[TowerTalk] Magic Length for 160-40 vertical?

[Kirk Kleinschmidt]

Hi, gang,
I'm in a bit of a race against the clock (the winter clock), and I'm trying to get a vertical up in the back yard that might be useful on 160-40. (Never used a vertical before, but I wanna.)

Assume that I have plenty of 50-foot radials or a 500-square-foot galvanized ground screen (Rochester reportedly has excellent ground conductivity).

My other antenna (until Spring, when towers can go up) is a 102-foot doublet fed with open-wire line, up about 40 feet (not exactly killer on the low bands for DXing). The vertical doesn't have to be "the final design," as it can be changed in the Spring, but it does have to be quick, as my pre-winter window is closing soon. 

I am thinking about feeding it with an SGC or Icom autocoupler for ease of multibanding, but I would consider making dedicated feeds for various bands (100 W max for this first winter season).

The main vertical element will be a 30-foot length of aluminum irrigation pipe, either 3 inches or 6 inches in diameter. I'm not sure yet, as I don't know which will be available to me. The 6-incher is 70 miles away, the 3-incher is 120 miles, and I have to transport these pipes with a Ford Focus and an 8-foot utility trailer (and lots of back roads).

30 feet is close to a quarter-wave on 40, of course, and I can add a top-mounted loading coil. a top-mounted trap, a capacitance hat near 30 feet (like a 20 meter quad loop mounted parallel to the ground), or a 22-foot fiberglass "whip" with heavy-gauge aluminum wire inside (or a combination).
Without presenting "too-crazy" impedances on one band or another, is there a "magic formula" for something like this, or is the frequency span just too great?
As always, thanks,
--Kirk, NT0Z  Rochester, MN

My book, "Stealth Amateur Radio," is now available from www.stealthamateur.com and on the Amazon Kindle (soon)