A brief history of W2XF---subject to revision as I learn more

A Work In Progress

Additions, corrections and comments may be sent to frank at w2xf dot com
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The Empire State Building was completed in May 1931 and, at the time the tallest building ever built, towered 1,250 feet over New York City. The top of the building was designed to be a mooring for dirigibles, but that was soon abandoned as impractical because of excessively high wind currents. David Sarnoff, President of the Radio Corporation of America, had a vision that was to include the top of that building for a different purpose. He foresaw the future of television; and what better location for an antenna from which to broadcast television, than the top of the then tallest building in the world!

RCA leased the 85'th floor of the Empire State Building for a studio and transmitter location for experimental television broadcasts. RCA, through its broadcasting division NBC, applied to the Federal Radio Commission on July 1, 1931 for construction permits for the sight and sound channels of a television station, which were issued on July 24, 1931.
The call sign W2XF was issued in December 1931 for the "sight" channel of that station on an assigned frequency of 44Mc. The transmitter had an input power to the final stage of about 5Kw, giving an estimated power output to the antenna of about 2Kw. The sound channel of the TV station was separately licensed as W2XK for a 2.5Kw transmitter to operate on 61Mc. Both transmitters were located on the 85'th floor and used separate vertical dipole antennas extending from the top of the building. Previously the W2XF call sign, and it's predecessor 2XF, belonged to the Western Electric Company and Bell Laboratories, respectivly, which later became a part of the RCA group.

The 1932-1933 Television Tests

The experimental television broadcasts from W2XF during 1932 and 1933 used a mechanical Nipkow scanning disk to provide the video signal to the transmitter. (An electronic video camera, the Iconoscope, was under development at RCA's Camden, NJ facility but was not yet ready for field testing.) The early W2XF pictures were scanned by using the "flying spot" method of producing a picture signal. That method employed an arc lamp behind a spirally perforated disk to illuminate the subject in front of the disk with a bright spot of light. When the disk was rotated, the subject was progressively illuminated by a spot of bright light moving in a line across it through each successive perforation of the disk. Since each perforation in the spiral was a little lower on the disk than the preceding one, the subject was sequentially illuminated by spots of light
moving in a series of substantially horizontal scan lines from top to bottom. A photocell picked up the variations in light intensity reflected from the subject as each moving spot of light illuminated it, and sent a modulating signal to the transmitter corresponding with the variation in the light intensity during each scan line.

The video signals
received from the transmitter were reproduced by the newly developed cathode ray tube "kinescope," invented by Vladimir Zworykin in RCA's Camden laboratories. The variations in light intensity along each scan line reflected from the subject, were reproduced as a corresponding line on the face of the cathode ray tube. The image produced by the cathode ray tube could then be viewed in a mirror or enlarged by optically projecting it onto a viewing screen. W2XF began its testing in 1932 using a resolution of 120 lines per frame and 24 sequential frames per second.

In May 1932 RCA arranged a private demonstration of television progress from the W2XF transmitter for about one hundred executives and engineers of it's licensees. The 4 by 5 inch pictures, using live performers, were described by one of the guests as "fairly clear." Motion picture film reproduction was described as better, but not comparable with "home taking" pictures, which was the benchmark sought by TV engineers at the time.

RCA had an earlier experimental TV transmitter that was originally located at Van Cortlandt Park and later moved to the New Amsterdam theater on 42'd Street in 1930. That station
was originally licensed in April 1928 as W2XBS to broadcast on 2100-2200 Kc. The first tests using that transmitter were conducted using a Nipkow disk that provided a resolution of 60 lines per frame and 20 sequential frames per second. Many of these tests consisted of transmitting an image of a 13 inch paper mache statue of Felix the Cat on a rotating phonograph turntable, and were reproduced as a 2 inch picture at the receiver. Later, the resolution of the W2XBS signal was increased and eventually it was used for early tests the Iconoscope television camera tube.

