[NLRS] FYI My presentation at eastern VHF conf in Oct.

[Steve Gross-N4PZ]

The Evolution of the Long Yagi
            Professor Hidetsugu Yagi and his graduate student Uda in Japan came up with the idea in the 1920s of adding multiple directors to a small 3 to 4 element beam as we called them when I was licensed in 1956 as WN9OJI. They discovered they could increase gain by doing that. They probably had little understanding of what was happening but that was the beginning.
            In 1956 January QST, an article was published by W6QKI Herb Johnson and W2NLY James Kmosko who worked independently on the same project without any knowledge of the other doing the same thing.
            They used the trial and error approach to experimentally assembly a long string of directors on a boom to produce a very long yagi for that time. A field strength meter was used to measure changes as different element length and spacing were tried. The literature of the time stated that all directors should be the same length. This turned out to be not quite true.
            W8SDJ in southern Ohio built a long yagi with tapered element lengths. Everyone agreed that Claud was nuts but he had one of the loudest signals on 2 meters at my QTH almost 300 miles away. Hmmmm.
            I built my first antenna out of a Popular Mechanics magazine in 1949 at age 10. We had just bought our first 10 inch B&W RCA TV and I wanted to receive channel 12 from Milwaukee 90 miles away.
            A wooden broom stick and wire from a coat hanger was all I needed for material. It seemed to work but who knows.
            Time passed and I got my ham license in 1956. WN9OJI and then W9OJI. In 1957 when I graduated from high school, my mom gave me a 2 meter Gonset Communicator. That was it! The mysterious VHF bug bit and I was never the same although I did still work HF mainly CW since we had no money for AM phone rigs.
            We bought a little house in Wheaton, Illinois so I no longer had to sneak antennas up on the roof of the 3 story apartment building in which we lived since 1945. Yes, I am getting damned old, but my enthusiasm never fades.
            I somehow got a Rhone tower and Sears delivered a 30 foot 3 inch diameter irrigation pipe to our mansion and construction began on my monster yagi. Plans were taken from the VHF Handbook by W6SAI and W6QKI who were the big guns of that time.
            I had no idea what I was doing so I got some perforated metal strap at the hardware store and made the elements from some green copper wire I had salvaged from a train wreck three blocks from our house. Of course I labored for days to remove the green oxide. The wire was soldered to the strap and placed precisely where the VHF handbook indicated. All directors were the same length. I had no idea what boom diameter correction was so I assembled the thing and put it on my shiny new tower.
            I think I fed it with Belden Celluline which was 300 ohm oval nitrogen filled foam TV feedline. I have some 400 feet I picked up a few years ago. Believe it or not, the losses are comparable to one 5/8 inch Heliax but a nightmare to actually use since it’s 300 ohms balanced line.
            My yagi had 3 big lobes off the front. I remember the first side lobe was almost as strong as the main lobe, but with my 7 watts AM it worked. The serious VHF gang almost all used collinears at that time. They all agreed yagis didn’t work.
            Over the coming years I built dozens of yagis using the original information of the time. I spent hours, days, and years in the back yard experimenting. Aluminum clothes lines were straightened out and used for elements.
            Various ideas were tried but I never had any idea what I was doing as a kid. It was all trial and error.
            Then in the 1970s, the F9FT yagi with tapered elements became all the rage with the EME gang. It had tapered elements so I decided to modify the 13 element 24 foot yagi out of the ARRL handbook with tapered directors. We had just moved to Florida and I now spent an entire winter tinkering with the 24 ft handbook yagi. I did succeed in making it work much better.
            I cut the thing into pieces short enough to put on the plane and took it to the CSVHF conference. It beat the F9FT which made the USA representative Joe Marinari absolutely furious. He worked feverishly to get the F9FT up to my piece of trash to no avail. The next year the antenna measuring contest had two categories, commercial and home brew. LOL.
            After the appearance of the F9FT and a brief appearance of the NBS (National Bureau of Standards) designs DL6WU appeared with the answer we had all sought for decades. His design had no limit to the length and one could pick up where he left off and make it longer without going back and tweaking the entire string of directors. There are certain lengths that seem to stall the gain, but it resumes as one adds length.
            K1FO and I spoke for many hours about yagis. Steve taught me what was actually happening to the incoming wave front so that everything in the capture area ended up on the driven element in phase. He referred to it as the “slow wave theory.” K1FO, YU7EF and many other worked with the DL6WU design to modify it to meet their particular requirements but it all started with DL6WU as far as I know. K1FO focused on maximum gain while keeping the first side lobe down to a reasonable level. YU7EF focused on getting the first side lobe down 20 db. His design made it very quiet for EME since it’s not hearing galactic noise from the side lobes. Other people did similar mods to meet their needs.
            Now how does the yagi actually work in simple English without a page full of high mathematics to explain it? Steve explained it this way:
            Picture a flat slice of the approaching wave. As the wave passes over the directors it is slowed down, but progressively less and less as we move away from the boom. It has a longer distance to travel, however. The outer edge is going a bit faster than the inner edge of a piece of the slice which turns or steers the whole slice toward the driven element. We finally get too far away from the boom for the director string to have any significant effect as we move away from the boom. That is the outer edge of the capture area or aperture. That point is ½ the stacking distance. A similar antenna above or next to the first one wants the edge of its capture area to just touch the edge of the second antenna’s capture area. Any metal in the same plane as the elements in the capture area will disturb the speed of the incoming wave. That is why one never stacks two horizontal antennas side-by-side with a metal pipe for support between them. Chances are good that the effect will be two antennas with no gain being supplied by the space between the two yagis therefore in effect you have only the effect of one yagi’s gain. The capture area of a long yagi can be surprisingly large and anything anywhere in that capture area that is metal and in the same plane as the antenna’s elements can and will interfere with the “slow wave structure” thereby reducing performance.
            That’s it without Calculus. Simple huh? Now go ask guys to explain how a yagi works and you can be the genius!

