Mobile Antenna Experiment - Whip and LDG Z-11Pro

This is something I have been wanting to do for a while and I just got around to doing it!



My screwdriver antenna, a Tarheel model 200 (the older model, mine is 8 years old - the new ones are made even better) is having some tuning problems. I need to take it apart and clean the coil as well as the finger stock on the top of the base which contacts the coil. My SWR fluctuates all over the place going down the road. That's not to talk bad about it - the antenna has LOTS of miles on it and we just came out of a pretty bad Ohio winter with lots of road salt.

Since the screwdriver is off the truck I figured I would use that as an excuse to work on my whip and tuner experiment. The first task was making the antenna mount. I did this just like I did on the other side for my CB antenna - I cut a 2x4 down to fit inside the stake hole and screwed a metal plate on top which is what the antenna mount attaches to, off to the side of the truck. The CB antenna has worked flawlessly for years.


The new antenna mount. Note the next paragraph.


This is the old CB antenna mount. This one has MANY miles on it, as does the screwdriver. They are on the truck nearly 100% of the time. Note the thick base under the spring - I machined that from stainless steel.

I had a broken tri-mag mount, one of the old MFJ's with the 5" magnets and 1/4" aluminum frame. Since it was toast already I took it apart and stole the top bar - the one that had the original 3/8"x24 mount bolted to it. The hole was already there - all I had to do was drill through the end to screw it to my wood block. The thick bar makes it hard to get the cap to latch shut. I will probably change it at some point.

After that - it was on to hooking up the wires. I decided to connect the ground to my screwdriver antenna mount. It was already grounded very well and it was easy to attach my tuner ground wire to one of the mounting bolts. The wire between the tuner and the antenna just plugs in to the center pin of the SO-239. I tinned the wire and left a blob of solder on the end just big enough to press fit in the center pin (not too tight). For my random wire antenna at the house I use an old PL-259 I melted off of a bad cable. I soldered 14g solid wire to the center pin, filled the body with epoxy to lock the wire in, and put a spade connector on the other side. This makes it a bit easier to work with, but I didn't have another junk PL-259 to use this time.


Note the tuner and the battery (black box hiding under the corner of the rug). I didn't feel like running the power cable for this experiment as well so I just threw an SLA back there.


The whip I am currently using is a 10m hamstick with a couple of Buddipole arms on the bottom for some extra length (see the first picture - the blue poles on the bottom are the Buddipole arms). The good thing with a non-resonant whip antenna is you can toss what ever you want in the air and get the tuner to do the rest. Generally the longer it is the more efficient it is on lower frequencies. For stationary use I have a 9' or so telescoping whip to put on top of the hamstick base (in place of the stinger). I have done that for more efficient operation on 40 meters on the screwdriver sitting in the driveway and it worked pretty good! I had about 15' of whip above the coil, but hey I got out.

So how does the antenna perform? Well, I had a nice conversation with Jeff G4SOF in England all the way home from work this evening on 17 meters. I was running 50 watts. I guess that's not too bad.

Now the real scoop -

The antenna loads up on 40-6 meters with the tuner. However, if I run a carrier at anything over 10 watts the SWR starts jumping around all over the place (key down CW). If I am running SSB I can get up to 100. I was hesitant to run much more than 50 watts at the time I spoke with Jeff because when I tuned up I did so on CW and the SWR went haywire with much power. However, after we signed I played around with the power and called CQ a few times at 100 watts SSB and never saw the SWR jump.

Running the tuner in this configuration places high voltage between the tuner and the base of the antenna. The wire I am using to connect to the two is not high voltage so I am probably getting some arcing. SSB has such a low percentage of power compared to CW that only on voice peaks do I hit whatever I set my output power to. CW is full power with every tap of the key, which means a much higher chance of arcing.

At some point in the future I will play around with a few different things - tuner placement (perhaps outside of the bed) as well as swapping the wire out for some high voltage stuff. My goal is to be able to run 40m CW. The thick bar for the mount also makes it hard to get the cap to latch shut. I will probably change it at some point to some thinner gauge steel, like the CB antenna mount is.

Here are some more pictures of the install.


Ahh. My favorite weather proofing - PlastiDip!!


I wrapped the wire here with electrical tape trying to up the breakdown voltage. I don't know how well it worked. If I key up on high power I still get the SWR going wild. What irritates me is when the tuner knows it is at a good match then when I kick the power up it goes out of whack. The tuner re-initiates a full tune cycle and the match it just had is gone. RF can be screwy sometimes.