It was apparent by the middle of 1933 that the resolution of Nipkow disks would not provide a satisfactory picture, and that flicker in the image at 20 or even 30 sequential frames per second was a serious problem. RCA sent its television development program back to the laboratory for further work. New technology to electronically scan the picture with higher resolution and a greater frame rate would be required to provide a picture that would be commercially practical.

The tests made from W2XF in 1932 and 1933 were of significance, however, because they were successful in proving that the use of  very high frequencies for television broadcasting was feasible in spite of their limited range. These tests were also the first major field tests to use the cathode ray Kinescope for viewing television images.

The Frequency Modulation Tests

Edwin Armstrong made at least four major inventions in the field of radio during his lifetime. His first major invention, regeneration, revolutionized radio transmitters and greatly increased the sensitivity of radio receivers. This invention was instantly embraced by the radio industry, as was his later invention of the superheterodyne radio. Armstrong sold both of these inventions to Westinghouse which became a part of the RCA group until its breakup on antitrust grounds. His invention of super regeneration, which was discovered by him almost by accident, greatly increased the sensitivity of regenerative radios. At the time of its invention, super regeneration was thought to be a significant advance in radio. RCA had rights under Armstrong's prior inventions through it's association with Westinghouse, and was determined to obtain the patent rights to super regeneration.

When RCA purchased Armstrong's super regeneration patent, he received a substantial sum of cash and sixty thousand shares of RCA stock, making him the largest individual stockholder in the company.  But super regeneration had serious technical problems and did not became commercially successful on other than a limited scale. One can wonder whether Sarnoff may have resented in later years the excessive price RCA paid to Armstrong for that invention. But RCA also received another important right as a part of that agreement, namely, the first right of refusal to acquire rights under any future inventions made by Armstrong.

Armstrong had worked for a number of years to develop a system of wide band Frequency Modulation. The work was conducted at the Marcellus Hartley Research Laboratories in the basement of Philosophy Hall at Columbia University, where he was a professor of electrical engineering. His wide band FM invention offered the promise of eliminating static, which was the major drawback of conventional AM radio at that time. By the end of 1933 his work had reached the point that he was ready to demonstrate his new "static eliminator" invention to David Sarnoff and other executives and engineers of RCA. These demonstrations took place in December 1933 and January 1934. The laboratory demonstrations were transmitted over only about fifty feet and were greeted with considerable skepticism about how well the system would work in actual field tests.

Since the previous mechanically scanned TV tests at the Empire State Building were ending, RCA offered to make the W2XF transmitter and antenna available to Armstrong for field tests of his FM invention. RCA obtained the license W2XDG from the Federal Radio Commission in May 1934 to enable Armstrong to use the W2XF transmitter for those FM tests.

Actually, Armstrong's wide band Frequency Modulation invention did not fit well into Sarnoff's vision of the future of broadcasting. Sarnoff had hoped that someone would invent a cheap little "black box" that could be attached to an existing radio to eliminate static. Armstrong's invention eliminated static, but involved a whole new system of radio. RCA had a huge investment in conventional AM radio, had three profitable national radio networks and was heavily invested in cranking out inexpensive radios for the general public. Commercializing FM would involve replacing conventional transmitters and radios with more expensive equipment in the middle of a depression, when discretionary money was scarce. But even more importantly, Sarnoff's vision was that television would be the next major advance in broadcasting. FM radio not only didn't fit into his plan, but could detract from it. It is perhaps ironic that commercial television broadcasting would employ FM as its audio transmission mode into the early part of the next century.

For the early tests, Armstrong set up a receiving facility about 70 miles from New York City, at the home of an old friend, George Burghard, at Westhampton Beach, Long Island. The first recorded reception at that location was on June 16, 1934. In Armstrong's words:

"The initial tests in the early part of June surpassed all expectations....The margin of superiority of the frequency modulation system over amplitude modulation at forty-one megacycles was so great that it was at once obvious that comparisons of the two were principally of academic interest."

