On Dec. 24, 1906, Reginald Fessenden transmitted an audio broadcast of spoken voice and music to a few listeners. It was a broadcast in that it was not meant as a point-to-point message. Since then, radio has grown in its scope and coverage, and the technology used to create it has provided the tools to improve it and allow it to extend beyond the traditional airwaves.
Last month, we profiled the event and the innovator. This month, we detail the top 100 technical innovations that have influenced radio, as nominated by you, the reader, and organized by a panel of radio broadcast engineers. The entries for 100 through 21 are listed alphabetically. The top 20 are ranked in order. You may feel that we left something out or that something is not being given the ranking that it deserves. If so, tell us about it at firstname.lastname@example.org.
— Chriss Scherer, editor
Technology descriptions by Doug Irwin
100 to 21*
* These are in alphabetical order.
|45 rpm record
||AM directional antennas
|AM top loading
|Audio over IP
||Audio Precision System One
|Broadcast Electronics FM30 folded-wave RF amplifier
|Circular polarized FM antenna
||Coherer radio detection circuit
||Comrex frequency extender
||Dielectric switchless FM combiner
||Dolby noise reduction
|Dorrough Loudness Meter
||Editall splicing block
||Emile Berliner flat-disk recorder
||Electric transistor console
|Gramaphone disk recorder
||Hallikainan and Friends TEL-171
||Kahn Communications AM stereo
|Mid-level (split-level) combining for HD Radio
||Modulation Sciences CP-803
||Modulation Sciences Sidekick
||Moving-coil dynamic speaker
||Optical recording (CD-R)
||Orban Optimod 8000
|Orban Optimod-FM 8200
||Paper recording tape
||Potomac AG-51, AA-51
|Prime Image Cash and 25-Seven ATM
||QEI solid-state FM
||RCA BTA 1R
||Reel-to-reel tape technology
||Solid-state memory cards
|Stereo patent (Blumlein)
||TDM audio routers
||Wire recorder (telegraphone)
20. Cylinder recorder
While working on a device that would send telegraph messages in an automated fashion, Thomas Edison stumbled on the idea of recording and playing back the human voice. Thus was born the cylinder recorder; the predecessor to all other recording devices and the germ of the technology used by the music business. The device was a hand-cranked cylinder that was covered with tin foil; one diaphragm attached to a stylus was used to etch the track into the foil and another lighter stylus was used during the playback. For the first crude versions, the tin foil itself would only last for a few plays and couldn't be removed from the cylinder. Later the cylinders were made from wax and could be played multiple times. From the turn of the century to the early 1920s, cylinder recordings were quite popular, only to be surpassed later by 78 rpm records. Edison stopped making the cylinders in 1929.
19. Zenith-GE FM stereo
In 1961, the FCC selected the Zenith-GE system as the method that would be used to transmit stereo signals on the FM band. One of the more important considerations during this transition was backward compatibility—making sure that older FM mono receivers would still be usable. For this reason, FM stereo uses a matrix system. Left and right channels are added together and make up the mono signal (L+R); at the same time, right is subtracted from left, thus forming a L-R signal. When the L+R and L-R are added and subtracted, discrete left and right are recreated.
For transmission, the L-R signal is mixed with a 38kHz signal to form a double-sideband, suppressed carrier signal that is added to the baseband and occupies the spectrum from 23kHz to 53kHz. A 19kHz pilot tone is also transmitted for synchronization of the stereo decoder on the receive side.
The development of stereo transmission on FM followed the widespread introduction of stereo LPs in 1958, and played a significant role in the popularization of the FM band. Many early FM stations broadcasted classical music, taking advantage of the newly developed technology in attracting listeners.
18. Perceptual audio coding
Perceptual audio coding takes advantage of the way human hearing works in the time and frequency domain by not encoding sounds that are ultimately imperceptible, and by efficiently using the minimum number of bits to encode the sounds that are perceptible. The ultimate goal is to fit as many useful bits as possible through what is typically a data-bandwidth limited path between the program source and the far end: the listeners. Lossy Codec is the name for a device that uses perceptual audio encoding to build the data streams that we eventually hear coming from speakers on the other end.
