2020-01-26 It's been several years since I even thought about this antenna other then it's been in a plastic bag under my bench, often in the way! But preparing for Winter field Day yesterday I got to thinking about it. Actually it had come to mind after a QSO with KW4JM who was doing a SOTA activation on a mountain in Western North Carolina last week. I was QRP using my 29ft EF wire and he had to struggle to copy me so I emailed him afterward and told him I appreciated his sticking with me. That resulted in the exchange of a couple emails. I asked him about his antenna, rig, etc. and he sent me a link to a YouTube video describing his No-Stick Buddy-Stick Antenna he made. That inspired me to get out this Pac 12 and think about using the coil to duplicate his work.
Then today I thought I'd just put this thing together and see what it looked like on my NanoVNA which I have set to show the SWR curve all the way from 6mhz to 30mhz. So after a few minutes I had it together, found an old 12 ft piece of speaker wire to use as a counterpoise, leaned the thing up against the couch and took a look. I had multiple taps on the coil and found the one for 40 meters. Withe just a little tweaking of the collapsible whip it had a great SWR on 40. Same on the 30, 20 and 15 meter taps!
That inspired me so I quick got my xiegu x5105 and hooked it up. Nothing heard on 40. Nothing heard on 20. But tuning across 30 meters I heard N5XE in QSO with another station which I couldn't hear. But Carl was S8! Wow. After he signed he called CQ and I replied. That resulted in a nine minute solid copy QSO. He gave me a 559 and he was a steady 589. He was running 50 watts to an inverted vee 35 feet up. It takes quite a bit to get me really excited. But that did it! Thanks Carl for a highlight in my ham radio life! After shivering my butt off in the unheated, detached garage yesterday for Winter field Day, what fun to have "arm chair" copy, in the living room with the antenna sitting on the floor leaned up against the couch and the radio on the coffee table! That's Ham Radio for you! The Pac 12 is back in my good graces again!
What is a pac 12 antenna? Simply put my version is a center loaded vertical. Click this link to see a PDF about it. The above photos show mine. It's assembled full length is 9 feet. It is made of a collapsible whip, three 12 inch 1/4 inch aluminum rods threaded on both ends and one additional 12 inch rod which is threaded on one end and sharpened on the other to be used as a ground stake to old it up. I made a PVC pipe thing with a SO239 coax jack on the side as shown. The SO239 Center pin goes to a 1/4 inch brass bolt on the top end and the SO239 ground side goes to a 1/4 inch brass bolt on the bottom end. The sections are all held together with 1/4 inch steel couplings.
The loading coil is wound on a PVC pipe with 1/4 inch brass bolts in each end. The top end of the coil is connected to the top bolt. The bottom end is open, not connected to anything. The pigtail with alligator clip is connected to the lower brass bolt. It can be connected to any of the taps on the coil. I made the taps by simply forming a twisted loop at the appropriate points along the coil.
The inductance of my entire coil (bottom tap) is 42uh. Next tap up is 35uh, 3rd is 30uh, 4th is 14uh, 5th is 7uh, top tap is 1uh. I share those just as ball park figures. The exact values can be different in your situation. The major factor will be the fully extended length of your antenna. I actually made an additional 117uh coil so I could tune it on 80 meters. I can't recall whether it is used in addition to or in place of the mail coil.
My main point is simply to inspire whoever reads this. I find great fun and fulfillment out of playing with antennas and want to share the fun.
Several years ago I ran across the PAC-12 vertical and had some success with my home built version. If nothing else it is an interesting project to build and you get quite a thrill when you make a contact with it.