            Onto some miscellaneous things I have learned over the decades:

1)      Look at the advertisements selling yagis for FM vertical polarization. I see them mounted on a vertical pipes with vertical elements. What do you suppose that does to the incoming wave passing that supports the pipe under the yagi?
If you install it on a metal pipe, the lower part of the incoming wave is almost certain to be disturbed and who knows how much performance is lost.

2)      Most of us use through the boom insulated elements. Plastic shoulder washers and stainless steel keepers cost $1.00 USD per element. I have 160 elements on my 4 x 32 foot yagis for 432. Shrink tubing will work just fine if you put two layers on the element and shrink one layer over the other. Hold it in place with hot glue. Some smart SM Swede came up with that one.


3)      Louis Ancio (call unknown) discovered 40 years ago that he was unable to get the gain he expected from an EME array he built out of used aluminum rods until he removed the aluminum oxide with SOS pads or sand paper. I found that as he claimed, my EME array lost about 1 dB in 6 months. Cleaning with SOS (steel wool) pads brought it back up. On echoes it is 2 dB!
This is a good reason to have a tilt over tower.

4)      Here is a secret Bird doesn’t want you to know. In the manuals for the Bird 43 watt meter of 40 years ago, there was a graph showing that all slugs of 500 watts and above are virtually flat frequency-wise from 50 MHz to 1000 MHz! Gigacycle or is it Gigahertz. Don’t go out and buy a 1kW slug for 50, 144, 432, and 1296. One for 144 or 432 will be within 5% accuracy across the entire range. Gee, I wonder why Bird took that information out of their manual? I’m getting too old for that name-changing stuff. Cycle or Hertz.

Keep your mind sharp. Delve into why and how these things we so passionately play with work. Use that brain or lose it. What an amazing and diverse hobby we have….
Those of us who have worked serious EME have left a signal in the universe for all time. It’s damned weak now, but it will be there long after we are gone, zipping away at 186,000 miles per second. Golf can’t do that!

—73 Steve N4PZ