The 2 Meter "J-Stick"
By Mark Griffin, N5HII
 

Being a relatively new ham, my first thoughts were like everyone else, to get on the air as quickly as possible. It didn't take me long to become frustrated with the performance of the 1/4 wave mag mount that I bought as a cheap and fast way of getting out and talking. I thought maybe a 'Hamstick' or something like it would do a better job for my mobile, but I really wasn't sure what would be best. I also wanted an antenna for the house, as sitting inside is infinitely more comfortable than huddling in the truck if it's cold or rainy. After talking to other hams and searching the net, it seemed like the next best step for a home rig would be a j-pole, either copper or twin lead. Well, to make a long story short, I combined the two ideas, and the "J-Stick" was born.

First of all, I rummaged through my shed and located an old Firestik 7' CB antenna that was long lying dormant. I pulled off and saved the rubber end cap, and then stripped the plastic covering off, and then spooled off all of the copper windings, leaving a 3/8" fiberglass whip with a 3/8-24 threaded mounting stud.Next, I made a standard j-pole antenna out of 300-ohm twin lead. I'm not going to recount how to do that, as there are dozens of examples on the Web. It's important to get it tuned for a low SWR, as you'll be modifying it and need a good known starting point. Check it at 144, 146 and 148 MHz. Once the antenna and its coax feed line were completed and tuned, I started
bringing it together. Starting at the top of the whip, I taped on the j-pole using electrical tape in 4 or 5 spots. Be sure to tape the feed point securely. >Now is a good time to re-verify that your SWR is where you want it to be. Remember, a j-pole wants to be at least 1/4 wavelength from any surrounding metal or obstructions.

I then cut a length of shrink tubing a few inches longer than the whip, and shrunk one end down for about half an inch. This will keep it from sliding all the way down past the tip, because it will be on and off the whip quite a few times. Slide the shrink tubing over the whip, and test the SWR again. You may have to remove a good bit if twin lead to get the SWR back down, it really depends on the shrink tubing you are using. Just like putting one of these j-poles in PVC, the shrink tubing changes the velocity factor of the antenna system. You will have to keep working at it until you reach a SWR minimum that you are happy with. With the j-pole taped to the shaft starting at the top of the stick, the bottom end and the feed point are both more than 1/4 wavelength from the mount, so that parameter is satisfied.

Once the SWR is good with the shrink installed, use a heat gun, hair dryer or a burner on your kitchen stove to shrink the tubing tight over the j-pole. You don't want to melt or burn it, so watch it closely. As you get toward the bottom half of the antenna, start paying attention to the way the coax is routed down the shaft. You can make it nice and neat by keeping it straight as you shrink it into place. I trimmed the shrink even with the top of the shaft, and let it overlap the metal ferrule at the
bottom a bit before trimming there. I also found that if I put an extra layer of shrink at the tip, the original Firestik rubber cap fit snugly. Lastly, I applied an extra layer of shrink at the bottom to reinforce where the coax exits the shrink tubing.

Next, you have to work out the mounting. The whip is relatively unyielding, so mounting it on the roof was out, as the cab roof of my truck is about 7' high and the antenna would have hit most overpasses. Although it is a compromise, I decided on the rear bumper. I bolted a 1/2" galvanized floor flange to the bumper, and screwed
a 2' length of galvanized pipe into that, (see 1st picture below).



Next came a 1/2" threaded coupling, and into that I installed a stainless steel 1/2" x 1/8-27 NPT reducing bushing. This I tapped out to 3/8-24 NF machine thread. Although you could screw the whip straight into this, I chose to use a Hustler QD-2 antenna quick-disconnect so that I could easily lay the whip down if I needed to get into any low spots. This arrangement puts the QD-2 right about the height of the top of my bed, which in turn places the bottom of the antenna element better than 24" from the bed, easily satisfying the 1/4 wave separation requirement (see 2nd picture below).

I used a 12' length of coax for this project, so I was able to take 5 turns about 5" in diameter to form an RF choke at the base of the whip (see 3rd picture below).

This really seems to help in keeping stray RF out of the system. It does look a bit odd, however. The coax is then coupled to a run of RG-8X up to the transceiver in the cab. OVERVIEW:Viewing the entire assembly, the pipe mount is just over 2 feet tall. The whip on top of that is about 7 feet.  A 300-ohm twinlead j-pole comes in at a few inches under 5'. The top end of the the twinlead starts about 1.5" down from the tip of the fiberglass shaft, and is taped to it. This leaves about 2' of space between the shorted end of the j-pole and the threaded end of the whip - plenty of space. The shaft is "top-loaded" this way for added height, and to provide free space away from the metal of the truck body.I live in a pretty hilly region of Texas, and with the added height that the fiberglass whip gives, plus being on top of the pipe base, it gives me the extra height above ground which enables me to consistantly carry out QSO's with base stations 50 miles distant........on simplex! Granted, it is down in the S1-S3 range, but the signals were nearly full quieting. All reports I have received on the antenna system have been excellent.If you are looking for something different in a mobile antenna, and have the space to run it, I'd give the N5HII "J-Stick" a try. Antenna Parts List 5' of 300 ohm TV twin lead 7' fiberglass wound antenna (aka "Firestik" or the like) Non-metal shaft12' RG-58 or like coax, with connector
7' length of heat shrink tubing, ¾" x 3/8" Solder and iron, hobby knife, electrical tape
Mount Parts List 1 ea. 1/2" NPT floor flange, galvanized 
1/2" NPT v 2' steel pipe, galvanized 1/2" NPT steel coupling, galvanized1/2" NPT x 1/8-27 NPT stainless steel reducing bushing Hustler QD-2 antenna quick disconnect 3/8" x 24 NF tap hardware to mount flange to vehicle


 73

Mark ~ N5HII
Email Mark for questions ~ n5hii at arrl dot net

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