On the science side of things "radiophysics" is the study of certain kinds of radiation, propagation, emission, and how it reacts with other matter. Engineers have been using radio waves to work for humankind for over 120 years. Some engineers have a special talent for understanding radio wave behavior. There are many interesting jobs in this field if you find you have a knack in this area.

If you want to learn the basics of how radios work start with the science, learn about radio physics here.

Another good resource for understanding radio frequency design and science is at Circuit Design, Inc.

1.) Radio history
1.a) 1900-1920s
1.a.1) Technical Developments
1.a.2) Schenectady Developments
1.a.3) Voice Radio
1.b) 1920-1950
1.b.1) Amateur Radio
1.c) 1950-2000
1.c.1) Microwave Transmission
2.) Photos of old radios at the Edison

1.) Radio History

Here is a relatively concise history of radio technology. This is a very large subject so we have provided links in each section for further study.

Pre-1900 History

Radio describes the wireless transmission of voice or other man-made signals. The roots of modern radio are found in the telegraph and telephone business, and the roots of those industries lay in the electromagnetics work by Joseph Henry and Michael Faraday. Just a few years later Samuel F.B. Morse and Alfred Vail developed the telegraph.

See the full background of the telegraph here >

Important figures of the pre 1900 period include Edouard Branly, Heinrich Hertz, Alexander Popov and Guglielmo Marconi.

The commercial development of radio began with the development of Marconi's coherer (which was not the first coherer). Although there has been much controversy over Nikola Tesla's claim on early radio much of this is legal posturing/ego and the reality is that a number of pioneers contributed to radio. If we have to pick one name as the 'father of radio' that would be Marconi. Unlike other pioneers of radio components Marconi stuck with radio and pursued the development (and business control) over the long term.

Read about the coherer here >

Below: Edison Tech Center interview with Dr. Pier Abetti, he explains the very basic principle of how the coherer works:

1.a) 1900-1920s Period

This era was quite an exciting time as pioneers of radio raged forth in competition to develop long distance transmission and voice transmission.

Pioneers of Radio:

Ernst F.W. Alexanderson
- pioneer in wireless and TV transmission

Ernst Julius Berg
- developed two way wireless audio communication. Worked on AC power.

Lee De Forest
- Invented the vacuum tube, triode & audion. Improved wireless communication.

Albert Hull
- invented the magnetron (radar) and advanced vacuum tubes (used in many applications)

CW Rice
- developed the loudspeaker, early radar, and other technologies

Nikola Tesla
- improved upon many technologies, most notably AC power.

Important pioneers of radio in this era include Ernst Alexanderson, Nikola Tesla, H.C. Dunwoody, G.W. Pickard and Reginald Fessenden.

Note that during this period wired telegraph lines were still in widespread use and had been technically integrated with telephone systems although Western Union (telegraphy) and AT&T (Telephone) remained separate financially in order to avoid anti-trust problems.

1.a.1) Technical Developments

Early engineers worked to improve radio in the following ways:

Transmit longer distances
Understand the Earth's magnetic and meteorologic effects on radio
Refine the transmission frequency
Refine radio wave detection methods
Developing quality audio transmission

Important early radio components
Each of these components has a fascinating history, to learn more about them just follow the links.
The Coherer
Spark-gap transmitter
Hot Wire Barretter
Electrolytic Detector
Crystal Detectors (1906 and later)
The Alexanderson Alternator Amplidyne (a type of amplifier) Vacuum Tubes:
Audion (triode) Tube
Thermionic Diode
Magnetron (microwave/radar frequencies)

1.a.2) Schenectady Developments

Schenectady, New York was the headquarters of General Electric in the early 20th century. As a result this relatively small city separated from the chaotic scene down in the city of New York became a quiet testing ground for many advanced technologies. Many of the world's best engineers immigrated to the US and took jobs at General Electric. Perhaps the most important of all was Swedish engineer Ernst Alexanderson.

Early Radio Stations at Union College
Union College in Schenectady was a premier place for the study of electrical engineering in the 20th century. Student radio began there in 1910. The first "wireless telegraph" was set up there by Howard Olwin Thorne and Gustave Huthsteiner. They created a 180 ft. high antenna pole. It had an antenna 225 ft. long and 15 feet wide.