"...perfectly quiet reception being secured through the heaviest thunderstorms when all the standard broadcast services had been rendered utterly useless."

But, it was felt that Westhampton was too favorable a location to give an accurate indication of typical reception conditions. Consequently,  the receiver was moved at the end of June 1934 to the home of Harry Sadenwater at Haddenfield, NJ, about eighty five miles from New York City. The results at the Haddenfield location were reported to be equally impressive. The W2XF transmitter, broadcasting FM with approximately two kilowatts, was reported to produce a signal at the Haddenfield location that was superior to the existing fifty kilowatt AM stations
under all conditions.

The Buzalski Paper

An interesting paper was published in Volume 1 of the Antique Wireless Association Review, written by Thomas Buzalski, Chief Transmitter Engineer, NBC, New York.  He writes that he worked along side of Armstrong to assist him during those early tests at the Empire State Building. Buzalski takes pains to specifically point out that it was the NBC technical staff's responsibility to make sure that the FM tests were made in accordance with the license granted for FM tests by the FRC.

Buzalski states that the record of visitors showed that Armstrong first visited the W2XF transmitter site on January 12, 1934, and again on January 19, 1934 "...to get information on W2XF for experimental work he is to do on it in the near future." Preliminary testing was conducted at Armstrong's request on the W2XF transmitter in February 1934 to test it's audio response and in March 1934 to check whether it's frequency bandwidth was sufficient for the FM tests. 
According to Buzalski, Armstrong moved his FM exciter equipment to the Empire State Building site in May 1934, the same month that RCA obtained the W2XDG license to enable him to use the W2XF transmitter for FM tests. However, according to another source, Armstrong actually moved his equipment to the Empire State Building in March 1934 which, if true, may shed additional light on the sequence of events that later transpired.

Buzalski states that the FM tests from W2XDG started on June 2, 1934 on 41 MHz, and on the evening of June 20, 1934 a special demonstration of organ music was transmitted for observation by the Chairman of the Board of RCA.

The Armstrong Paper

Armstrong described the FM tests from the Empire State Building transmitter in detail in a paper he delivered to the Institute of Radio Engineers in March of 1935. This was the first full public exposition of his FM invention after his original announcement in April of that year. He goes into much detail in his IRE paper about the frequencies used by his modulator to excite the transmitter.

The modulation equipment that Armstrong brought to the Empire State Building was designed to operate the W2XF transmitter on 44 megacycles, which was the frequency used for the television experiments. But the W2XDG license granted by the FRC for the FM tests, was restricted to testing on 40.6 and/or 41.0 Mc. Armstrong mentions in his paper that,

"Considerable trouble was caused during the early stages of the experiments by an order of the Federal Radio Commission requiring the changing of the frequency of the Empire State transmitter from forty-four to forty-one megacycles; thus necessitating the realignment of the large number of interstage transformers in the modulating equipment...and also retermination of the antenna."


Were all FM tests made in accordance with the FRC license?

Careful  reading of the two papers leaves a question whether some early FM tests may have been conducted from the W2XF transmitter before the modulator was modified to operate on 41 Mc.

The W2XF transmitter, according to Buzalski, had three doublers and one trippler which produced a 24X frequency multiplication of the input signal. Armstrong states in his IRE paper that,

“The frequency of the system was ordinarily controlled by a master oscillator operating at 1733 [sic] kilocycles which was multiplied by a series of doublers and triplers to forty four megacycles”


“The crystal control oscillator was replaced by the output of the modulation system shown in Fig. 20 in which an initial frequency of 57.33 kilocycles was multiplied by a series of doublers up to the input frequency of 1733 [sic] kilocycles.”

