MAK's Radio History Page
2004 All rights reserved, Updated Apr 29, 2004

Welcome to the "Radio MAK" old radio pages. While photos on these pages primarily emphasize radios of the 1920s, this summarized history page is intended to provide context of overall radio development.
(Note this page is a draft version under review to confirm content; the reader should therefore consider the possibility of factual errors on this page...)

In 1865, James Clark Maxwell theorized electromagnetic (radio) waves. The first well-documented experimental evidence of electromagnetic waves was by Hertz in 1888. However, some likelihood exists that David Hughes (professor of music, University of KY) may have successfully generated and detected electromagnetic waves in 1879. Also, Sir Oliver Lodge was developing experimental devices in the same timeframe as Hertz. While the efforts of Maxwell and Hertz were successful from the standpoint of theoretical and experimental physics, they did not pursue practical applications of radio. Nor did Lodge at that time, although in later years he did become involved with a wireless company.

Very Early Technology
The technology used by Hertz was spark gaps for both the transmitter and receiver. A spark gap produces a broad spectrum of radio frequencies, which may be radiated through coupling to an antenna (which could potentially be part of the spark gap apparatus itself). The antenna can also provide some incidental tuning, where additional tuned circuits may or may not also be applied. The need for tuning (transmitter and receiver circuits resonant at the same frequency) became explicitly understood through the work of Lodge, with his 1897 tuning patent. A receiver using a spark gap depends on visual observation of the small spark that can be generated from radio signals coupled into the receiving equipment. The spark gap remained the only practical transmitter technology in the early 1900s. The continuous arc transmitter in 1904 provided a signal of better purity than the broadband spark, and also allowed initial experiments with transmission of voice.

Receiver detector technology advanced from the spark gap to the coherer, invented (or at least perfected) by Branley, in the 1889-90 timeframe. (Lodge also performed some work in developing coherers.) The coherer consists of metal filings in an insulated tubular container, with electrodes at each end. The electrodes are connected to a circuit that is activated when the coherer conducts. Loose metal filings in the coherer normally do not conduct well, but will do so when radio signals are coupled into the circuit, causing the filings to "cohere" together. The coherer is reset to the non-conducting state by a tapper activated by the detector circuit. An additional receiver-related invention of the time was the electrolytic detector, developed in the 1900-03 timeframe.

Note that while we often associate vacuum tubes with early radio equipment, this technology would not be invented and applied to radio until 1905.

Initial Applications
By the mid 1890s, the application of radio waves to communications was within the vision of innovators, with the most successful example being Guglielmo Marconi. (Note that Marconi was more a business visionary and innovator than a fundamental inventor.) By 1901, the relatively crude technology of coherer detectors and spark transmitters allowed Marconi to span the Atlantic. Marconi obtained essentially a monopoly on commercial ship-to-shore communications in the 1901-08 timeframe. Transmission was via "Morse code" at that time, not voice.

In addition to commercial communications, e.g., ship-to-shore, other users of radio waves at the time were experimenters and the amateur radio operators of the day. Initially, use of radio frequencies was essentially unrestricted. It was not until 1912 that amateurs were limited to specific frequency limitations, restricted to frequencies of 1500 KHz and higher, considered all but useless in that time period. The concept of radio broadcasting as we know it today was not yet in place.

Further Technology Development
Significant technology development occurred in the first two decades of the twentieth century, encompassing both devices and radio circuitry.

The diode vacuum tube was invented by Fleming in 1904. This provided a stable detector of radio signals, though with the obvious disadvantage of requiring filament power. The crystal detector (i.e., as we think of in a "crystal set" radio) was perfected in 1905-06. The triode vacuum tube was invented by DeForest in 1906. (DeForest, incidentally, was a native of Iowa, born in Council Bluffs in 1873.) The triode was significant in that it could amplify as well as serve as a detector. With amplification, the amount of signal power available for observation was no longer limited by the small fraction of the transmitter power intercepted by the receive antenna. However, gains of early triodes were rather modest. Further, tubes were relatively expensive and required power for operation, typically supplied by a number of batteries, so their use remained limited.

