

To return to the broadcasting equipment, consider 
first the analyzer, as this is the beginning of the transmis- 
sion of pictures. An idea of the appearanceof this machine 
may be obtained from the picture inclosed, showing Dr. 
Jenkins standing by the apparatus formerly used to transmit 
pictures from the Conn. Ave Station. (Note: It was not per- 
missible to take pictures of the broadcasting equipment, so 
the machinery is being described from photographs of equip- 
ment now obsolete, corrections being noted inthe description. 



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The Jenkins Lens-disc Radiomovies transmitter of 1928. 
Lenses arranged in a circle; film moves continuously. 



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This piece of apparatus is so arranged that the 
film to be analyzed is supported on a framework and moves 
ver ically between the sides of a small sleeve, in amrnner 
similar to the construction of a motion picture projector. 
The film to be shown is of the standard motion picture size 
with the usual holes placed along the side. Into these holes 
fit knoblike projections, arranged circumferentially on a 
small cylinrical drum, about one inch in diameter. This drum 
draws the film from the lower reel to the upper. The shaft by 
which this drum is driven is geared to a second shaft which 
in turn is driven, by a second set of gears ,by a small, 60 
cycle synchronous mot or t which is running at 180C R.P.H, 
On th same shaft to which the drum is geared, is directly 
attached a thin, metal disc, about eighteen inches in diameter. 
This corresponds to the disc appealing in the photograph of 
the analyzer. In the photograph, the disc is shown -tudded with 
forty-eight tiny lenses, but inthe present apparatus, which 
is considerably more recent than the one shown, the lenses 
are replaced by narrow slits, about one-sixteenth inch in 
width and one-half inch long. 

The gears mentioned are so arranged that as the 
motor rotates at 18OC R.F.I.'. , the film moves at a rate of 900 
pictures per minute, and the disc rotates at a speed of 900 
R.P.r. Therefore, for every picture frame, ther is a correspond 
ing complete revolution of the disc t This disc is placed in 
lehind of the moving film. In front of the film is a very 
strong source of light which is focused on a narrow horizontal 



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Bllt in the metal sleeve through, which the film moves, The 
focusing power consists of three lenses, namely: a plano-convex, 
double-convex and a plano-convex. 

The width of the slot thro hioh the light passes 
is approximately equal to one forty-eighth of the length of 
the picture. Immediately behind the film is a secondE set of two 
piano convex lens which focus the light coming through the film 
on to the revolving disc. After passing through the slots of 
th/ disc,th light again is focused through a series of two 
plano-convex lens es. From these, the pinpoint of light impinges 
on a photo-electic cell. 

PRINCIPLE OF THE ANALYZER 

To understand the principle involved.it would to 
start again at the beginning of the analyzer apparatus. Power- 
ful, focused light is allowed to fall on a narrow slit, past 
which the film moves, which is about to be analyzed. It then 
falls on the rapidly moving disc. Now this disc is moving at 
such a rate that it revolves once for every picture frame 
passing by the horizontal slit. The result , then, is the same 
as would be obtained by keeping the film stationary and draw- 
ing 48 horizontal lines of light across the film, each below 
the preceding one, and each composed of tiny pinpoints of light 
for as each slit moves across the horizontal line formed by the 
horizontal slit, it allows only a small portion, the width of 
the slit in the disc, to pass through. Hence, as the disc rotates, 
each slit allows a series of pinpoints (or a line ) of light 
to pass throughi a one slit passes b . - edge of the film, 



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a second begins at the opposite edge of the film, only slight- 
ly lower. At any given instant, only a pinpoint of light is 
passing through the disc and is determined by the slit in fromt 
of the film and the slit in the disc, thus: 

It is evident why this machine is termed an analyser 
for it actually breaks up the pisture into its component val- 
ues of light and darkness, just as a half-tone picture produced 
by the screen method, for use in newspapers and magazines, is 
broken up injo dots of varying intensities of light. 

