Wednesday, July 05, 2006

Antennas for travel: Buddipole

This is a long post. Sorry. But, this post talks about the one antenna system I rely on most for my trips. I hope you enjoy it.
One of the simplest and most effective lightweight antennas is the trusty dipole antenna. When we say "dipole" we're really talking about a whole family of antennas with various shapes and sizes but they all have the same constituent parts: two arms, a feed point, and possibly a matching network or transformer to present a convenient impedance to the transceiver. Dipoles have a major advantage over a quarter wave vertical antenna: there is no need for an elaborate radial system to make it work efficiently. The two arms do the trick nicely.
A typical half-wave dipole is fed in the middle with arms of equal lengths on either side but there is nothing magic about the middle of the dipole. It is just as valid to feed the thing off center (making an off center fed dipole). As you move off center, the impedance of the antenna goes up compared to the center fed cousin but a matching network can take care of that. We can even use the fact that moving off center raises the impedance to our advantage as we'll see later.
Some of these specific designs have become popular enough to have been named such as the Carolina Windom and G5RV. These are wire antennas that weigh only a couple of pounds and operate well on many bands. For example, the G5RV covers 80-10m, every HF contesting band except 160m! So, if these antennas are super lightweight, cover multiple bands, and are well-proven by years of use, why don't we just carry one of these on our DXpeditions and declare victory?
The answer is simple: these antennas work well when hung high in the air and many places we might visit on a DXpedition will not have any trees, or indeed any structures, that are tall enough to hang the antenna high enough to make them effective. Further, if you want to have a wire antenna in a flat top configuration you'll need to hold it up in three places: the middle and the two ends. If you live in an area like New England with its nice tall pine and oak trees then getting a dipole pulled up high is pretty easy. If you are looking for a tall tree on a tropical island where hurricanes periodically flatten everything, the task is a lot harder.
The Buddipole provides nice solutions to many of these problems. In its simplest form, the Buddipole is a dipole antenna made from stiff aluminum parts and whips. To add electrical length without adding too much physical length, two coils (one for each arm) are supplied. The coils may be tapped anywhere along their lengths as needed to give you a good match. An antenna for the VHF bands (2 and 6m) can be made with just whips and arms alone. HF antennas require the arms, whips, and coils.
Like the Buddistick and Super Antennas MP-1, the Buddipole is made using parts with 3/8-inch x 24 threads. The standard configuration is center "tee", then on each side one 22-inch aluminum arm, a coil (usually tapped except on the bottom band 40m), followed by a whip.
You can see how well the Buddipole performed in the HFpack Horizontal Antenna Shootout. Budd Drummond tested three configurations: the standard configuration described above, a configuration with an extra "aluminum arm" on each side (adding 22-inches of arm), and finally a configuration with two extra arms (for a total of 3 arms). When compared to a reference antenna (a 20m wire dipole) the short version was just one dB lower in power than the reference antenna, the two-armed version was neck-and-neck with the wire antenna, and the 3 armed version outperformed the reference dipole by a hair. Clearly, this is a no compromise antenna for 20m and up!

The shootout compared the performance of the Buddipole to a standard 20m dipole with each hung horizontally. The Buddipole need not be a horizontal antenna, however. A "rotating arm kit" allows you to adjust the position of each side of the Buddipole. You can make a vertical dipole by rotating the arms so the "hot" side is up and the "shield" side is down. You can also make an "L" shaped antenna with the "hot" side up like a vertical and the "shield" side like a single raised radial. I've talked to Europe from a park near my home with just 8 watts SSB with the Buddipole in this "L" configuration.
The ability to add, subtract, or substitute parts in this antenna system is something that drew me to it. I believe the Buddipole is the Erector Set of ham radio. You are limited only by your imagination! I have found this system to be so versatile that I have purchased two whole systems:

  • Big Buddipole system -- This system consists of the Buddipole antenna, matching tripod, 16-foot mast, guying kit, two extra aluminum arms (four total), 5-section shock-cord whips (longer and stronger than the stock whips), the rotating arm kit, and a Triple Ratio Switch Balun (TRSB) which gives me 1:1, 2:1, or 4:1 matching with a quick turn of the switch. It all fits into a nice bag (and weighs 12 pounds). You can see pictures of this from my St. John trip here.

  • Little Buddipole system -- This was the original system I bought which consists of the Buddipole antenna, matching tripod, 8-foot mast, the rotating arm kit, and the TSRB. At 8 pounds, this is the one I grab when I want to do some quick picnic table portable some place. (Remember, even this configuration was nearly as good as a full-sized dipole on 20m!)

This antenna system covers many contingencies that would be difficult to cover otherwise. It gets your antenna off the ground. It provides a great antenna for 20-2m and a pretty good radiator for its size for 30 and 40m. You can even leave the tripod and mast at home and attach the antenna to a painter's pole. If you knew you could obtain such a pole locally once you arrived at your destination, this would be a great alternative to carrying the tripod and mast. This isn't cheating! Using local materials, especially if they are heavy, is a perfectly reasonable thing to do--if you know you can do it.
There is a Yahoo! group that supports the Buddipole and its companion Buddistick. You can find that group here. The product is well supported by Budd and his son Chris. The nice thing about the Yahoo! group is you can join before you purchase the antenna and any question you pose will be seen by the thousands (!) of users within the group. It is unlikely any question would go unanswered for long.
I try to bring one or both (Big and Little) Buddipole systems on each big trip because I know I can make it work, even if nothing else will. That's a nice feeling to have far away from home.
Tomorrow I'll either talk more about the Buddipole or, perhaps, I'll move on and tell you why I ordered the Force-12 Sigma-5 antenna. Until then, 73!


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