Radio receiver circuitry used increasingly effective tuned circuits ahead of the detector to differentiate among signals of different frequencies. A typical receiver may use one tube, crystal detector, etc., but multiple tube receivers were initially too expensive for common use. A breakthrough occurred with E. H. Armstrong's regenerative circuit invented in 1912 and patented in 1914. (It is notable that others were pursuing similar developments at essentially the same time. This leaves the invention of regeneration a bit murky at best. However, given Armstrong's numerous significant advances to the development of radio, it seems quite appropriate that he be given major credit for regeneration.) The regenerative circuit used positive feedback to reintroduce some of a tube's amplified output to contribute to the input of the tube circuit. This greatly increased the effective gain of the circuit far beyond that otherwise available from a single tube, though at the expense of instability that required careful adjustment of the receiver. This invention allowed a reasonably high performance radio to be constructed using only a single tube. (Note that the regenerative circuit should not be confused with the superregenerative circuit variation that Armstrong later invented.) The regenerative circuit also provided the basis for the electronic oscillator, allowing more sophisticated, spectrally pure, transmitters to replace the earlier spark and arc transmitters.

Armstrong also invented the superheterodyne circuit during his WWI service. The superheterodyne is the basis for all modern radio receivers, though the number of tubes required for practical implementations prevented it from monopolizing receiver designs for several years after its invention. (At the risk of skipping too far ahead, E. H. Armstrong was also the inventor of FM in 1933.)

Aside from the regenerative and superheterodyne circuits, another straightforward design concept of cascaded amplification stages became increasingly practical as tube costs declined, e.g., in the mid 1920s. For example, a receiver may consist of a couple of stages of tuned circuit followed by triode amplifier. These stages may then be followed by a detector, and then a couple of stages of triode audio amplifiers. Variations on the design included neutralization of the radio frequency amplifier states to maintain stability as gain was maximized. Such a receiver was easier to operate than a regenerative, though at the expense of a number of tubes and the batteries to power them. The ability to operate tube circuits from household AC power did not occur until the mid to late 1920s.

Expanding Applications
Until 1920, radio was the domain of commercial operators and amateur experimenters. During WWI, the value of radio to the military was recognized. Spin-offs of military use included advancements in circuitry development (e.g., superheterodyne), as well as manufacturing technology, leading to more affordable vacuum tubes.

Although some experimenters dabbled in broadcasting, the start of broadcasting is generally attributed to the 1920 efforts of Pittsburgh's Frank Conrad, 8XK; this station became KDKA. A sufficient number of experimenters had receivers capable of receiving the 8XK broadcasts to constitute a sufficient audience to maintain interest in broadcasting. Existing manufacturers of sets for amateurs suddenly found a greatly expanded market. And construction articles were extensively published (e.g., in magazines and even in daily newspapers) allowing "do-it-yourselfers" to build receivers. So popular was do-it-yourself construction that home-made radios exceeded commercially produced sets until the mid '20s.

Initially, only two frequencies were allocated to broadcasting, one for normal operation and the other for weather/farm reports. Competing stations were forced to share the same frequency; this worked more harmoniously in some areas than others. Within a few years, frequencies were expanded to include a large part of our current AM broadcast band. This was effective at allowing more stations to coexist, though it carried the implication that radio receivers now needed to accommodate the frequency range, and needed adequate selectively to effectively tune in one station while suppressing others.

Receiver Evolution
Prior to the beginning of broadcasting in 1920, typical receiver designs in use featured one triode in a regenerative detector circuit. Other circuits, including low-cost crystal sets, were also in use. Headphones were typically used to listen to the limited audio power levels produced by the single tube. These receiver designs continued to be popular as increasing members of the public began listening to radio broadcasts. Audio amplifiers were available as accessories to boost audio levels to drive a horn speaker, and more sophisticated radios with integrated audio amplifier stages became popular. The instability inherent in the regenerative design presented problems; in fact, less sophisticated users could misadjust the sets such that they effectively became low-power transmitters of interfering signals. This interfered with neighbors' radios as well as their own.

