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.
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.
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.
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"
(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
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
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
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