The invention and development of this technology has precipitated a revolution in the way listeners listen to programs and music—and arguably the largest challenge ever faced by radio broadcasters.
Courtesy of the AT&T Archives
17. Nyquist Theorem
In an analog-to-digital conversion, one of the most important considerations is that of the sampling frequency. The Nyquist rate is the sampling frequency; the Nyquist frequency is one half of that. Nyquist in this case refers to Harry Nyquist, a Swedish-born scientist who worked at AT&T between 1917 and 1934. The Nyquist-Shannon sampling theory says that any continuous signal can be completely reconstructed if (during the conversion) it is band limited to one-half of the sampling frequency. At minimum, 15kHz of audio bandwidth would require a sampling rate of 30kHz. A more familiar sampling rate for this audio bandwidth is 32kHz.
Put that together with the invention of PCM in 1937 and you have the foundation for the digital audio revolution that has had such a profound effect on radio, and in turn has created the media that may be radio's ultimate challenge.
16. 33 1/3 rpm record
The development of the 33 1/3 rpm record can be traced back to the beginning of motion picture sound. Western Electric synchronized sound with pictures in 1925 using records that ran at 33 1/3 rpm. After World War II, Columbia Records decided to heavily market the 12" 33 1/3 rpm LP (for long playing). Eventually it became the standard for musical albums and remained that way until CDs became readily and widely available. In 1958, the first stereo albums were introduced using the method invented by Alan Blumlein of EMI in 1931.
15. Regency TR-1
Right before Christmas in 1954, Regency (a division of Industrial Development Engineer Associates of Indianapolis) introduced the TR-1, the first commercially available transistor radio. The design was a four-transistor (parts by Texas Instruments), super-heterodyne configuration. About 100,000 units sold in 14 months of production. Interestingly, if you convert the 1954 price ($49.95) to today's dollars, you come up with a figure that is near to what an Ipod costs now.
Courtesy of Airborne Audio, Lenexa, KS
14. RCA 44
The ribbon-type microphone (also known as the velocity type) was the last of the four basic microphone types to be developed (the other three being carbon, dynamic and condenser). RCA introduced the 44A in 1931, and it was an immediate hit because of its smooth tone and its well-defined directionality. The 44B and 44BX followed in 1936 and 1938 respectively. They became fixtures in everything from movie sets to radio studios.
The low-frequency response of ribbon microphones makes them popular among voice talent. As we all know, jocks like that larger-than-life sound, and it's always an advantage to get it from the mic itself without having to make it up with outboard equipment.
13. Regenerative feedback
Among the early developments in the art of receiver design was regeneration, a design technique in which a particular tuned amplifier is operated with a high amount of positive feedback, thus increasing its gain. Major Armstrong patented this concept in 1914, but Lee de Forest patented it as well in 1916. Thus a contentious, 12-year patent suit began, eventually winding up in the Supreme Court, which ruled in favor of de Forest. Armstrong showed them though; he patented super-regeneration in 1922 and FM later on.
12. Computer Microprocessor
Intel introduced the first microprocessor in 1971. It was invented by Intel Engineers Federico Faggin, Ted Hoff and Stan Mazor. The design was precipitated by a special product order from a Japanese company called Busicom.
Later, Busicom went out of business but Intel had purchased back their design and marketing rights. Thus was born the original: the 4004. At 1/8" by 1/16", and holding about 2300 MOS transistors, it actually had as much computing power as the 1946 ENIAC. Interestingly, the Pioneer 10 spacecraft, launched in 1972, made use of the 4004.
Their functionality has made microprocessors ubiquitous. Still, sometimes I wonder if even the most simple of devices, like a toaster for example, really need a microprocessor.
