The well known Hustler "xBTV" (x Band Trap Vertical) series of antennas provide simplicity with proven performance and ease of assembly. They are frequently available used for under $100 but even a brand new 5BTV 5-band model will set you back less then $200. Replacement parts and aftermarket gadgets are available from a number of retailers.
I was able to horse trade for a 5BTV that just needed a new base assembly, and after a quick order on the DX Engineering website (www.dxengineering.com), my new vertical was ready to go. I cut four ground radials for 20m in accordance with the assembly instructions, soldering a lug to one end and covering the other end with a wire nut and electrical tape. I buried these radials just under the surface of the grass and they have appeared to work well. Since that time, I have read numerous papers on ground radial systems for verticals (I've provided some links below) and have now learned that when the antenna is ground mounted, radials need not be "cut" for resonance. They should all be about as long as the antenna is high with the key that more is better, any length. (This does not apply to above ground (i.e. roof) mounting, those need to be cut to freq)
Being a trap antenna, I was limited to the original five bands (80/40/20/15/10 meter), especially since the manufacturer was pretty adament about not using an antenna tuner (its supposed to be tuned for all bands when first assembled) so I began searching for ways to add additional bands, specifically 17m, 12m and if possible, 30m (I'm a big digital operator). It didn't take me long to find others who had been on the same quest and a few that solved it.
EASIEST: Buy a ready made trap or add-on
Several companies sell add-on kits or traps for bands like 60, 30, and 17 meters. PRO: Simple, quick, no fuss. Bolt on, tune up, operate. CON: Cost. A 17m add-on will cost you $50, and 60m for $70. A kit to add 30M to the 4BTV amd 5BTV can be purchased from several online retailers for about $50.
MODIFY: If you have access to some basic metal working tools, you can fabricate a rectangular bracket that will mount between the top of the base assembly and the lowest tube. A center hole is drilled just large enough to slide over the tubing. The length should be long enough to allow 12" either side of the tube center (Option: Cut individual bars, about 15", bending one end at a 90 deg angle and using hose clamps to secure it to the main radiator. The upside to this method is 3 can be used, at 120deg offsets, for mounting 3 new bands)). 3/8" Holes are drilled approximately 3/4" from the edge, centered, to allow mounting of standard "Ham-Stick" style mobile whips. (a few "modders" have bent the last two inches of the support at a 45 deg angle from horizontal. There is no data to support either method over the other) Mount a 17m whip on one end and a 12m on the other! (and a 30m whip, if you use the individual bar method) Each will run you about $25. PRO: Much less expensive, satisfaction of home brewing, no permanent modification to the antenna. CON: Requires some metal work
CHEAPEST: A few feet of wire, some wood or plastic dowel, a couple wire ties, a couple of hose clamps. Using the tried and tested formula, Length(inFeet)=234/Freq(inMHz), measure and cut a 1/4 wave length wire, plus a few inches for trimming. For 17m it would be about 13 feet (234/18.130MHz = 12.91 feet). For 12m, 9.5 feet (234/24.940=9.38) (A quarter wave for 30m will be 26 feet long, a bit too long for this application). Drill holes in the ends of the rods, large enough to pass the wire through. Mount one rod near the bottom of the antenna using the hose clamps (or wire ties), another about 9 foot up, and another just over the 20m trap, approximately 13 feet up. Solder a spade lug to one end of each wire and attach the wires to the central coax tie point at the very bottom of the antenna. Thread the wires through the holes in the rods. Adjust the rod at 9 foot point up or down until the 12m wire just barely pokes throught the top. Temporarily secure the wire with either a wire tie or clip. Thread the 17m wire through the first, second, and third rods, temporarily securing it (adjust the top rod as necessary). Using an antenna analyzer, double check the resonance of each band and trim the wires as necessary. Once every thing is tuned up, secure the wires with wire ties and place a dab of all-weather caulk on the exposed tips of the wires. Presto, two bands added!
Alternative method: Requires dis-assembly of the antenna. Using flat 1/4in plexiglass sheet, cut four strips 2" wide by 14" long. Drill a 1.25" hole in the center, and one 1/8" hole at each end, on center, 1" from end. Starting at the lowest tube (just above the base assembly), slide one bar onto the tube and replace. Just above the next trap, repeat the process. The last bar should mount just under the 40m cap-hat. Attach wires as described above, thread through plexiglass. Adjust the bars up or down to evenly support the wires.
For details of mods completed on my 5BTV, click here
SUMMARY This is an established antenna with a long history. For about $40, an additional 30m trap and the 17m and 12m wires will give you an 8BTV (A 9BTV, actually, since this antenna will tune up on 6m too — the 12m wire is an almost perfect 1/2 wave for 50.125 MHz!). Below are some links to a number of the referenced write-ups on these mods, including pictures. One includes a really neat way to add a SO-239 connector to the base of the antenna, as opposed to the pigtail design. DX Engineering has recently started selling these, ready to bolt on, for less than $20. NOTE: These mods are not of my design and credit should be given to the original experimenters.