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.
DR. C.FRAiTCIS JSHKIffS
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.
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.
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.
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).
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.
Frames taken from early (1928) Radiomovies broadcasts
from W3XK. The Jenkins Laboratories, Washington, D. C.
Frames taken from early (1928) Radiomovies broadcasts
from W3XK. The Jenkins Laboratories, Washington, D. C.
Frames taken from early (1928) Radiomovies broadcasts
from W3XK. The Jenkins Laboratories, Washington, D. C.
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.
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",
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.
The kilocycle channel
now broadcast from the
at Wheat on is no./ 2350
to 2950 for
and 20 CO
to 2100 for local receivers. With
broader frequency banc-
, clearer pi
ctures are t
were formerly possible
GROUND PLAN OF THE STATION AT WHEATON.ID.
\4nip//f/ct" 41*1/ ' /Ybie(//A; fc-'t- j
Skefch &#/■ /a ^cg/e
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.
The Jenkins Lens-disc Radiomovies transmitter of 1928.
Lenses arranged in a circle; film moves continuously.
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
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,
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
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
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
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-
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
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.
SIHG-LE TARGET CATHODE- GLOW HE01J TUBE
SII.'ILAB TO ONE USED IB" THE JENKINS RADIOVISOR
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
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
The mechanism of the Jenkins Radiovisor. Motor rotates the drum for
scanning the picture.
Four-cathode lamp used in the Drum-scanner of the Jenkins
Radiovisor (2-inch square picture, unma<niitied).
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
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
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.
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-
BALTIMORE AND OHIO RAILROAD COMPANY
Admission to the
Phi Mu Honorary Engineering Fraternity
University of Maryland,