11. CBS Labs Audimax/Volumax
While it seems that audio processing has been around as long as broadcasting itself, this is not the case. Until the late 1950s “riding gain” on a program was often done manually. This changed when CBS Labs introduced the Audimax in 1959. It was a simple wideband AGC. As FM radio started to come in to its own in the late 1960s, CBS Labs introduced the Volumax, which was an HF limiter. The Audimax and Volumax then worked together as a pair. Some of the last units produced were the 1RU Audimax 4450 and the Volumax 4111. The modern era of audio processing for broadcast had begun.
By the late 1970s, the Max brothers had been displaced by the newest FM audio processor, so many broadcasters today have never used them. Interestingly the processing pair still finds use as special effects processors in recording studios around the country.
10. Tape cartridge
The tape format that became affectionately known as carts was introduced to the NAB in 1959 by Collins Radio. The first mono cart machines were offered shortly thereafter, and stereo cart machines with separate cue tracks were introduced later. Pacific Recorders, Broadcast Electronics, ATC, ITC, Fidelipac, Audicord, Harris, Radio Systems and Ampro all built versions of the technology that became ubiquitous in radio stations. By the mid-1990s, however, computer-based systems had gained enough of a foothold in the playback of music, commercials and other audio messages that many new station builds excluded the cart technology altogether. In the late 1990s the old manufacturers stopped making new machines, and cartridge tapes themselves became expensive: one minute of storage cost more than $5. The days of missed cues, muffled high-frequencies and mono phase cancellation has, for all intents and purposes, finally come to an end. Carts played a major role in radio for 40 years, and the while the technology itself has nearly entirely disappeared, the concept of single-play elements is carried on in its replacement technology.
In 1979, Philips and Sony decided to join forces in the development of a new digital audio medium: the compact audio disc. Philips brought its expertise in video laserdisc technology to the project, whereas Sony contributed its CERC error-correction technology.
The first compact discs and players were introduced in the Asian market in 1982 and reached the United States the following year. This was the beginning of the digital audio revolution. Many listeners heard CDs first played on the radio in 1985.
The first professional CD players were expensive, and the first CD recorders cost stations more than $13,000 in 1994. Early recordable CD media cost $30 per disc.
This entry into portable digital audio storage and playback marked the demise of the analog LP. While the CD is still popular today, it too is being usurped by audio files and portable media players.
8. Satellite distribution
Satellite distribution of TV programs dates back to the early to mid-1960s. The audio portion of the TV program was distributed via subcarriers that were loaded in to the baseband (usually at 6.2MHz and 6.8MHz) above the video signal.
It didn't take too long for someone to figure out that more subcarriers could be added to the baseband to distribute other audio channels. Thus began satellite distribution of audio networks.
Soon thereafter came single channel per carrier (SCPC) distribution. NPR used this in conjunction with audio companding. Other ad-hoc networks were built up as well, many for the purpose of distributing regional programming, such as sports and statewide news networks.
In the early 1980s, satellite distribution of digital audio began with the introduction of the DATS system of non-compressed PCM audio. This was followed by a data-compressed version in the mid-1990s called SEDAT. The Starguide system has practically become the de-facto distribution system of audio networks today, with the exception of the NPR digital SCPC system.
The ease and quality with which network audio could now be disseminated certainly contributed to the success of mass appeal formats and talk radio. To a large degree the state of the industry today can be attributed to it.
7. Electron tube technology
After WWI, two manufacturing groups developed practically all the vacuum tubes of the era: RCA/Westinghouse/General Electric and Bell Telephone. This strong control of the technology of electron tubes relaxed in 1932 when patents began to expire. Companies such as Raytheon, Sylvania, Amperex and Eitel-McCollough soon announced new tube designs.
Through the 1920s and 1930s, as it was discovered by early pioneers in radio technology that higher and higher frequencies could be used for communication, electron-tube designers worked diligently in developing new tubes that could be used to generate power at these ever-increasing frequencies.
WWII spurred rapid development of power tube types, and brought on evolutionary changes that are still in use today: the “beam” tetrode; forced-air cooling; and perhaps the most important (at least for the FM band) the use of cavity type resonant circuits.