The transmitter input and modulator output frequency of 1733 Kc mentioned above, appears to be a mistake, and probably was 1833 Kc, which would have produced a transmitter output frequency of almost exactly 44 Mc (43.992 Mc) from the transmitter's 24X multiplication factor. (The W2XF transmitter would have produced a 41.6 Mc output if the input was 1733 kc.) At another point in the paper, Armstrong specifically states that his modulator had to have an output of 1708 Kc to produce a transmitter output of 41 Mc, which reflects that 24X multiplication factor.

Armstrong also states that his modulator used a fundamental frequency of 57.33kc, and had a series of doublers to multiply its fundamental frequency to provide its output frequency. The modulator would have to have had five doublers for a frequency multiplication of 32X to provide a suitable output frequency for the W2XF transmitter to operate on about 44 Mc from a 57.33 Kc input. Hence the modulator's  fundamental frequency of 57.33 kc would result in an input to the transmitter of a little less than 1835 Kc instead of 1733 Kc as stated in his paper, and would result in a transmitter frequency of 57.33 X32  X 24 or 44.029 megacycles. It seems likely that the modulator output was actually closer to 1833 Kc so as to produce an output of almost exactly 44 Mc.

It is somewhat strange that Armstrong describes these facts in his IRE paper, which he explains would result in a transmitter frequency of 44 Mc, if at least some FM tests weren't conducted on that frequency.  This leaves the possibility that Armstrong may have run some early tests using his original FM modulator to drive the W2XF transmitter on 44Mc, before the equipment was converted to broadcast on 41Mc in accordance with the W2XDG license, and perhaps even before that license was obtained.

It is also interesting that several American and European sources state that Armstrong began broadcasting FM signals using the call W2XF on 42.1 Mc, in May, 1934, and that the first comparison test with AM took place on June 9, 1934. Unfortunately,  they do not give the source for this assertion.

The Low Power Frequency Modulation Tests

Another interesting aspect of Armstrong's IRE paper is the mention that he had a 50 watt breadboard FM transmitter at the Empire State Building. That transmitter is shown at the Empire State Building site in Fig. 23 of his paper. The final stage of it is presently on display at the AWA Museum at Bloomfield, NY and
uses a pair of 852 tubes in the final stage of its amplifier. The description accompanying the transmitter at the Museum specifically describes it as producing 50 watts at 44 Mc. Armstrong describes in his IRE paper some FM tests that were made using 50 watts from the Empire State Building. He writes:

"It was noted by C. M. Burrill of the RCA manufacturing Company who made the observations at Arney's Mount that with fifty watts in the antenna frequency modulated (produced by pair of UX 852 tubes), a signal-to-noise ratio of the same value as the two-kilowatt amplitude modulation transmitter (eight kilowatt peaks) was obtained."


Armstrong states that these 50 watt FM tests were made with his breadboard 50 watt transmitter and it is apparent that he was comparing that transmitter, on FM, to the 2Kw W2XK transmitter on AM at that point in time.  The paper does not state whether those tests were conducted before or after the W2XDG license was granted for FM tests, and no mention is made of the frequency on which they were conducted. However, it is known that the Arney's Mount relay station was designed to receive and relay the 44 Mc television signals from W2XF to Camden, NJ.

The End Of The Frequency Modulation Tests

RCA requested Armstrong in April 1935, to remove his equipment from the Empire State Building so that the transmitters could be modified for new television tests that were to be undertaken later that year. Actually, the FM tests apparently continued into October while the W2XK sound transmitter was being rebuilt, but, by then the studio space being occupied by Armstrong was needed for construction work on the W2XF sight transmitter.

The 1936 Electronic Television Tests

On May 7, 1935 David Sarnoff made the startling announcement at RCA's Annual Stockholders Meeting that the company would begin a one million dollar test program to bring television out of the laboratory and into the field. He further told his stockholders that regular television broadcasting would start by June of the following year. However, he was quick to point out,

"... while television promises to supplement the present service of broadcasting by adding sight to sound, it will not supplant or diminish the importance and usefulness of sound broadcasting."

