Tarheel Model 200 Screwdriver Antenna - Fixed

I have been having some SWR problems with my Model 200 Screwdriver antenna, made by Tarheel Antennas. It is an older one, I believe I got mine in 2002. For the most part it has been a great antenna. I have used it for portable, mobile, as well as base use at some point in time or another. The versatility of a Screwdriver antenna makes them hard to beat in a lot of situations.

I suspected the SWR fluctuations were due to a bad connection some where. The first place I checked was the safety spring on the whip. I like to use the 3/8"x24 spring shock absorbers on all of my antennas with that style mount for some safety from impacts. As part of the design there is a wire that runs up the center of the springs (it doesn't matter what size, large or small, they all have it) so that when the whip bends over the stretching of the spring doesn't act like an inductor changing the resonance of the antenna - the wire shorts it out to maintain resonance. After having a spring fail in the past I checked this first. Sure enough, the wire strands inside were corroded and all but one strand was broken.

So I pulled the spring off and directly screwed the whip in to the top of the antenna. No luck. The SWR still went all over the place going down the road. Since we had a pretty good winter this year with lots of snow I figured all the subsequent road salt might be playing part of the problem by getting up into the coil. So I figured I had a bit bigger problem on my hands than replacing (or just removing) the spring.

I decided to take the antenna apart to check it out. I have had this one apart several times in the past so I knew how to do it, it really is a pretty simply constructed mechanism.



The first step is to raise the antenna all the way up to expose the whole coil. Then disconnect the shield from the top of the coil and slide it down. This exposes the coil. To access the entire coil you need to pull off the machined top of the base by loosening three set screws. This part has copper finger stock inside and is what makes the electrical connection between the coil and the base.



If you look above my fingers inside the part you can see the edges of the copper finger stock strip inside. This needs to be cleaned as well as the coil itself.

I didn't really have to do this as it turned out, but I pulled the guts out of the antenna. I was trying to get the mounting stud off the top so I could pull the PVC cap off to get the machined contact off the coil to clean it. The stud is ON THERE FOR GOOD. I don't know how they got it on that tight, but I would have ruined the antenna if I tried any harder to unscrew it. So I just left it in place and improvised.



For cleaning I used strips of a thin cardboard box. I wanted something I could rub the parts with that was mildly abrasive but also stiff and strong enough to not tear. Paper is a good contact cleaner - I learned that trick from some old CW operators for cleaning key contacts. I figured paper would work just as well here, but the cardboard is one better as it is thick and won't tear like paper.



Here you can see one of the strips I used. Note the black stuff on the cardboard. That is just from the finger stock surfaces!!! That isn't the strip I used for the rest of the coil.

After scrubbing down the coil and the contact I put it all back together. Surprisingly, the SWR still was fluctuating! I thought I had tried everything. The coax is sealed real well (with my favorite PlastiDip weather proofing treatment) so I didn't think that would be an issue. Though, I would probably have sliced it open just to inspect it. A can of PlastiDip is only $6 so even if I got one use out of it (which, if you seal up the cap REAL well with tape after you open it the can will last a while) it is pretty inexpensive stuff (as opposed to CoaxSeal).

After pondering what to do I got one more idea:



The screwdriver antennas are so big that the base alone is not strong enough to support it. There is a second support up off the base for two points of attachment (the ring support on the antenna for the mount is shown here). Originally, the base had a plastic strip around this secondary support hole on the mount. After a few months it wore through so I wrapped this part of the antenna that contacts the mount with electrical tape, as seen here.

Well, I figured the electrical tape was worn through. I couldn't really tell too easily so I figured it wouldn't hurt to add more to it anyway. Then the antenna started working! Only, I had put too much tape on and I couldn't tighten the antenna down all the way - the tape made it too tight in the hole. So after driving around this morning I removed some of the tape and got the antenna all the way down in the mount and it worked all the way home! I talked with Ernie VA6EJR in Alberta on 17 meters for a good while - with a solid SWR less than 1.1:1 the whole way!

If I had just gone to the ring and checked the tape the first time I probably would have had this antenna back up and running in no time. However, I am glad I pulled the whole antenna apart and took some time to inspect and clean the contact and coil. This antenna is in daily use on my truck, and quite frankly I am surprised it has held up this well for so long! Tarheel Antennas really are good antennas, just as with anything else they do need a little maintenance.