In 1916 a radio shack was built on the side of the Electrical Engineering Building. It was registered with the Radio Association of America. In 1917 it was shut down due to the war but resumed in 1919. The call letters were 2YU. It had the call letters 2XQ for experimental work and 2ADD in 1920. Wendell King was the chief engineer.

1919 - Formation of RCA

The U.S. Navy initiated efforts during World War 1 to keep vital radio patents in the hands of U.S. companies alone. They saw this as a matter of national security. General Electric owned the patents of Ernst F. Alexanderson, who until that point was the only engineer to create long distance voice transmission. The Radio Corporation of America was formed in 1919 as a collaboration of technology between General Electric, Western Electric, Westinghouse, United Fruit Company, and AT&T.

1.a.3) Voice Radio

Timeline of the first regular voice broadcasts:

August 20, 1920 - Detroit: 8MK owned by the Detroit News (now WWJ) began regular nightly broadcasts
October 14, 1920
- Union College, Schenectady: 2ADD used a 150 watt transmitter and played photographs into a microphone. It was heard as far away as Hartford, CT. The club promised to air music every Thursday night for the rest of the academic year. They did, H.S. Barney department store lend the records for broadcasts in return for mention on the air.
November 2, 1920 - Pittsburgh: KDKA makes its first regular broadcasts. KDKA is owned by Westinghouse.

February 20, 1922 - Schenectady: WGY, owned by General Electric goes on the air.

Source: the book "Encyclopedia of Union College History" by Wayne Somers 2003

We recommend you read our page on Ernst F. Alexanderson.
Ernst Alexanderson and Dr.W.R.G.Baker developed equipment for WGY. WGY became an experimental lab for Alexanderson.

Significant improvements in radio transmission were made by Irving Langmuir with his pliotron tube.
We also recommend you also read about Albert W. Hull. Hull worked on high frequency radio, and created the magnetron. The magnetron allowed for transmission at microwave frequencies and lead to radar.

The Loudspeaker

While magnetically driven coil speakers had been attempted for some time the development of a modern loudspeaker did not come about until C.W. Rice's prototype in 1921. The challenges which had stopped earlier developers included amplifying electronics and high level understanding of acoustics in the actual speaker materials. The world of acoustics and radio are connected, C.W. Rice not only worked on the loud speaker, but other forms and uses of radio waves including ship and airplane navigation.

Right: The first commercially sold amplifier (first "home-stereo"). It sold for $250 in 1926 (about $3000 in today's currency). This amplifier and speaker system was the first to not require a 'horn'. This Radiola Loudspeaker Model 104 could be hooked up to radios and radio broadcasts could be heard by crowds in public places. Today this type of speaker is used in all radios. Recently speakers have gotten smaller thanks to use of magnetically dense rare-earth materials Learn more about speakers on our page here >

1.b) 1920-1950

The commercial success voice radio spurred research and further technical developments.

Edwin Armstrong was one of the most important radio engineers in history. He developed FM (frequency modulation) radio transmission as well as other apparatus before that. One of the prominent rivalries in engineering history occurred when Armstrong fought David Sarnof in the war over FM technology. This war raged from the 1930s until 1954. Armstrong never lived to see the great success of his invention.
Learn about Edwin H. Armstrong >

We talk about the corporate environment during the formation of RCA in our documentary: Wizards of Schenectady, The Rice Legacy. In this documentary we also show C.W. Rice and E.W. Kellogg's invention of the first amplified loudspeaker, something which revolutionized not only sound film, but radio. See the link to the left to learn more.

1.b.1) Amateur Radio

Amateur Radio has played an important part in the history of radio. All of the pioneers of radio in the 20th century were radio hobbists. Amateur radio provided an outlet in which they could develop skills and test equipment outside of work pressures. Amateur radio operators are issued a license by the country in which they live and follow guidelines on etiquette. They are assigned a 'call sign' which they must use to identify themselves online. If you have an interest in tinkering with radio technology we recommend you go the ARRL website and learn more >

Below is a passage the Schenectady Amateur Radio Association. Many of SARA's members included notable GE pioneers over the years. Wherever you find major workplaces for radio engineers you will find strong local amateur radio clubs.