RCA was much concerned that premature rumors of television being available soon, would diminish sales of conventional radios. This announcement was also incorrectly heralded as lifting the heavy secrecy that had surrounded RCA's television developments up to that time.

was actively testing at it's research facility in Camden, NJ, a new TV technology, making use of the electronic "Iconoscope" camera tube, developed by Vladimir Zworykin, to replace the scanning disk. The Iconoscope used a tube, similar to a cathode ray tube, having a matrix of photoelectric spots on which an image was focused. The charged spots were then scanned with a beam of electrons, moving in lines, to produce a current corresponding with the image. The current was amplified and used to modulate the transmitter. The signal from the transmitter was reconstructed as a image by a cathode ray tube "kinescope" at the receiver.

A great advantage of the Iconoscope was that the number of scanning lines, and hence the resolution, could be increased significantly over the practical limitations of the Nipkow scanning disk. In addition, the camera-like Iconoscope allowed much greater flexibility of lighting and subject matter, especially for outdoor scenes.

By 1934 the Iconoscope experiments at Camden employed a resolution of 343 lines, which produced a much superior picture. Just as importantly, they used a frame rate of thirty
frames per second with a field frequency of 60 frames per second, interlaced, which fully overcame the flicker problem.  These tests involved transmitting from the Camden research labs with nominal power on 49 and 50 Mc. Similar tests were also being conducted at this time from RCA's W2BXS transmitter at the New Amsterdam Theater. By the middle of 1935, Zworykin's Iconoscope camera was ready for full scale field testing from the Empire State Building.

To accommodate the new tests, the W2XF video transmitter was rebuilt as a 10 Kw transmitter, having an output of about 7.5 Kw, designed to transmit on 49.75 Mic, and the W2XK sound transmitter was rebuilt to operate on 52 Mc. W2XF was now able to provide an all-electronic video signal from an Iconoscope source having 343 lines and 30 interlaced frames per second. The Iconoscope cameras were located in the RCA studios at Radio City and linked to the Empire State Building transmitter by both an underground coaxial cable and a microwave link.

Page 63 of the Second Annual Report of the Federal Communications Commission to Congress for the fiscal year 1936  describes this event as follows:

"On June 29 television broadcast station W2XF began operating in the Empire State Building, New York, on an experimental basis for public reception. A few receivers were distributed to selected observers. It was reported that the operation would continue as the  experimental work permitted."

Actually, only about 90 television receivers became available and all were in the hands of RCA executives and engineers. None were available to the public. Strict secrecy still surrounded the results of the transmissions. The New York Times headlined the event with:

"Test Of Television Started In Secret"

 "...observations on the quality of the images will be kept secret. The only indication that the tests reveal signs of success is found in the fact that licensees of the Radio Corporation of America will be invited to see the 'show' and apparatus on July 7."

In fact, the engineers had encountered serious noise problems in the amplifiers, and it was not until the early morning hours of July 7 that the pictures were reported as being worth showing. These first, green phospor images were reproduced by 9 inch round tubes having 5X7 inch masks, which were deemed by most viewers to be too small for wide acceptance. The receivers had a total of 33 tubes and 14 control knobs at that time.

However, the June 29 event represented a major milestone in the development of television in the United States. An all-electronic, a 343 line "high resolution" television signal was now being broadcast to home viewers throughout the New York City area, by W2XF, on a somewhat regular basis.
These broadcasts were the first major field tests to use the Iconoscope camera and, arguably, may have been the first regular broadcasts of all-electronic television in the United States. In a statement to the Press on November 6, 1936, David Sarnoff said:

"That date [June, 29, 1936] marked the beginning in this country of organized television experiments between a regular transmitting station and a number of homes."