The light from the analyzed picture now strikes on 
the photo-electric cell. This is, in reality, a form of generator, 
It consists of a glass bulb with the rear wall coated with a 
layer of silver. Over this coating is placed a layer of potass- 
ium. One electrode is formed by the potassium and a second by 
a loop of wire projecting from the cell. The bulb is filled 
with hydrogen. As light strikes the potassium, it emit? elect- 
-rons. This tiny electric current is directly proportional to 
the amount of light on the cell. It is obvious, the, that the 
value of the current from the cell corresponds ,at any instant 
to a light intensity at a point in the analyzed picture. 

This minute current , which is of audible frequency, 
is very much to small for broadcact purposes, and must be amp- 
lified greatly. This is accomplished by passing the current 



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through four stages of amplification followed by four more 
stages of power amplifier. The frequency of the impulses 
from the cell are modulated to radio frequencies in a two 
stage modulator. 

The next stage of the system is the transmitter. This 
is entirely too complicated to discuss adequately in the 
space here alotted, but it might be said that the frequencies 
are controlled by a quartz crystal as in voice broadcasts, The 
system is completed by sending out the impulses over the 
radiating antennae. 

The chief difficulty encountered in television 
transmission seems to be that the frequencies from pictures 
run into about thirty and forty thousand cycles per second, 
about three times that of voice broadcasts. 
THE RECEIVER SYSTEM AT STATION '.'OXEC 

Another important unit in the system of the Jenkins 
station is the receiving set which is used to check up on the 
quality of the pictures broadcast td. Ihis consists of a set 
which is sold commercially by the Jenkins Corporation, and 
which is known as a "Radiovisor". It is composed of two short 
wave receivers , one to be used for voice and the other, for 
the television signals, so that both may be received simult- 
-aneously. 

The set for receiving the television pictures con- 
sists of a short wave set coupled with a drum scanner. The 
scanner is the heart of he machine, for it is this piece of 
apparatus which changes the electrical impulses from the 
transmitting station into light impulses, and assembleses 



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them in the proper sequence ' o form a picture. 
THE JE1IKINS RADIO VISOR 




The drum scanner consists of a hollov/ metal cyl- 
-inder, about seven inches in diameter, three inches Ions » 
with a one -sixteenth inch wall. There is a hub on the outside 
of the drum which slips on the ,V n shaft of a small synchron- 
ous motor. On the peripheral wall of the cylinder are 48 tiny 
holes about 1/32" in diameter. These holes are arranged on 
four helical turns, the turns being „" apart and the holes 
spaced 2" apart circumferentially. Inside the drum is a single 
target cathode-glow neon tube, held stationary by a support 
above the drum. 



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SIHG-LE TARGET CATHODE- GLOW HE01J TUBE 
SII.'ILAB TO ONE USED IB" THE JENKINS RADIOVISOR 



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In front of the drum and geared to the motor which 
drives the drum, is a flat metal disc with spiral slits cut 
in it. These slits ars so arranged that as the drum rotates, 
only one of the 48 holes on the drum shows at a time, and that 
only as long as it passes across the face of the neon tube 
target. The result is , that ! he top hole of the drum passes 



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across the face of the target and disappears ;next,thR hole 
"below the first one repeats the procedure .until finally the 
whole target is cover d with imaginary lines traced by the 
holes in the drum. It id evident that this is just the reverse 
proces- of analyzing. The neon tube target is so hooked up 
as to glow with different intensities of light corresponding 
to the impulses from the transmitting station . The glow from 
the tube is then made into a "beam of light by the hole in the 
drum scanner, and this beam traverses back and forth across 
the face of the target until the impulses are all arranged in 
their proper order, so that the picture finally appears as 
transmitted, The color of the picture is pink and black. 

Formerly, the neon tube had four targets for produc- 
ing a 2" picture, such as is made by the single target tube of 
today .These targets each lighten 7 a separate helical turn and 
the disc in front of the scanner was not necessary .Ifcere vaa 
a hollow drum inside the scanner and holes corresponding to the 
holes on the outside wall, These two sets of holes were connect- 
ed together by hollow quartz rods to make a more efficient 
transmission of light to the exterior of the drum, but this has 
proven impractical in commercial use, so that it was done away 
with and the single tube subs tut ed together with the elimin- 
-ation of the quartz rods. 