The continuing development of electron-tube technology was one of the driving forces in telecommunications from near the turn of the century all the way to the mid-1950s, when junction transistor development started to hit stride.
6. Crystal detector
Early radiotelegraphy made use of spark-gap transmitters; early radiotelephony made use of high-frequency alternators and the newly invented triode tube.
The complementary receiver technology of the time was that of the crystal detector. In the early 1900s researchers discovered that certain substances (such as lead sulfide or silicon) could be used in the detection of radio signals. Greenleaf Whittier Pickard was awarded a patent in November 1906 for the silicon crystal detector. The device itself was simple: a thin piece of wire (sometimes known as a cat's whisker) was put in contact with the crystal. The crystal detector was placed in parallel with a parallel resonant tank circuit that was tuned for the particular frequency the user wanted. A high-impedance crystal transducer was in turn placed in parallel with the crystal detector. The detection of radio waves excited the crystal transducer, which in turn could be heard by the human ear.
Crystal detectors could also be used to demodulate AM. This provided a simple means that the listening public (such as they were at the time) could hear the few nascent broadcast radio transmissions.
Courtesy of CSC Mangement
Major Edwin Howard Armstrong was arguably the most important inventor of the 20th century with respect to radio communications. In addition to his earlier inventions--namely regeneration and superheterodyne--he is credited with the invention of frequency modulation.
He first got FM working in 1933, and showed it to the company that held the most licenses of his earlier inventions, RCA. Even though RCA spent a considerable amount of time and effort evaluating the methodology of FM during the 1930s, ultimately it decided not to license it.
Undeterred, Armstrong went ahead and licensed the invention to smaller companies. He designed an entire transmission system from end-to-end -- transmitter, antenna and receiver--and worked with the fledgling Yankee Network in New England to prove the technology. On Jan. 5, 1940, a special broadcast test was carried out on the Yankee network. The test originated at W2XCR in Yonkers, NY. It was picked up by W2XMN at Alpine, NJ, rebroadcast and picked up by W1XPW at Meriden, CT. It was picked up again by W1XOJ at Paxton, MA, and then finally ended at W1XOY at Mt. Washington, NH. "This test is most gratifying," Armstrong was quoted as saying.
Boston observers report that the program went in to that city with a tonal quality never heard before, and the operators atop Mount Washington reported it as clear as if it were next door. The broadcast went from Yonkers to Mount Washington without using an inch of wire.
Armstrong lobbied the FCC to set aside a segment of spectrum for FM radio (44MHz to 50MHz) and some stations (such as those in the Yankee Network) began broadcasting. During World War II, Armstrong was distracted by the war effort. Everyone used FM during the war, and Armstrong allowed the military to use his patents royalty-free, a gesture that he was not really able to afford. After the war, the FCC moved the FM band to the 88MHz to 108MHz spectrum where it lives today.
Lee de Forest was awarded more than 180 patents during his lifetime, but he is best known for what he called the audion--better known to us today as the triode. This vacuum tube device, an offshoot and improvement on John Fleming's two-element vacuum tube diode patented in 1905, was the first successful electronic amplifier and the genesis of today's electronics and telecommunications industries.
In 1910, while working for the Federal Telegraph Company in Palo Alto, CA, de Forest was able to make the triode perform as an amplifier and sold it to the company for use in long distance telephony.
In 1912 de Forest learned that he could cascade the triode amplifiers, thus creating a system that had far greater sensitivity than had hitherto been available for radio receivers. This, of course, was an essential technological development for the fledgling radio and telephony industries.
By 1916 de Forest had learned to use triodes as oscillator tubes, thus generating substantial amounts of RF current for use in transmission.
That triode tubes are one of the most essential elements in early broadcast technology is unquestionable. They were used for everything from mic preamps, to program amps in consoles, to oscillator tubes, modulator tubes and amplifier tubes in the early broadcast transmitters. Many of us still have the pleasure of using them today.
