Optimal Buddipole Antenna
This is the Buddipole vertical antenna made specifically for 20 meters. The antenna consists of the following parts (Buddipole part numbers shown in parenthesis).
1) Buddipole tripod mount (BPT),
2) Buddipole 16 foot mast (BML),
3) VersaTee interface to antenna element where guys attach (VTE),
4) 3 sections of 22" mast (XAA) plus the long telescopic whips (black) vertical fully extended (LTW),
5) 2 counterpoise guy wires (The Wireman, #545) cut to 16.5 feet and a third guy made from Dacron rope (The Wireman, #816).
The counterpoise wires are the 2 wires joined together at the midpoint of the antenna structure, joined onto the VersaTee black terminals. The two counterpoise elements are made from copper FLEXWEAVE #12 AWG with Black PVC jacket. The wire tensile strength is 196 lbs. The tensile strength for this Dacron rope is stated as 770 lbs so it should hold up the antenna in higher winds. The Dacron FLEXWEAVE (No. 545) and Dacron rope No. 816 can be purchased from The Wireman.
Note that the wire rope is fed through the end insulator, knotted, heat shrink tubing applied and then terminated in a 3/8" diameter ring lug.
This method removes all stress from the ring lug and keeps it on the wire rope where it belongs.
VersaTee with Top Insulator and Wire Rope. Bolts on each end are 3/8" dia. x 1/2" long plus lock washer, stainless steel
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One interesting variant is to use an alternate feed line and connect the black and red terminals so the counterpoise actually becomes an inverted-vee antenna. By switching feed lines between the vertical element (blue terminal on VersaTee) and the red terminals, an effective Vertically / Horizontally polarized antenna can be created. This should allow for optimization between DX / NVIS operations, respectively.
Double feed lines can be brought down the mast or a small relay can be used to select between the two antenna - your choice. A bias-T can used in the shack and at the antenna to inject and extract the 12 VDC power to provide relay operation.
A feed line length of an electrical quarter wave can also be chosen and the coax end left unterminated (which is an open circuit). The open circuit translates to an electrical short at the red and black terminals. If this technique is selected, the relay must disconnect both center conductor and shield of the inverted-vee feed line. I hope to gather some S-meter data between these two configurations to demonstrate if this is an effective choice for the ham radio operator. Figure 3 shows the antenna erected at our Field Day site.
Another configuration is to used 4 guy wires to support the mast, two that are the counterpoise for 20 meters and another two that are cut to 40 meters (about 66 feet for each leg). Each leg of the 40 meter guy wire should be connected to a leg of the 20 meter guy wire. The 20/40 meter dipoles are essentially in parallel and operate independently since the bands are a factor of 2. This means at 40 meter, the 20 meter antenna has minimal affect to 40 meter operation. At 20 meter, the 40 meter dipole appears as a very high impedance and also provides minimal affect to 20 meter operation.
The tri-band feature uses the 40 meter dipole at its 3rd harmonic to achieve operation on 15 meters. Thus the overall antenna will provide 40/15 meters and 20 meters on one mast. Pretty neat idea for portable operations.
Since no switching is needed between the 40 and 20 meter dipole guy wires, the 20 meter vertical section can still be employed when the tri-band operation is wanted. This will allow optimal polarization selection for the 20 meter band.
Above is the alternate configuration for a dual feedline approach (Click to Download a PDF file)
Completed Optimal Buddipole Used During Field Day
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Antenna tuning is accomplished by folding back the counterpoise end points so the overall length is varied. Folding back the elements allows for the overall length to be adjusted shorter or longer as needed during the tuning process.
The ends of the wires feed through an antenna insulator appearing white in the photo above. Once folded back, UV resistant tie-wraps are used to secure the wire to itself keeping the chosen length constant. By symmetrically adjusting both counterpoise elements at the same time and then taking a VSWR measurement, the antenna resonance can be optimized for the 20 meter band. I had no problem getting the antenna to resonant over the entire band that was an easy impedance match for my transceiver.
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One thing about wire antennas is the fact that they can be easy to store. The Optimal Buddipole can be rolled up onto a cable spool that is found at your local Lowe's or Home Depot. It is commonly used to roll up power extension cords. Just roll it up and put it away until it is needed on another day.
Roll-Up Antenna Spool
Download these Documents
Download the Optimal Buddipole document now: The Optimal Buddipole (PDF)
Download the Optimal Buddipole Alternate Configuration Drawing now: The Optimal Buddipole Alternate Configuration (PDF)
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