EARLY TYPE OF SCALER USED IN THE JENXDTS 
RADIOVISOR 



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The mechanism of the Jenkins Radiovisor. Motor rotates the drum for 

scanning the picture. 



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Four-cathode lamp used in the Drum-scanner of the Jenkins 
Radiovisor (2-inch square picture, unma<niitied). 



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Ak there are four helical turns on the drum, it takes 
four turns to make a complete picture . The speed of the drum 
must therefore be four times the speed in R.P.I.'., of the analy- 
zer speed in pictures per minute or 36OO R.P,M# In front of the 
scanner is a large plano-convex lense which magnifies the 
picture until it is about six inches square, so that five peopie 
can watch it comfortably. Because the synchronous motor runs 
from the same supply a< the transmitter and analyzer, the pict- 
ures are always stationary. The speed of the pictures received 
and those transmitted must always be in exact synchronism, 
There is a switch on the machine, however, for bringing the 
pictures into frame to compensate for a slight tendency of the 
motor to "hunt 11 . 

This receiver gets its impulses by wire. There is 
however, a receiver, talcing its signals from the ether which 
is used to check up on the voice quality from the transmitter, 

The two yo\ing expert members of Dr. Jenkins staff 
who Assisted in assembling the apparatus of this station when 
it was first constructed., also now maintain it. They are 
Mr . Theodore Delete and Mr Paul Thomsen, 

Until just recently, the accepted American Television 
method of scanning was from left to right and top to bottom, it 
a speed of fifteen pictures per second and 48 lines per picture. 
The Jenkins station conformed to this standard, but it is being 
changed to meet the newer standard of ictures per second 
and sixty lines per picture. It is expected that this will 
produce pictures of much greater clarity than before obtain- 
able. The power of this station is also being increased. Because 



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this is a transitory type of station, being in the amateur 
stage, no apparatus blueprints were available. 

The station now broadcasts from 7P»M. to8 P.M. 
Eastern Standard Time every evening except Sunday, using 
both transmitters. From 8 p,r, to 9 P.- 7 '. .station W}JK carries 
on the broadcasts, W3XJ being required by law to sign off 
in order to allow a station in New York to transmit without 
interference. 

The world is about to witness the birth of a new 
art , television. Very soon in the near ruture, it will hail 
this art ] ighest aeheivei -: fa of the inventive genius 
of men, all over the face of the globe, who are striving to 
make the world a better more interesting place in which to 
live. One of these men is Dr. Jenkins t and his laboratory 
at Wheaton,M4. f is an important .integral part in the develop- 
ment of this great invention to the high degree of perfection 
which it truly deserves. 



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BIBLIOGi^PiA* 



Vision by iiadio.nadio Phot ©t raphe and Photofcrams 
published by the Jenkins Laboratories, inc.,19£5. 



hadio Liovies, hadio Vision, Television 
published by the Jenkins Laboratories, Inc. 15£9 



Television: The World's First Television 
Journal, published in England. ^ow cliscontiued. 



iraotioally all of the material usea in 
this thesis was obtained from personal interviews with 
Dr. Jenkins, Mr.btuart Jeniis.one of ur. Jenkins staff 
members; *.ir. raul Ehomsen and Sir. 'I'heodore i»elote at 
the Wheat on station. 

j-iie writer is deeply indebted to them for 
the help whioh they have so generously profered and 
wishes to here express his gratitude tor their essi st- 
ance. 



EARLY HISTORY 

of the 

BALTIMORE AND OHIO RAILROAD COMPANY 

by 

ULPIANO CORONEL 



Paper Presented 
for 
Admission to the 
Phi Mu Honorary Engineering Fraternity 
University of Maryland, 



May 1924.