High SUNSPOT numbers...

A few years ago I had a colleague on the QRL working for our service department. He was supporting our FM radio-station those days but somehow, the frequency and transmission mode was out of range for his interest. Today his a professional teacher also known as ON5ZO, Franki. Anyhow, during our breaks, most of our conversations were antenna related. Franki had already converted his parents lot into a NATO like communication HQ and wanted the best GAIN to Footprint antenna. We decided to see what could be done on a 3m

boom with 3 elements. As compromise he wanted the optimum design only for the CW DX part of the 10 meter band.

The same evening I started EZNEC 3.0 and ran some configurations. After some modelling work, I could propose a design to my antenna buddy during our next work "break". Due to his enthousiasm and HAM spirit I soon wanted to see how the model would behave in real world and dimensions. I gathered te needed ALU tubing, nuts, bolts and started the drilling.

Bandwith and VSWR.

Since Bandwith wasn't an issue ( ON5ZO lost his boomset at that time ) The paddle 1.5 VSWR bandwith wasn't going to be more than 150 kHz. I choosed my favorite matching technique, the Beta match ! This design requires a splitted driver-element.

unmatched Impedance 12,53 - j22,2 Ohms.

Delta : SQRT[(Rs/Ra)-1] where Rs = 50 Ohm and Ra = 12,53 Ohm.

Delta = 1,73.

(-Xa) : Delta.Ra = -j21,67 (close enough to -j22,2)

XL : Rs/Delta = j28,91 (Coil or Hairpin across feedpoint)

Mechanical strenght.

A single element will NOT fail in a 150Kph windspeed, this does not mean that the whole YAGI will survive such winds. However since element to boom clamps are locked with 4 poprivets each and fastened with M8 nylock bolts it should be possible to challenge the highest windspeeds which may occur in Belgium. (140…150 Kph).

Data from ON4UN element stress analysis.

Material : F22 ALU with tension strenength : 22 kg/mm²

Element weight : 1.1 kg.

Element windload : 13.0 kg.

Element Sag : 4.6 cm

Wind pressure : 115.9 kg/m²

ON THE AIR.

I putted up the beam on a smal telescopic tower almost immediately after finalising construction. I could easily put it up to about 8 meter, which is nearly a wavelength on 10 meter. The VSWR was as calculated, at least on the scale of my TS-850SAT. I didn't have any other measuring device at that time.

I ran some tests and worked several DX-stations I could hear. The next week I presented te small CW 10 meter beam to Franki as promised. His enthousiasm and comments were very positive and the satisfaction after exercise, building and testing this little project was surely worth the effort.

CONCLUSIONS.

• This project will provide you with a good antenna to work DX on 10 meter on a very limited footprint and even with limited mechanical skills you can build one yourself for an attractive budged.
• The antenna was used a few years ago with high sunspot numbers !
• It is a nice small beam which can be placed on the smallest tower.
• The satisfaction is all yours if you work the ultimate DX with your homebrewed antenna-"construction".
• Shouldn't we think about a stack...