A 2 Meter J-Pole Jig
Last week’s McARCs meeting/workshop in Mendocino was a lot of fun. The turn-out was good too — better than anticipated. I’d like to thank all of those who made this meeting possible and who helped out with the antenna workshop.
One of the interesting demonstrations was Alan’s (WA6JBK) j-pole jig which he uses to rapidly construct 2 meter J-poles from ordinary copper pipe (same as used for home plumbing). Notice how Alan decouples the coax by passing it within the lower segment of the antenna pipe.
I use a similar J-pole made by Len, WA6KLK, and they’re strong, easy to setup antennas that work quite well. Here’s how to make a J-pole — but note the difference in how the coax is attached. (It would be fun to electrically compare the difference in the two decoupling methods: wire loop vs. Alan’s copper sleeve.)
Another antenna construction project presented by Steve, KJ6EIF was a hands-on build your own super cheap 2M Yagi-Uda antenna (for only $5). The design is based on WA5VJB’s cheap yagi. Steve made one about a year ago and it tested out pretty well.
We made the Yagi antennas from lengths of ordinary #12 house wiring attached to wooden garden stakes. The feed method was a simple half-folded dipole (no gamma match or balun needed.) All-in-all it took about an hour to build each antenna.
Unfortunately… after construction, we discovered that our antenna resonance rang up around 143-144 MHz, quite a lot lower than we had intended. We experimented around a bit with shortening the driven element and shunting its folded-side, but neither changed the frequency by much (although the shunt did give better control over SWR.) We suspect the culprit to be the insulation we left on the directors. We kept it on to make the elements stronger in the wind, but insulation will affect the velocity factor, making those elements electrically longer than they should be. On a Yagi-Uda, you can get by with directors that are a bit too short, but if you make them too long, the phasing of the array is quickly spoiled. Well, not a problem… we will try snipping down the directors to see if we can get the Yagi where we want it. (We’ll let you know how this works out.)
Thanks again to all of those who made this workshop a fun and educational McARCs meeting.