Mobile Antenna Help

[Richard Arland, W3OSS]

I suppose you're wondering why I called this meeting!!

Actually, I am in need of a solution for my mobile HF antenna. I got talked 
into buying a High Sierra Sidekick screwdriver mobile antenna. It is 
extremely short (around 4 ft or so fully extended) but according to the 
folks at High Sierra, it is capable of 80-10M operation.

Now I realize that this is all manufacturer's hype but as we all know if you 
add enough capacitance and inductance in line with the antenna you can get 
it to  resonate almost anywhere. Radiation efficiency is something entirely 
different, and much harder to realize.

So, my situation is this: I have mounted the screwdriver antenna on the rear 
cross member of the roof rack on my wife's Nissan Pathfinder SUV. I have 
tried the antenna on various HF frequencies including 80 and 40 meters. 
While it does resonate, my 100 watts of RF output doesn't radiate 
efficiently.

I have thought about adding a ground plane to the roof rack in the form of 
copper or aluminum tape. In the days of slot cars, we  used copper tape 
which was positioned on each side of the "slot" in the track, and the motor 
inside the slot car had a set of pickups that would contact the copper 
strips providing voltage for the motor. Unfortunately, there is a definite 
shortage of this copper tape. About as close as I can come to it is the 
aluminum duct tape used to seal heating duct work. It is conductive and I 
was thinking of placing this on the UNDERSIDE of the roof rack and 
connecting each end of it to the ground portion of the antenna mount. I have 
anticipated adding a ground plane so I added some wing nuts to the lower 
portions of the antenna mount.

My general question to this group is: Do you think that this is a workable 
solution to the RF counterpoise problem on this mobile installation?? If 
not, don't be shy, tell me what you have used in the past (or present) that 
works for you. I am open to any and all suggestions (within reason, of 
course).

I was wandering around Home Depot yesterday and spied a bunch of 3/4 inch 
copper pipe used for plumbing. The thought immediately crossed my mind to 
use this, along with some 90 degree elbows to form a tubular counterpoise, 
paint it black (to match the roof rack) and place it on the underside of the 
roof rack, holding it in place with a few black plastic cable ties. The 
extra area might drastically improve the RF counterpoise and make the 
antenna perform as advertised. Just a thought.

Comments, anyone??

73 Rich W3OSS

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