build the pac-12 antenna
a multi-band portable vertical designed by ka5dvs
here’s an award-winning, easy-to-homebrew, multi-band portable vertical antenna designed by long-time antenna aficionado james bennett, ka5dvs. he’s documented the design and construction plans for a portable antenna that can be built with relatively ordinary components obtained from the local hardware store, including replaceable loading coils. this is a very cool antenna that's efficient and can easily be taken it along on quick trips to the field. you’ll love it!
note: this article was originally published in issue #8 of qrp homebrewer magazine, and is posted here with the permission of author ka5dvs and the njqrp club. watch for pac-12 mods and other antenna designs coming from ka5dvs, as being chronicled in the pages of qrp homebrewer.
introduction
as someone who travels quite a bit on business, i am always looking for ways to take along my ham radio hobby. with the availability of a new class of small qrp rigs such as the elecraft k1 and k2, sgc 2020 and the yaesu ft-817, it has never been easier to take our hobby on the road ( or bus or train or boat or plane).
when i first started traveling with radio equipment, i typically used a random wire and tuner to keep the total antenna package small. however, with the wire, launching weights and string as well as a tuner and swr bridge, the entire package gets somewhat bulky. not to mention the batteries, cables, key, microphone and other radio accessories. keeping the total weight of luggage to a manageable level is a primary goal of mine. i have tried a few designs based around the 72" telescoping whip from radio shack coupled with an l- network tuner. while these designs proved usable, i was not happy with the configuration and portability of the design so i continued to think about a way to make a better travel antenna.
commercial antennas have come on the scene, these include designs such as the outbacker, superantennas mp1 and mp2, maldol whips and a wide range of mobile antennas that can be adapted to portable operation. however, none of these quite fit my needs for a lightweight, packable antenna. thus, i decided to try to build my ideal travel antenna.
building antennas is one of my favorite activities in amateur radio. i often find myself browsing for antenna materials in the local home depot or other hardware store. over the years, like many of you, i have built many dipoles, verticals and a few beams from a wide assortment of wire, tubing nuts and bolts. on one such trip, i ran across some 1/4’ aluminum rod and threaded couplings and started to think how i might use these items in an antenna. that day, a pack of couplings and a couple of sections of the rod followed me home. using a threading die, threads can be cut into the ends of the rod to allow it to screw into the couplings. soon, i had several sections threaded. i ended up making each section 12" long as that seemed a convenient length for antenna sections. i already had several of the radio shack 72" telescoping antennas that collapse down to almost 12" as well as a good selection of pvc fittings and pipe used in previous antenna projects. after a bit work, i had an antenna that would break down into 12" or less sections and when assembled would be approximately 8’ in length. i chose to move the loading coil away from the base to improve the efficiency. two 12" sections of the threaded aluminum rod were used to make the base section. for the coil, i used 2 pvc caps and a section of tubing along with 2 bolts, washers and nuts to produce a coil assembly. wire from one of my other favorite haunts (radio shack) was used to wind the loading coil on the pvc coil form. a pvc fitting, a bnc connector and a couple more bolts, nuts and washers and the antenna was complete. i eventually named it the pac-12 where pac stands for portable antenna concept and the 12 comes from the length when disassembled. it is also a bit of word play on the pac-10 conference.
the antenna has served well on many trips and has continued to evolve, making it easier to construct and assemble for use. on a whim, i entered it in the hfpack antenna shootout held at the pacificon conference in october 2001. i was somewhat surprised to have the antenna place first in efficiency as compared to a 1/4 wavelength wire vertical.
also see appendix c at the bottom of this page for many examples of pac-12 antennas as constructed by qrpers in the njqrp club.
i hope many of you will build and use this antenna, please drop me an email and let me know how it works for you.
james bennett, ka5dvs/6
1196 phillips court
santa clara, ca 95051
email:
ka5dvs@arrl.net .
