Rainy weekend in store... might get this one knocked out in record time.
Finally finished it today, a month after my optimistic estimate. So much for "record time."
Minor modifications... instead of 1" Sched 40, I went with 3/4" SDR 21. It has a thinner wall, and 450 ohm window line just fits inside. Makes for a lighter antenna that's less suited for base applications, more suited to hiking, etc. Not "better," just "different application."
Naturally this difference in PVC wall thickness changed up all of the dimensions. Freely adapting Carl's numbers and cross-checking with several online j-pole dimension calculators, after tuning the final numbers are:
450 ohm line length: 17.3"
feed line tap (from end of 450 ohm line): 2.2"
total length: 54.3" (+1" extra to turn over at the end)
There's maybe 4' of extra PVC below the window line section. I cut off about 2' from the original 10' length to make it a less unwieldy, less floppy. The length's not critical, but whatever you're planning on attaching it to, leave enough PVC below the ladder line section so things don't interfere. Especially if you're attaching it to any kind of metal pole, frame, etc.
Used 12 gauge wire because it's what I had on hand. It's definitely overkill. Instead of Carl's crimped-on lug at the end, I turned over 1" of the end and zip-tied it down with a piece of bank line in the crook; the bank line slips under the PVC cap and holds things up. If you have an antenna analyzer, cut it about 3" long and trim back to tune; otherwise, just go with the numbers above. Didn't cinch down the zip-tie until everything was tuned up. The coax just hangs out the bottom, then it's looped back up and zip-tied on the outside to give strain relief.
SWR is < 2:1 from 144 to 151 MHz, bottoming out at 1.2 around 147-148 MHz. Frankly, I cut it about 1" too short, but this is good enough. What can I say, storm was closing in and I was in a hurry.
Carl, much thanks for the inspiration and for the original design.
