Tarheel Screwdriver Help (Hammies)

Tom,
sounds like grounding..Have you tried going to the battery direct?
I know when I have tuning problems I start with the grounding. and then the problem go away for a while..I'm having problem with my atas 120 But I know it is grounding problem. I had it fixed for about a week. I'm about ready to run a groundstrap from the atas 120 direct to the battery. I always find someplace on the run that the ground has developed a problem. So my advice is grounding.

 

Something else to remember on the Tarheel is to make sure the little raised strip on the antenna goes into one of the slots in the upper support clamp.

When that happens the plastic collar is compromised and the antenna grounds to the upper support clamp.

 

I forgot that PL259's go bad It has happened to me once or maybe twice. well good luck with your tarheel. Talk to you on HF.

 

I am considering becoming a driver. If I do I obviously won't have my own rig, I'll be an employee driver. Would there be a problem temp mounting my homebrew screwdriver antenna if I set it up to not scratch/damage anything? Thoughts?

 

A screwdriver antenna does not lend itself well to this kind of multiple mounting setup. Now IF this is going to be a temporary install where you will have the one truck of a specific time, it would probably be OK. BUT!
.......if you are thinking of some sort of "slipseat" arrangement for HF, I am afraid you are in for a letdown. I'm not saying it CAN'T be done: it is, however, a LOT of trouble and, if the user is not fully experienced in the ins and out of mobile HF, it will be a BIG disappointment. It is, too, very difficult to advise people from afar on this subject since the level of one's expertise will, naturally, vary from none to VERY knowledgeable.

Assuming a small knowledge level (and I apologize if I accidently "talk down" to you from your standpoint) since I don't know how much you know about HF mobile, one of the most important things about screwdriver antennas is feedpoint impedance since this is VERY important in getting your screwdriver to work AND understanding WHAT is going on with your setup. The FIRST thing I recommend is an MFJ ANTENNA ANALYZER. This device will save you MANY hours of wasted effort in setting up and using your screwdriver since it not only shows SWR, but displays the system impedance in a separate meter. It will readily show if your grounding is off, anything is loose (radical changes in SWR), or "funny" things going on as you drive down the road (such as one "good" reading at a given frequency, and all of a sudden everything is "screwy"---also ONE indication of bad connections or grounds. Also this device can be installed IN the truck and be used to "tune" your screwdriver precisely onto frequency as you go down the road. By installing a quality two-position switch, you can dial in a desired frequency, set the screwdriver to lowest SWR, switch back to the radio, and TALK. It gives you on-the-go, instant data on performance as you drive!

You should CLEAN your mount periodically down to the stud and get rid of any accumulated crud or rust. This will also cause your antenna to "act" funny after a period of time if you allow rust and corrosion to build up.

What kind of imedance matching device are you using? This can be a toroid, a coil with a jumper, or wander lead from a turn of the coil to ground (determined by the MFJ meter, or a simple small coil of small diameter wire (transformer wire) wound and inserted at the feedpoint from the mounting stud to ground. A SCREWDRIVER OR OTHER EFFICIENT HF MOBILE ANTENNA WILL NOT WORK WITHOUT IMPEDANCE MATCHING AT THE FEEDPOINT! If it DOES, it means that you have a sloppy, inefficient radiator and poor performance. Yes, there are reasons why this CAN be dont, but trust me, you do NOT want to do this. We won't go into this at this time. That's because it requires a lengthy discourse on complex impedance issues such as feedpoint resistance, coil resistance, and radiation resistance---all values of impedance.

One recommendation if you are determined to attempt multiple, temporary mountings of a screwdriver. I would use the simple little wire coil: about 21 turns of #22 transformer wire wound around a 1/4" dowel. You would need one for EACH truck you are going to use. And that is only ONE issue!!! You'll need a wired reversing switch (spring-loaded) for EACH truck. Then wire going to the battery from the switch, then to the antenna motor. (Are you SURE you want to try this?????)

Finally, here's what I think: It's going to be TOO much trouble. I would postpone the screwdriver until I could get into a permanent truck!!! I would simply get me a few hamsticks, and content myself with working 20 thru 10 Meters. That way you can mount a hamstick and operate a band or two, or when stationary and forget about Multiband HF mobile screwdrivers for the time being. Trust me. You MAY know more about HF mobile than I (but I doubt it), but unless you are willing to put in some REALLY imaginative sweat, "slipseating" HF mobile is more trouble than you may realize. Just MHO!

Good luck!

Gadfly

 

I am not an expert, but I have been doing HF mobile for a few years. I built 2 mobile antennas and the last one was a screwdriver. I found the plans on the yahoo screwdriver board. I know firsthand that it can be a pain in the neck but I've also had good luck with it. I didn't even use copper wire for the coil, just galvanized aluminum.

What I've had better luck with was my first HF mobile project. http://www.arrl.org/tis/info/pdf/0004033.pdf

Only $20 to build (6-20 meters). Two alligator clips to adjust and when you know where to clip you have a resonant antenna. I've worked Europe while driving across NJ in the afternoon. A very easy project and maybe someday I'll try to expand the band capabilities on it.

Dave N3ZJY

 

Sounds like a neat project and set-up! I wish you the best with it!

73

Gadfly