With mobile verticals what is ALWAYS forgotten about is that the car
body is just as much a part of the radiating system as the antenna.

The body is just the lower half of a somewhat off-centre-fed,
mishaped, vertical dipole.

It is ridiculous to describe its operation in such laymen's terms, but
the body radiates as much useful power as the antenna itself. And it
is fed with coax whereas, according to perfectionists, to prevent
radiation from the feedline, it ought to be off-centre fed with
450-ohm ladderline. But from wherever it supposedly comes radiation is
never wasted.

I've often thought of modelling a mobile loaded whip in a computer
program. Input data would include body dimensions and height above
ground. With a lot of patience you could do it with an EZNEC type of
program.
----
Reg, G4FGQ

I guess you could buy one of those square cars like the Scion to make the
modeling easier.

"Reg Edwards" wrote in message
...
With mobile verticals what is ALWAYS forgotten about is that the car

In article ,
Reg Edwards g4fgq,regp@ZZZbtinternet,com wrote:

With mobile verticals what is ALWAYS forgotten about is that the car
body is just as much a part of the radiating system as the antenna.

The body is just the lower half of a somewhat off-centre-fed,
mishaped, vertical dipole.

Some people refer to mobile verticals as "short tuned counterpoises,
working with a large untuned radiator".

I've often thought of modelling a mobile loaded whip in a computer
program. Input data would include body dimensions and height above
ground. With a lot of patience you could do it with an EZNEC type of
program.

There are probably some not-quite-obvious gotchas to be considered.

I've observed that a significant number of vehicles (e.g. my Ford
Aerostar minivan) don't weld the body panels to the frame. Instead,
the side panels and roof are _glued_ to the framework using a
structural adhesive, and there's no DC connection at these points...
just a capacitive one (probably with high capacitive reactance).
There's DC continuity in some places, but not at all contact points.

Depending on how the vertical is grounded to the vehicle (to the
panels, to the frame, or to both), the RF "ground" currents are likely
to vary quite a bit.

Similar issues are likely to exist in recent-model cars which have a
lot of fiberglass or other composite-plastic panels and structure.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Wed, 08 Jun 2005 17:57:21 -0000, (Dave Platt)
wrote:


Similar issues are likely to exist in recent-model cars which have a
lot of fiberglass or other composite-plastic panels and structure.

Back in the good old days, I was the proud owner of a 1956 Corvette,
one of only 3467 built and along with the '57s, the prettiest ones
ever buit. (damn I wish I had that car back). As are all Corvettes,
it was fiberglass.

The soft top was stored under a flip up hatch behind the seats and
there were two toggle clamps that secured the rear of the top when it
was up. These penetrated the hatch cover so that it was possible to
snake a vertical whip through them. I used a 17" aluminum
transcription disk (common in broadcast stations of the day) with the
coating stripped off for a ground plane under the hatch.

Best DX using a Heathkit "Twoer" was from the driveway of a friend in
Tempe, AZ back to another friend in Tucson; about 100 miles.

This wasn't long after QST magazine had breathlessly reported that the
"difficult path" between Tucson and Phoenix had been bridged.

In article ,
Wes Stewart wrote:

On Wed, 08 Jun 2005 17:57:21 -0000, (Dave Platt)
wrote:


Similar issues are likely to exist in recent-model cars which have a
lot of fiberglass or other composite-plastic panels and structure.

Back in the good old days, I was the proud owner of a 1956 Corvette,
one of only 3467 built and along with the '57s, the prettiest ones
ever buit. (damn I wish I had that car back). As are all Corvettes,
it was fiberglass.

all corvettes were not fiberglass!





The soft top was stored under a flip up hatch behind the seats and
there were two toggle clamps that secured the rear of the top when it
was up. These penetrated the hatch cover so that it was possible to
snake a vertical whip through them. I used a 17" aluminum
transcription disk (common in broadcast stations of the day) with the
coating stripped off for a ground plane under the hatch.

Best DX using a Heathkit "Twoer" was from the driveway of a friend in
Tempe, AZ back to another friend in Tucson; about 100 miles.

