W3FF Buddistick(tm) and tripod with Foil Strip Ground
They say that imitation is most sincere form of flattery.
I have been successfully using the Alpha Delta Outpost(tm) tripod system with my W3FF Buddstick (tm) over this past year with very good success. It is great for excursions to parks etc where you can park close to the operating location, but not practical if you need to lug it very far as it is about 3 feet long when collapsed and weights about 15 pounds. (See http://www.alphadeltacom.com/pg6.htm for more details on the Outpost).
Efficiency seems to be excellent so I consulted the ARRL antenna book to try to understand how this works so that I could perhaps build my own more portable version.
Very briefly ... any short vertical located close to the ground is capacitively coupled to both the earth and the antenna's own ground system. The problem is that the earth makes a very big capacitive plate and as a result most of the resulting return current flows through the earth which tends to be a rather poor conductor, and this results in losses and reduced efficiency. What the Outpost(tm) does is to improve the coupling between the vertical antenna and the antenna's ground (itself) by providing a rather large capacitive plate for the antenna to couple to. Most importantly it provides a fairly large surface area near the base of the antenna where the currents are more concentrated. The whole idea is to get a large portion of the return current flowing through the Outpost(tm) Base rather than the lossy ground.
So in a nutshell the Outpost is literally just a big capacitor plate. The same effect can be had with radials laid on the surface of the ground, but you would need a large number of wires evenly spaced to get a similar effect.
Ok enough theory. So what did I do. Well, I went to Home Depot and bought a roll of Aluminum foil tape (in the heating/ventitlation section) and a roll of heavy plastic. Note that the foil tape is sticky on one side. I rolled out the plastic and put three strips of the tape, each 9 feet long (this approximates the surface area in contact with the ground on the Outpost(tm)). I then took a pair of scissors and cut the resulting strips out of the plastic sheet leaving a bit of extra plastic on the sides.
A couple of important points. At the ends of the strips where I connect them together at the Buddistick tripod, I actually looped the foil tape around the plastic to the underside, and punched a hole with a single hole punch so that I could stack the ends over the screw holding the antenna mount to the tripod and get a good electrical connection between strips.
During the initial trial of this system I found that I needed to secure the strips to the ground to keep the impedance constant when it was windy. My solution was every foot or two to reinforce the strip with a piece of duct tape and push a 2.5" galvanized nail through it to hold the strip firmly to the ground. Also note that I use the strips with the plastic sheet side down to hopefully prolong their useful life. As a further enhancement I also use an elastic to hold the strip in place against Buddistick tripod leg on its way down to the ground as I found that if this part blows around it also impacts the antenna impedance.
One last point .. as you are no doubt aware capacitance increases as the distance between the plates decreases ... so there is an advantage to elevating the base of the vertical antenna even a couple of feet off the ground as that will reduce the coupling between the antenna and the earth even further. I use my Buddistick tripod fully extended and secure it to the ground with a small tent peg and a bungie cord.
I haven't had a chance yet to do an A/B comparision with the Outpost but I can say that this system works and works well and I have no issues with getting better than 2:1 SWR on all bands from 10m through 40M. Each of the strips rolls up into a small cylinder about the size of a film cannister so it is very compact.