A few months later, on November 6, 1936 a major demonstration from W2XF was held for the press before about 250 invited guests assembled in Radio City. It was the first time that RCA had demonstrated a practical working television station to the Press under actual field conditions. This event also introduced receivers having a much improved 12 inch kinescope tube that provided 71/2 x 10 inch pictures. Fifteen of these new receivers were set up at Radio City for the demonstration. The program included talks by the President of NBC and David Sarnoff, President of RCA, on the progress and challenges of television development, as well as entertainment features.

The New York Times reported on January 3, 1937 that the Empire State Building transmitter would be shut down early that year for conversion to 441 line pictures. The Third Annual Report of the FCC to Congress for the fiscal year 1937 states:

"One television station in New York City broadcast for public reception using a high picture definition of 343 lines, until December 1936 when operations were discontinued in order to alter the equipment to transmit definition of 441 lines. Demonstrations of this definition in April 1937 were successful, and the improvement in the picture detail was very noticeable."

It is highly probable that this FCC statement refers to the Empire State Building operation. It is also likely that the W2XBS call was transferred to that operation at about this time. The 441 line standard had been recommended by the Radio Manufactures Association for TV broadcasting. Later the NTSC group was formed and recommended the finally adopted 525 line standard. It is not clear whether those first 441 line pictures from the Empire State Building were broadcast as W2XF or W2XBS.

Confusing History

Researching the history of W2XF has led to a number of omissions and contradictions in the literature.  Some references state that the 1933 television tests from the Empire State Building were made from RCA's earlier experimental station, W2XBS. However, Thomas BuzalskI, who was NBC's chief transmitter engineer at the Empire State Building, clearly states in his AWA paper that those 120 line tests were broadcast from W2XF. Similarly, many references state that the all-electronic television broadcasts that were begun on June 29, 1936 were made from W2XBS. However, the 1936 FCC Report to Congress clearly states that these broadcasts emanated from W2XF, as does an article in the August, 1936 issue of Radio Craft Magazine.

Part of the problem may stem from the heavy secrecy that surrounded the TV experiments from W2XF. Confusion may also have come about because some of the programming being broadcast by W2XF originated from television studios in Radio City which were associated with W2XBS. By 1936, these studios were connected to the Empire State Building site by both a coaxial cable and a microwave link. In addition, it may have served the cause of historical simplicity to trace RCA's television history directly back to its original 1928 TV station, which eventually took over the Empire State Building location. The history on the Internet of its successor, WNBC, does not specifically mention the involvement of  W2XF at the Empire State Building, and if not read carefully, could be misunderstood to imply that the 1931 and 1936 television broadcasts from the Empire State Building were made from W2XBS.

Other articles state that Edwin Armstrong broadcast FM transmissions on 42.1Mc using the call W2XF,
but there does not seem to be any clear evidence of that. It is clear that W2XDG would have been the proper call sign under which the broadcasts should have been made after that license was granted.


Eventually, the W2XBS call sign was transferred to the Empire State Building TV operation. The call W2XF seems to have disappeared sometime after February 1937, when it still appears in a New York Times listing of one of the twenty currently licensed experimental TV stations. W2XBS became NBC's premier television station and was introduced to the public at the 1939 World's Fair with the famous broadcast of the opening remarks by FDR on April 30 of that year. On the same day RCA  model TRK-12 television sets first became available to the public in New York City stores for $600.

  W2XBS eventually received a commercial television license with the call WNBT, and became one of the first two television stations in the United States to began commercial operation on July 1, 1941. Through a succession of call sign changes, WNBT
became the present WNBC in 1992. It also appears that RCA may have continued to operate a low power station with the call W2XDG (the license obtained for the Armstrong tests)  as an experimental, high frequency, AM station from November 1935 to early 1940 according to one source.

Finally, in June 2007 the Call W2XF was assigned by the FCC to me. I feel extremely fortunate to have received a call with such a rich and distinguished history in the fields of both  television and FM broadcasting.

Frank Decker