e would be remiss as an antenna magazine if we didn’t include reference to Dr. Hidetsugu Yagi (1886 ~ 1976) whose contributions have had an enormous effect on the lives of so many people around the globe for so many years. It’s almost impossible to crack open a radio or antenna-related journal and not see the word (name) "Yagi". Most folks, at least those not involved in radio, would be surprised to know that those funny-looking multi-element TV antennas sticking up above their roof lines were originated from a concept and invention of Dr. Yagi’s. Now that’s a lot of antennas without regard to the endless variations of amateur radio antennas in that same name. But, even some may be surprised to know that Dr. Yagi was focused on the dielectric technology more than 50 years ago! In this month’s issue of antenneX for August 1999, we have an interesting story for you as brought to us from personal experiences by Stanley Whiteman, W1MDZ.

The development of Japanese power industry started with the foundation of Tokyo Electric Lamp Company in 1883. In the following several years, the same kind of companies were also founded in Kobe, Kyoto, Osaka and other Japanese centers. Early system of transmission and distribution of electric power in Japan, as in America, was in essence Edison's DC system. But, after that as the demands for electric power increased, the spread of using a high-tension alternator has begun. At the same time, Tokyo Electric Lamp Company bought the alternator made in Germany. Osaka Electric Lamp Company, in the western part of Japan bought an alternator made by General Electric Company. The alternator license General Electric Company bought from the Westinghouse Company was the one which Tesla had sold to the Westinghouse Company, thus, this important invention originated with Tesla and led later to significant contributions in the field of Japanese communications technology.

One of our readers, Karl, DJ5IL, reports this additional background on Tesla: "He was born on July 10, 1856 in Smiljan, a small village in Croatia. He studied in Graz (Austria) and Prag (Czech Republik) and later went to America. On June 6, 1884 he arrived in New York with only a few cents in his pocket. In March 1885, the Tesla Electric Light and Manufacturing Company was founded. Tesla was a real genious and made many inventions. On February 8, 1943, he died in his Room in the Hotel "New Yorker", where he lived for his last 10 years."

Before the War between Japan and Russia, considering the pending need of military ships for wireless communications, the Japanese Navy had set up the Wireless Researching Committee in 1900. Soon after that, in 1902, Professor Shunkichi Kimura from the Japanese Naval College went to Europe and America together with a naval officer to investigate the wireless technology. Professor Kimura, who had already had some experiences from America, read Tesla's book about HF alternating current. He then asked Tesla to explain more about the wireless concept and visited Tesla's laboratory in Manhattan, USA. Tesla was 45 then and he had already started building The World Broadcasting Tower at Wardenclyffe in Long Island, USA and made the first step of realizing the dreamed-about "World System".

As reported, Tesla performed a fascinating demonstration of a giant Tesla coil for Kimura. Comparing to power transmission without wire, purportedly Tesla said that the wireless telegraphy was not at all such a great invention and rather put down the potential. Kimura wrote an essay about that event which stated: "After my visiting Tesla's laboratory and seeing the demonstration of his giant coil, it could be described as a giant snake winding all around. That experience of demonstration made me understand the efficiency of the electrical resonance at once. Sneering at the wireless communication as a great invention, Tesla said that he realized the meaning of the wireless transmission of power and wireless electrical lighting. Maybe that would be realized sometimes in the future, but for the present moment it is not useful for our research". It has been observed that Tesla's low opinion about the importance of the wireless telegraphy had something to do with personal envy of Marconi's recognition for the wireless over Tesla’s early achievements in this field.

However that may be, through this research, Kimura was convinced that their (Japan’s) technical attainment of wireless telegraphy was by no means inferior to that of the West. So, after returning to Japan, he tried to develop a unique Japanese system of his own. The result of this effort was to equip the patrol ship "Mikasa" with a wireless machine before the battle at the Japan Sea where "Mikasa" used it for transmitting information about the Russian Battle Fleet.

Now, enter Dr. Yagi. Kimura's successor in relationship with Tesla was a Japanese scientist Hidetsugu Yagi. He was a famous inventor of the television antenna who respected Tesla's work and it was Yagi who presented a paper on Tesla's power transmission without wire at an International scientific society in Japan. He was also known as a pioneer in the field of radio control in Japan, and respected Tesla's efforts also in that regard. So, now what about a "Yagi" antenna?

In his laboratories, beginning in 1924, Professor Yagi and his assistant, Shintaro Uda, designed and constructed a sensitive and highly-directional antenna using closely-coupled parasitic elements. The antenna, which is effective in the higher-frequency ranges, has been important for radar, television, and amateur radio The familiar Yagi TV antenna is a Yagi-Uda array, named after these two Japanese electrical engineers: Hidetsugu Yagi, who invented it in 1928, and Shintaro Uda, who perfected it for television reception in 1954.