SARA HISTORY - April 1930
From the Schenectady Union Star newspaper Saturday April 5, 1930

"The monthly meeting of the Schenectady Amateur Radio Association will be held at the YMCA Monday at 8 P.M.
A feature of the meeting will be a talk by Maurice L. Prescott of General Electric Company an authority on shortwave propagation.
The talk is titled "Amateur Waves and How to Use Them." and will be a non-technical discussion covering wave assignments available for amateur use, how to choose the proper wave, and when to use it.
A short business session and a surprise program will complete the meeting. All interested amateur radio (operators) are invited."
It should be noted that this SARA meeting announcement was located right next to the newspaper's radio program listings for the premiere radio station of the region WGY, who produced most of their own programming live in those days. Radio program listings on that particular Saturday included several live dramas, a how-to-do-it show on "building codes", a string trio music program and major live music shows such as the "General Electric Symphony Orchestra" at 9 pm and a local remote broadcast of Saturday night dancing music from the Hotel Ten Eyck from 11 pm to midnight. Oh and right above the SARA meeting announcement is a article stating "17 in Troy Brewery Case Plead Not Guilty" which of course was about arrests made by prohibition officers during a raid on the Fitzgerald Brothers brewery in Troy the summer before. It should be explained to those who may not be aware of the history, that all drinking, manufacturing and sale of alcoholic beverages was illegal due to Federal Prohibition at that time, something that was eventually repealed. Elsewhere in the paper there are several large ads for Atwater Kent radios including one from the H.S. Barney department store on lower State Street for the Atwater Kent Model 1055 for the price of $121.00 "less tubes". That was a lot of money and would come to better than half a months salary for most families back then. The Schenectady Union Star and the competing Schenectady Gazette were one of the two major newspapers in Schenectady of that era. Times were certainly different in 1930!

This article was written by Daniel W. Whelan, call sign WB2WHD, N2UD


1.c) 1950-2000

The latter half of the 20th century saw the continued growth and refinement of radio technology. Radio became vital to automatic control engineering. Below are some of our pages on this technology:

Remote Control
Control Engineering
Rocket Guidance

General Electric Pioneers:

Roy E. Anderson at General Electric conducted experiments in space communication. His first work was in listening for Sputnik in 1956. In the 1960's he worked in an effort to transmit live television images from the Apollo space craft. He pioneered satellite navigation systems before GPS.

See the video below to learn about his experiments:

1.c.1) Microwave Transmission

Microwave transmission describes radio transmission of less than 30 centimeters. Generally long radio waves are better for long distance earth-surface transmission (100s or 1000s of km), microwave energy transmission in contrast requires line-of-sight transmission and has certain advantages. Microwave transmission is good for point-to-point wireless connections. It is vital for communications with satellites.

Microwave transmission is the basis for many technologies including doppler radar, defense department radar, backup navigation systems for ships and aircraft and certain types of remote controlled aircraft. Microwave technology is vital for communications, mountain-top microwave towers form 'trunks' which transmit television and voice communications to local distributors.

How it Works:
Most microwaves are generated using a cavity magnetron. Electrons are emitted from a hot cathode and spin around cavities. Resonation happens and this amplifies the signal to microwave frequencies.

See our page on the Microwave Oven which has the video on the workings of a magnetron.

Klystrons Video: How a klystron tube works, klystrons were used to generate radio waves in powerful radar systems as well as TV transmission:


2.) Photos of radios in the Edison Tech Center collection:

Here are just a few photos of some of the radios on display at the Edison. We have hundreds more in storage and they are displayed at times or can be used by teachers for classes held at the Edison.

Left and above: Peerless Reproducer Radio

Below: radio with original batteries (wrapped in plastic) and extra tubes (in boxes)

Related Topics:

Vacuum Tubes

The Microwave Oven

Lightning and Surge Arrestors

Remote/Radio Control


More Stuff

Smithsonian Institute
Schenectady Amateur Radio Association
Wizards of Schenectady, The Rice Legacy. 2011. Edison Tech Center
Interview with Rudy Dehn. 2013. Edison Tech Center
Techsplorer - Roy E. Anderson. 2008. Edison Tech Center
Techsplorer - Pier A. Abetti. 2008. Edison Tech Center

Edison Tech Center

For use of Edison Tech Center images and videos see our licensing agreement.