Designs employing cascaded amplification stages began to replace regenerative sets for everyday radio users. Regenerative sets remained popular among more sophisticated users who could extract greatest performance from some multi-tube designs, and also among most cost-sensitive users wanting to get the most out of a single tube. By the mid 1920s, "three dialer" receivers were quite common, using two tuned radio frequency amplifier stages followed by a tuned detector circuit, followed by typically two audio amplifier stages. This design approach is readily apparent in the Atwater Kent model 10c. These 5-tube receivers were expensive, on the order of $100, representing a considerable amount in those days. Availability of tubes requiring 1/4 amp of filament current instead of the previous 1 amp helped make these multi-tube sets more practical to operate, though the 6V automotive battery used for filament power still required frequent recharging. The three tuning dial configuration of these receivers was necessitated by the poor tracking of stages that required separate adjustment of each tuned circuit. This delayed the obviously more desirable approach of a mechanically coupled arrangement where a single tuning control operated multiple stages. Improvements were developed by the mid to late 1920s to allow such mechanical coupling to become practical, and transition sets sometimes included the ability to tune (or incrementally alter) stages individually as well as in a coupled manner.

Superheterodyne sets were commercially available from the mid-20s, where the local oscillator and radio frequency stages were typically tuned separately; again, tracking was somewhat a problem in early designs. It was not until the 1930s that superhets became truly popular. This was aided by development of more sophisticated and cost-effective tubes, along with AC power supplies that helped relieve the operating costs of an extra tube or two. Radios of the early 1930s employing superheterodyne circuitry included many "gothic" or "cathedral" sets (e.g., Atwater Kent model 82) that are so often thought of when one mentions "old radios". However, based upon the perspective gained from review of the above material, one recognizes that such "old radios" are really quite modern when compared to the previously described sets of only a decade or two earlier. The '30s sets were typically AC-operated superheterodynes with single dial tuning, and even included automatic volume control to keep the received volume level more constant as a station's signal faded in and out.

While this page emphasizes older radios, developments more recent than the 1930s deserve at least some mention for completeness. Radios described thusfar that were intended for consumers received the AM broadcast band. In the later 1930s, inclusion of short-wave bands became more common, as world events increased interest in hearing foreign broadcasts. FM was invented by Armstrong in 1933, with initial broadcasts begun in 1938. The original FM broadcast band was in the range of 42-50 MHz; it was moved to the current 88-108 MHz allocation in 1945. The invention of the transistor in 1947 led to the development of the first transistor radio (Regency TR-1) in 1954. Tabletop radios using tubes remained cost competitive into the 1960s. Transistor and integrated circuit radios are of course the dominant technology today, aside from a few experimenters who may still enjoy building a crystal set or tube radio.

Although the development of television warrants a lengthy description of its own, mention should be made of mechanically scanned television that pre-dated electronically scanned television. A means of sequentially transmitting individual parts of a picture was recognized early in television development. An early approach was the use of a scanning disk, where a rapidly spinning disk with a spiral series of holes allowed light from sequential rows of a picture to reach a photodetector, thereby effectively scanning the picture. A similarly rotating disk at the receiver allowed light from a neon tube, modulated by reception of the transmitter's photodetector signal, to reach the viewer's eye. Persistence of vision allowed the viewer to perceive the initial picture. This late 1920s to early 1930s technology was soon overshadowed by electronic television. An example manufacturer was Western Television.

As one may expect, radios pre-dating the beginning of broadcasting are relatively scarce, as the number of commercial users and amateurs and experimenters was quite limited. Receivers from the early 1920s may certainly be found from time to time, though mid-20s sets are more commonly found, e.g., in antique stores, etc. Sets from the 1930s are more commonly seen, and their characteristics of operating from AC power rather than specialized batteries may be more appealing to those wanting to have a set restored to operating condition. A word of warning, however: Components can deteriorate in these sets, making it somewhat dangerous to attempt to operate them unless they have been inspected and possibly restored by someone with knowledge of such radios.

The old radio pages on this website primarily emphasize 1920s radios, with perhaps a few items earlier or later than this period. For one wanting a brief example of developments in the 1920s, the Grebe page may be of interest. It includes sets from 1919 to 1925, including regenerative single tube sets, companion audio amplifiers, and a TRF set that includes a clever clutching arrangement allowing either 3-dial or single dial tuning. Other pages emphasize radios of selected manufacturers, while yet additional pages include artifacts categorized in other manners, such as radios associated with a specific state, a sampling of speakers , etc.

Go to higher level Radio MAK page
Go to Radio MAK