Mobile Antenna Help

Al Parker anchor at EC.RR.COM
Mon Feb 4 21:37:30 EST 2008

Hi Rich,
    Is the roof of the vehicle steel?  Can you ground to it & use it as the 
ground plane?  Does the mount of the antenna ground to the roof rack, and is 
the rack bonded to the roof?
    Sorry for questions & no answers, but maybe they'll stir some thoughts.
Al, W8UT
New Bern, NC

----- Original Message ----- 
From: "Richard Arland, W3OSS" <richard.arland at VERIZON.NET>
Sent: Monday, February 04, 2008 9:25 PM
Subject: [BOATANCHORS-TEMPE] Mobile Antenna Help

>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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