Re: Quarter-wave whip earth plane

Joerg <news@analogconsultants.com> wrote:

[...]

looking at the
rear doors I notice very sturdy hinges where the sections on the side of
the van will have a solid chassis contact. That is where hams sometimes
mount antennas over here, especially big HF antennas. Not only would you
solve the grounding issue but you'd also have a solid mounting point
without drilling into the vehicle.

That's a brilliant idea which had never crossed my mind.  I had already
been thinking along the lines of tubes extending telescopically sideways
from  inside the roof bars as supports for vertical poles for public
address loudspeakers but I couldn't think of an easy way to hold the
bottom of the pole to stop it tilting.  Universal mounts on the door
hinges would be much better.

For example, you could get another of those hinges from a vehicle
junkyard, have someone weld a piece of steel to it and then mount the
antenna on that. If you ever sell the van you could mount the hinge you
took off.

I have never seen or heard of one of these being scrapped in the UK,
they are all exported to third-world counties and converted into lorries
and buses.  (The engine and transmission is reputed to outlast three
sets of bodywork.)  Perhaps a hole could be drilled through the hinge
strap to take a bolt - that could be removed later and the hole might
not be noticed.  I can do my own welding, but that is much harder to
disguise.

One thing you might consider is to drill or machine three big holes into
the steel plate and sink the magnets into it so they are flush with the
bottom surface. That way the whole steel plate could make surface
contact with the roof (with a thin protective plastic layer in between,
of course). That should increase the capacitance substantially.

 
That's an idea, I won't be able to do it with the existing plate, but I
do have a bigger piece that might work.  My lathe only has 9" radius
swing (with the bed gapped), so I might have to trepan the holes
instead.
 

 
Or maybe ask a friend who has a bigger lathe.

I have a contact in a heavy engineering factory (I sorted out one of
their CNC machines a few years ago) but another approach might be to
drill a lot of smaller holes and buy a lot of smaller magnets.  A sheet
of polythene damp-proof course material or adhesive-backed neoprene
sheet across the whole underside would prevent scratching


--
~ Liz Tuddenham ~
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www.poppyrecords.co.uk