Thursday, August 21, 2014


In America no one remember Roebuck. Sears got all the credit. But Alvah Roebuck was a real person and after Richard Sears bought him out he went on to be the president of the Emerson Typewriter company. Being forgotten has nothing to do with success... it's about who gets to write the history. So it is in this other radio-related case.

The Yagi is a very common very useful high gain antenna. I've installed many myself. It's a directional antenna with one driven element and a number of parasitic elements. The driven element (usually a dipole) is connected to the receiver by a feed line. The parasitic elements are not electrically connected. They act as passive resonators receiving and re-radiating radio waves. These are out of phase with the original wave. This interferes with waves that are also out of phase with the original wave, such as those coming from directions perpendicular to the direction the antenna is pointed. A Yagi may also have a reflector at one end. Which will also cancel out those coming form the opposite direction. A Yagi is more properly known as a Yagi-Uda. More on that in a moment.
A side note on how a Yagi-Uda and Log-Periodic antennas differ. They do look very similar. ALog Periodic antenna consists of many dipole elements along an axis which decrease length. In their case all the elements are driven. However because they are different each is only resonant at a given frequency. And while a Yagi can have wide or narrow beam width a Log Periodic by design is always narrow. They are common in both UHF and VHF bands,and have been since they were in vented in 1955 by  Dwight E. Isbell, Raymond DuHamel  at the University of Illnois. The Yagi-Uda predates it by about three decades. Despite that the names are used interchangeably by some.

The name Yagi comes not from it's inventor Shintaro Uda, but from his collegue Hidetsugu Yagi. Both were employees of Tohoku University. But while Shintaro Uda was a professor and Lab Engineer, Yagi was a professor and the Lab Director. Uda invented the design in 1926. (patent 61195)  Yagi got the credit for a few reasons firstly though that he wrote about it in English. (There is some evidence Uda also wrote an English paper for the IRE) But they had previously published an article together in japan in 1926. But it was Yagi who traveled to America in 1926 and 1928  for talks on the new technology. Yagi also filed the patent in Japan and the US without Uda's name attached. Then the colossal prick sold the US patent to RCA. In 1952 he founded Yagi Antenna Inc which further associated his name with the invention. The IEEE article on the topic kind of smooths over that problem. More here.

Uda wrote some other fundamentally ignored but strong papers in the 1920s "High Angle Radiation of Short Electric Waves" and "On the Wireless Beam of Short Electric Waves" in 1927 then in 1929 "The Practical Short Wave Limit of Triode Vacuum Tube Oscillators."  A collection of his papers was printed in 1928 titled
"On the wireless beam of short electric waves."   In 1954, Uda and Yasuto Mushiake wrote a book on the topic titled The Yagi-Uda Antenna.  Thsi probably mounted the first reclamation of his antenna. Then in 1974 he published "Short wave projector: Historical records of my studies in early days" which was even printed in an English edition. I'd love to read that but it's long out of print. He died in 1976... just a few months after Yagi.