This wasn't long after QST magazine had breathlessly reported that the
"difficult path" between Tucson and Phoenix had been bridged.

On Fri, 10 Jun 2005 11:19:29 GMT, ml wrote:

In article ,
Wes Stewart wrote:

On Wed, 08 Jun 2005 17:57:21 -0000, (Dave Platt)
wrote:


Similar issues are likely to exist in recent-model cars which have a
lot of fiberglass or other composite-plastic panels and structure.

Back in the good old days, I was the proud owner of a 1956 Corvette,
one of only 3467 built and along with the '57s, the prettiest ones
ever buit. (damn I wish I had that car back). As are all Corvettes,
it was fiberglass.

all corvettes were not fiberglass!
^^^^^^^^^^^^^^^^^^^^^^^^^

OK, I'm calling bull**** on this one. What production Corvette was
not GRP (glass reinforced polyester) or other non-metallic composite?

R






The soft top was stored under a flip up hatch behind the seats and
there were two toggle clamps that secured the rear of the top when it
was up. These penetrated the hatch cover so that it was possible to
snake a vertical whip through them. I used a 17" aluminum
transcription disk (common in broadcast stations of the day) with the
coating stripped off for a ground plane under the hatch.

Best DX using a Heathkit "Twoer" was from the driveway of a friend in
Tempe, AZ back to another friend in Tucson; about 100 miles.

This wasn't long after QST magazine had breathlessly reported that the
"difficult path" between Tucson and Phoenix had been bridged.

Russ wrote:

OK, I'm calling bull**** on this one. What production Corvette was
not GRP (glass reinforced polyester) or other non-metallic composite?


I know very little about this, but a few months ago I was fascinated by
a half hour program about the history of the Corvette on public TV.
(It's one of a series.) Turns out that the first couple of 'vettes
weren't muscle cars at all, but gutless wonders with a small engine and
two-speed automatic transmission -- it took a while to evolve. I don't
recall for sure, but think it's likely those were metal.

Roy Lewallen, W7EL

Roy:

You are right on target, I would have to ask my dad, but back around
1960 he had a 1956 vet (if I remember the year correctly--it was a 4
speed--again, if I remember correctly--that is really pressing my memory
though--could easily be wrong)... it was an all aluminum body (sure
about that), had a big engine, stick shift, and he never got out of
second gear in town... however, it did NOT seem gutless to me... nor him
as I remember it... he could have had a larger engine placed it it
though... he had it for many years... sold it in the 70's for way more
than he bought it for!!! ... he claims it was the only car he ever got
a ticket in, and more than one...

John

"Roy Lewallen" wrote in message
...
Russ wrote:

OK, I'm calling bull**** on this one. What production Corvette was
not GRP (glass reinforced polyester) or other non-metallic composite?


I know very little about this, but a few months ago I was fascinated
by a half hour program about the history of the Corvette on public TV.
(It's one of a series.) Turns out that the first couple of 'vettes
weren't muscle cars at all, but gutless wonders with a small engine
and two-speed automatic transmission -- it took a while to evolve. I
don't recall for sure, but think it's likely those were metal.

Roy Lewallen, W7EL

Roy Lewallen wrote:
Turns out that the first couple of 'vettes
weren't muscle cars at all, but gutless wonders with a small engine and
two-speed automatic transmission -- it took a while to evolve. I don't
recall for sure, but think it's likely those were metal.

Don't know about the body but it had virtually the same 6 cyl
engine and transmission as my uncle's 1955 Chevy Bel Aire.
Chevy introduced the V8 (350 in^3?) in 1956 and that's when
it went into the Corvette and into all those Chevys that broke
all the records that year.
--
73, Cecil http://www.qsl.net/w5dxp

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Reg Edwards wrote:
With mobile verticals what is ALWAYS forgotten about is that the car
body is just as much a part of the radiating system as the antenna.

I've always considered the vehicle body as a funny looking
large diameter elevated radial. :-)
--
73, Cecil http://www.qsl.net/w5dxp

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