The 2m J-Pole Field Antenna

In yet another effort to get on the air while being able to respond the XYL's never-ending request to "Take that f@#%&ing antenna down!", I've finally put together a reasonable solution for 2m... the 300 ohm twin-lead J-pole deployable as a field antenna (or a temporary antenna here at home. There are multiple sites that describe this version of the twinlead J-pole -- here's one example. Another site shows a design of a self supporting J-Pole. I tweaked the design of the PVC housing a bit, and this is what I came up with...we'll start with a few pictures...

Taking a closer look, the following photo has been annotated to show the details of the business end of the housing. The picture pretty much tells the story, but a few notes are in order. First, the 1/2" CPVC slip-slip couplers taper from the center towards each end. I ground away the taper on one side so it snug-fit into the upper 1/2" PVC coupler. Second, I opted to include three FB-56-43 ferrite beads from Palomar Engineers over the RG8x coax to prevent RF on the shield. In total, these three ferrites are about 3-3/8" long. The short length of 1/2" PVC tubing between the upper and lower PVC couplers was added to just barely provide the necessary space for the ferrite beads. A hole was drilled, at an angle, into the PCV slip-thread coupling to allow the RG8x to escape.

Prior to the tune-up with my trusty MFJ-259B, I used PVC cement to assemble everything except the 1/2" CPVC tubing. This allowed me access to the twinlead to make the neccessary adjustments by just slipping it off. The built-to-spec J- pole resonated at ~141 MHz when in the CPVC tubing so I had to trim a bit off the radiator and the matching stub to bring this up to ~146 MHz. The final SWR readings are < 1.5:1 accross the whole 2m band. :-)

With the tune-up complete, I trimmed the 1/2" CVPC tubing to just accomodate the final length of twinlead, cemented it into the uppermost CPVC coupler, and topped it off with a CPVC cap. Finally, I added caulking to the point at which the coax leaves the housing.

The Acme thread on a painter's pole roughly fits (in a cross thread-ish fashion) into the threaded end of the 1/2" PVC slip-thread coupler, but I decided to order the Center Tee to Painter's Pole Adapter from Buddipole -- I order two actually since I'm also starting to experiment with the homebrew Buddipole design.

I use the same trick for getting the coax feedline back to that shack that I used for my 450 ohm ladder line...run it from the shack to a corner of the deck and make it easy to connect and disconnect! I used 35' of BuryFlex coax from Davis RF from the shack to the corner of the deck (leaving 115' to eventually bury accross the back yard when my XYL lightens up). I devised a housing for the SO- 239 connector using PVC fittings and used epoxy paste and electrical tape to seal it up in an effort to keep the water out. This makes it a little tough to tighten the PL-259 (it requires the use of long nose pliers) so, as a workaround, I added a short length of garden hose to the PL-259, using caulking to glue it to the outer barrel. This serves two purposes: A no-tools assembly (no tools to loose!) and additional shielding from the elements.

With this antenna, I'm able to sit in my shack and reach the Paxton 146.970 repeater with 2 watts, full quieting...and with this incarnation, I don't have to worry about the weather getting in and wrecking things (I hope...)!.

UPDATE: A couple points on the antenna as described above. First, the caulking didn't hold up very well and doesn't have good adhesion on the PVC. I used coax-seal (that stickey rubbery stuff) and then wrapped the whole thing in white electrical tape to hold it in place. Second, the short length of garden hose is tough to get a grip on if it's wet...I've wrapped an elastic band around it to, hopefully, provide some grip the next time I try to take it down in the rain.

I've also taken a close-up of the bottom ferrite as is visible when the "Center Tee to Painter's Pole Adapter" adapter is removed. There is absolutely no "wiggle room" in there so the beads don't rattle around at all.