On Monday, March 3, 2014 10:51:14 AM UTC-6, wrote:
That the metal under a mobile whip is
acting a lot more like a radial system, or even the ground itself,
than the other half of a physical dipole.

It depends on where it is connected to the vehicle. If connected near the center, the vehicle acts like two opposing radials and radiates mostly omnidirectional. If connected on the rear bumper, it can act like one radial. On my S10 with a rear bumper-mounted 17m hamstick, my signal was quite directional beaming toward the front of the vehicle. I would sit in the parking lot at Intel and aim my S10 mobile antenna system. I often gained an S-unit by aligning the vehicle with my contact. The fact that the S10 was a quarter wavelength long on 17m probably helped.
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73, Cecil, w5dxp.com

On Monday, March 3, 2014 12:52:37 PM UTC-6, W5DXP wrote:
On Monday, March 3, 2014 10:51:14 AM UTC-6, wrote:

That the metal under a mobile whip is

acting a lot more like a radial system, or even the ground itself,

than the other half of a physical dipole.



It depends on where it is connected to the vehicle. If connected near the center, the vehicle acts like two opposing radials and radiates mostly omnidirectional. If connected on the rear bumper, it can act like one radial. On my S10 with a rear bumper-mounted 17m hamstick, my signal was quite directional beaming toward the front of the vehicle. I would sit in the parking lot at Intel and aim my S10 mobile antenna system. I often gained an S-unit by aligning the vehicle with my contact. The fact that the S10 was a quarter wavelength long on 17m probably helped.

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73, Cecil, w5dxp.com

I bet it still acted like a vertical near the ground though, instead
of a dipole low to the ground. For instance, I bet the hamstick
did not require a drastic re-tuning when mounted near the rear vs
mounted in the center.

So I still think in your case, it was acting more like a near
ground mount vertical with a fat radial to the front, rather than a
whip at the rear with the car being the other half of a dipole.

And strictly speaking, I suppose it is. Sorta.. Kinda..

But it's not acting like one in operation. It's acting like any
other short vertical that is near the ground.

I saw a bit of directivity when I had the antenna on the rear trunk
lid of a Monte Carlo in much the same way as your S10. It favored
the forward direction a tad. I don't notice too much directivity
on the trucks, but both have the antenna near the center.

Anyway, as it applies to the tripod vertical, I wouldn't expect
running a braid to an RV as a very effective way to reduce ground
losses below the antenna. And the chances of it pairing up with
the RV to produce a usable "dipole" of sorts are not likely to
pan out. Ground losses will still be high below the whip, and
I bet the RV will more likely resemble a big pile of earth a few
feet away, than a viable radiating element. :/
Unfortunately, the big pile of pseudo earth will be in the wrong
location to be of much help to the tripod mounted whip.

On Tuesday, March 4, 2014 5:22:18 AM UTC-6, Jeff wrote:
Also do not neglect the (considerable) capacitance of the vehicle body
ground to the the real ground.

I was on the top uncovered story of a three-story parking garage made of concrete and steel and the weather was dry.
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73, Cecil, w5dxp.com

On Tuesday, March 4, 2014 10:19:49 AM UTC-6, W5DXP wrote:
On Tuesday, March 4, 2014 5:22:18 AM UTC-6, Jeff wrote:

Also do not neglect the (considerable) capacitance of the vehicle body

ground to the the real ground.



I was on the top uncovered story of a three-story parking garage made of concrete and steel and the weather was dry.

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73, Cecil, w5dxp.com

Makes sense to me. You had a 4 ft wide solid metal appx 1/4 wave
radial system in the forward direction. So what was below the truck
shouldn't have really mattered much. Or at least in that direction.
Which is the whole point of having a dense "radial" system below
a low vertical. And even more critical with a low short vertical.

His is a 7m fishing pole fed with a auto tuner. Would be short on
40 and 80. I bet adding a few top loading wires would help on those
bands, but that's probably out of the question if he can't string up
dipoles and such. Maybe make some "L" spokes to clamp on the top with
a hose clamp. A wire connecting the outer ends of the spokes would be
even better. Would improve the current distribution. Or could add a
center loading coil for 40 and 80. That would help if no top loading.