INTRODUCTION TO POWABEAM ANTENNAS - PLEASE READ BELOW!
Most of the 'Direct Feed' yagi designs detailed in the pages of this website were originally intended as State-of-the-Art commercial designs for PowAbeam Antennas. They are as a result of a more than six year long research project started in late 1994 and ending in 2001. Countless thousands of hours were spent in the optimisation process and subsequent rigorous testing.
Inspiration came from the legendary work of Guenter Hoch DL6WU and Rainer DJ9BV. Thanks to top DX'ers Joe Ludlow GW3ZTH and the late Norman Vincent G3NVO who provided invaluable support testing my designs in both fixed station and portable applications.
The design concept is focused on the 'Current Distribution Profile' ensuring that ALL of the yagis elements are active. Thus the 'Optimised Current Vector Yagi' was born, a phrase quoted in the original advertising literature describing the unique nature of these antennas.
The designs are published here to encourage fellow Radio Hams to experiment and 'have a go' at building their own antennas!
Shalom Cohen 4X1UN (KM72JB) constructed my three element 2M 'Direct Feed' yagi and had a record breaking E's contact on June 6th 2007 at 16:24 UTC working CT1HZE (IM57NH). A staggering distance (QRB) of 4008.06KM (2,490.49 miles), a feat normally only attributed to the Big Guns! Well done to Shalom!
E-mail received from Richard Mason G6HKS
Derek, Also just for your info I worked RA6AX on Monday night on EME with 40 watts into the 9 ele CQM, he was -6 (S1 on the meter) which is strong and got -24 by return (full power we may have been able to make it on SSB)? Good condx but this really vindicates your excellent design and the direct drive element is great. Like you I cant believe people still go for baluns etc to match their elements and take the .2db loss !!!
73's Richard G6HKS
FEEDER CABLES
Ignore this at your peril! Use the best quality cable and connectors you can afford. Keep your feeder cable run as short and direct as possible. Finally, minimise the number of external connections, making sure they are completely weather-proof! I have just upgraded to ECO15 flexible low-loss coaxial cable available from Diode Communications.
Element Rod, Tubing Sizes and UK Suppliers
In the UK we are still using imperial sizes. All of my designs except the 4X1UN three element are constructed with tubing purchased locally from Blackburns formerly Baco Metal Centres (CLICK).
Alternative suppliers here in the UK are Forward Metals Ltd (CLICK), Smiths Metal Centres (CLICK) and finally, George King Metals - 224 Tooting High Street, Tooting
London, SW17 0SG - Tele: 020 8672 8538.
My 50MHz designs use 5/8 Inch OD tubing (15.88mm) for the Driven and Parasitic Elements, you will need to fabricate insulated above the boom supports.
BOOMS
144MHz yagis that are longer than my 2.5 Wavelength design will require an overhead support wire.
This also applies to the 6M 1 wavelength antenna.
Suitable round section alloy 6082T6 seamless drawn tube (used in hang gliders and microlights) can be obtained in sizes of 1" (17swg), 1 1/8" (17swg)
and 1 1/4" (17swg). With a wall thickness of 1.42mm this tubing makes up a
TAPERED BOOM with very good slide in fit properties and low wind
profile. Please note however, that if you purchase a PowAbeam Antennas yagi kit the boom is of square section.
USING NETLON CLIPS
On square section booms two self tappers provide a simple and efficient way of securing the clips. However, on round booms the 'Netlon' clips will
require their spine to be enlarged by drilling out to M4 size.
Then secure with stainless steel studding cut to length and a stainless steel size 8 self taper
located in the remaining hole (under the element) to stop rotation.
Use stainless steel shakeproof washers and nuts to hold the studding.
In ALL cases regard the spine of the clip as the rear. Note that the element is then offset forward by 8mm. You will need to allow for this in determining the absolute positions of ALL the yagis elements.
DRIVEN ELEMENT MOULDING ASSEMBLY
Last but not least is the Driven Element, it is in fact a 'Coaxial Dipole' and has been specifically designed for use in a 50-Ohms natural impedance yagi beam antenna. It is unrivalled in its simplicity and when used in a 50-Ohms direct feed yagi it will produce a highly efficient and low noise solution, ideal for weak signal communication!!
It will withstand huge power, your feeder will probably burn out first! At its centre is the moulding which locates the tubing precisely and keeps the weather out with 'O' ring seals as seen above.
1. deassembly.doc
2. demoulding.jpg
3. tail.jpg
Please note that the 'Netlon' clips used from 144MHz upwards hold 3/16 Inch OD rod (4.76mm) but will take 5mm sold in Europe. However, the Driven Element Moulding was designed specifically for 5/8 Inch OD tubing (15.88mm) and it is not advisable to use 15 or 16mm OD supplied in the EU.
