Survivalism & Self Sufficiency Topics > Amateur Radio How-To's

The BIG STICK , Half wave , 2 Meter antenna

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Alan Georges:

--- Quote from: Alan Georges on April 28, 2017, 06:29:08 PM ---Rainy weekend in store... might get this one knocked out in record time.

--- End quote ---
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.

Carl:
  Thanks Alan for the report,The antenna is consistent (in 1" schedule 40 PVC)and 52 " overall length with 17 and 3/8" on the short leg. It is the same ratio I use now for an HF antenna of 51 feet and 17 feet with a 4 to 1 balun as feed point to aide matching.Your choice of lighter/smaller PVC and the need to alter wire lengths illustrates how the PVC pipe actually is part of the radiator and conducts at RF frequencies.

  Good work as many may prefer a thinner lighter antenna. I used a pull up whip for a camper version and only PVC long enough to contain the matcher and support the whip...about 30 inches long...tied to a pack frame,and great results. A good SWR meter of ANALYZER is really needed
when deviating from the original....Great work.

Alan Georges:
Thanks Carl.  Yeah, it's plausible that the numbers for thinner PVC should fall somewhere between those for thick Sched 40 pipe and for no pipe at all.  I'm sure these final dimensions could be iterated down to give a slightly better SWR, but this is backyard engineering and the current result is good.

Other projects await – not all of them radio-related.  For one thing, opening day of hurricane season is this week and I still haven't picked up my license.

Carl:

--- Quote from: Alan Georges on May 30, 2017, 06:46:16 AM ---Thanks Carl.  Yeah, it's plausible that the numbers for thinner PVC should fall somewhere between those for thick Sched 40 pipe and for no pipe at all.  I'm sure these final dimensions could be iterated down to give a slightly better SWR, but this is backyard engineering and the current result is good.

Other projects await – not all of them radio-related.  For one thing, opening day of hurricane season is this week and I still haven't picked up my license.

--- End quote ---

It's been so long ago that I forget how to dress out one of them Hurricanes.

Alan Georges:

--- Quote from: Carl on May 30, 2017, 11:14:16 AM ---It's been so long ago that I forget how to dress out one of them Hurricanes.

--- End quote ---
;D

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