Courtesy AT&T Archives
It is generally accepted that the transistor was invented at Bell Labs in 1947 (announced in 1948 after patents were applied for and the military was informed) by William Shockley, John Bardeen and Walter Brattain. Though a study of the prior art may cause the claim to be dubious, the fact is that the three shared the Nobel Prize for physics in 1956.
In 1951, Bell Labs made another announcement: the invention of the junction-type transistor, the ancestor to what we are familiar with today.
The properties of the junction transistor--small size, long life expectancy and no need for a filament--overcame many limitations of vacuum tubes. Western Electric (parent of Bell Labs) actively promoted the new technology and licensed the manufacturing rights to more than 30 companies--at $25,000 each--in 1952. This new invention allowed for the early replacement of tubes in two common electronic devices: the hearing aid and the one that we are so concerned with, the portable radio.
The first commercial all-transistor portable radio, the Regency TR-1, came out in time for Christmas in 1954. Although it didn't sell that well at first, the idea caught on with other manufacturers, and by 1957 almost five million portable radios had been sold by the likes of Admiral, Arvin, Emerson, GE, Raytheon, RCA, Westinghouse and Zenith.
The invention of the junction transistor precipitated the invention of the integrated circuit and later the microprocessor, devices around which nearly all broadcast equipment is designed and built today.
2. Electrically recorded records
In 1925 Henry C. Harrison of Western Electric's Bell Labs developed a new electrical recording system for 78 rpm records. Using condenser mics and vacuum tube amps (obviously an early proponent of high audio quality) he obtained a frequency response from about 50Hz out to 6kHz--far superior to the 250Hz to 2.5kHz response of the acoustical recording systems that were in use prior to that time.
By 1930 most record companies had adopted the electrical recording system, and during the 1930s many radio stations gained the equipment and ability to make these transcription discs themselves. Radio advertisers soon discovered that they could prerecord their ads, so that they could be played over and over on the air.
NBC allowed its affiliates to make and use these transcription discs on May 1, 1932. In 1935 the new acetate disc was introduced, and on Jan. 1, 1936, NBC announced the formation of its Reference Recording division. CBS acquired similar equipment in 1938, as did ABC when it was split from NBC in 1940.
Radio stations were perhaps the most fervent users of the transcription disc recording technology. The ability to play material back at a later time, or time and time again was obviously an operational advantage.
In the pages of Radio magazine, and indeed most other texts regarding technologies used for the transmission of broadcast signals, there is little emphasis on the actual receivers used by the listening audience. Still the case could be made that, no matter how good and sophisticated the transmission technology is, it all would be for naught if it were not for complementary receiver technology. While there were many innovations in the art of receiver design during the 1900s, perhaps no single one was as important as superheterodyne principle.
First, it is necessary to go back to the early 1920s to review a little about the AM broadcast receiver technology that was in use. A typical receiver (known as a TRF-for tuned radio frequency) consisted of a chain of tuned circuit/RF amplifier combinations that terminated in the detector stage. The detected audio from that stage was used to drive a loudspeaker amplifier.
This type of receiver architecture has several major flaws. First, the bandwidth of the tuned circuits (for a given Q) is proportional to the operating frequency. Therefore, as the user tunes up the dial, the selectivity of the receiver diminishes.
Secondly, the sensitivity of the TRF varies with frequency; it gets lower as the receive frequency goes lower.
In response to this problem, Edwin Howard Armstrong developed a new idea that he subsequently patented in 1917. Instead of trying to build the gain and selectivity over a range of frequencies (such as the entire AM broadcast band) he converted the varying input frequency to a fixed frequency--known as the or intermediate frequency (IF). The conversion takes place by mixing (or heterodyning) two signals--the signal trying to be received--and another known as the local oscillator. The arithmetic difference in frequency between the local oscillator and the signal being received is always the same (the IF). The IF amplifier is then designed with the appropriate selectivity and gain, thus eliminating the frequency-variable factors of the TRF receiver. What you had then was a better receiver providing a better experience to those that tune in to AM radio--and the ushering in of a new era in broadcast.