Michael Brady of Oslo* goes on to say that "In this sense, array means having many elements, which is exactly what this type of aerial has. The metal grid at one end is a reflector. It focuses intercepted television signals on to the actual aerial in front of it, which is called the driven element, and this part of the array is connected by a cable to your TV. The principle is much the same as that of a silvered reflector at the back of a car headlight, which focuses the light emitted by an electrical lamp in front of it into a beam to light the road ahead.

In front of the driven element, away from the reflector, are several director elements, which are the spines. They sharpen the focus of the aerial in one direction, much as the lens of the car headlight directs the light from its reflector into a particular pattern. For the TV aerial, this pattern resembles a cone, which should be pointed directly at the local TV transmitter to receive signals from it. The rod along the axis of the aerial supports the elements mounted transversely on it and keeps them in their correct places, much as the frame around the car headlight holds the reflector and lens together.

The reason why the Yagi-Uda array has proved so successful as a VHF and UHF television receiving aerial is that, for such a small size, its performance is excellent. A similar performance from a parabolic aerial, of the type used to receive satellite television signals, would require a dish many times larger."

Then, Peter Buck of the Physics Department, Exeter College states*: "The surprising thing about the Yagi-Uda array television aerial is that most of it is not connected to the television at all. The only part that is linked to the receiver, via the coaxial cable, is the single pair of spines which comprise the dipole and lie immediately in front of the small metal grid or reflector.

The length of the dipole itself needs to be about half a wavelength in order to receive the television signal, but on its own it would be too weak in most areas. The reflector is a quarter of a wavelength behind the dipole, and adds significantly to the gain--or strength--of the aerial. All the other spines, known as directors, are in front of the dipole and they, too, are a quarter of a wavelength apart and half a wavelength long. Their job is to increase the gain of the aerial--so the weaker the signal, the more are needed.

There is a price to pay for this increased gain, and that is the directional properties of the aerial. A short aerial with few directors in an area close to a transmitter needs little care in aligning it, but a large aerial that is carrying the many directors necessary in areas with a weak signal, needs to be aimed very carefully at the local transmitter.

Terrestrial television transmission is ultra high frequency (UHF), which has a short wavelength, so the half-wave dipoles are short. FM radio is very high frequency (VHF) which has a longer wavelength, so the half-wave dipole needs to be longer. So, even though some FM radio aerials are similar in design, they need to be much larger.

Some television aerials have their spines, known as elements, in a horizontal plane--this means that the local transmitter is using horizontal polarization, while a vertically aligned aerial means that the transmitter is using a vertically polarized signal.

This arrangement helps TV watchers to avoid interference between transmitters which are located close together. FM radio transmission uses mixed polarization (horizontal and vertical) because many of the listeners are mobile, using portable radios or radios in cars, and are unable to maintain regular alignment of the aerial."

NOW HEAR THIS!
In this month’s issue, we are pleased to present this story of Stan and Dr. Yagi, our first full article in streaming audio! Hear this interesting story as told by Stan, W1MDZ in his own words by recording from his home in Danforth, Maine. I hope most of our readers now have sound cards and speakers attached to their computers as we would like to present more "live" articles in this manner, even video at some point. If you have audio and have the Windows 98 version of RealPlayer installed, you will still need to upgrade to RealPlayer G2. It’s free software for download and can be found at http://www.realplayer.com. Or, go here directly to the download page: http://www.real.com/products/player/downloadrealplayer.html?wp=dl0699&src=hp_butn,990706home_1&lang=en

They have a RealPlayer G2 Plus version too but it’s not free. Just follow the "Free Download" links. Those familiar with streaming audio know it is a web technology that allows you to listen to the file while its being downloaded, rather than a wave sound file that has to be downloaded entirely before playing. Plus, the RealPlayer sound file is only about 10% the size of a wave file. Even so, an entire article recording such as this one is about 3MB! BUT, it would be about 30MB in wave form making it unsuitable from practical use on the web.

If you want a quick test to see if your audio device is ready, try my streaming audio announcement and introduction of this article which has a link on the front cover, top right hand location. OR, just click right here"

CLICK TO LISTEN (or Test)

Plus, you can record to keep the article as the audio plays!
Just launch your sound recorder & be sure to have correct input/output selected,
OR, record to your tape recorder using the "line out" jack on the sound card.

But, for those of you who are "audio challenged" we haven’t forgotten you either. For you, we have a text version along with the diagrams of Dr. Yagi’s and Stan’s antenna concepts. However, I urge you to consider upgrading your computer so you won’t miss out on this exciting new feature we offer of a "talking magazine!" For about $50-$60 US$, you can add a sound card and speakers. The prices have really dropped on many such devices—so you can’t afford not to join in the fun! We hope to bring many more articles to life in the very words of its author. What a great innovation for posterity! Wouldn’t it be a thrill to hear the words in the actual voice of Marconi?