Re: Quarter-wave whip earth plane

In article <1r900dz.zmjlph1mxwv5uN%liz@poppyrecords.invalid.invalid>,
liz@poppyrecords.invalid.invalid says...

 

 
9ohms isn't much, 18ohms is. But yes, that extra 120pf in series with
the coax center will alter resonance which can be corrected by changing
the length of the whip.

 
I've made it from an assortment of light alloy tubes and rods (the rods
were machined down between centres on a large lathe so they can slide
into the tubes).  There's quite a lot of adjustment but I wonder how
much that will affect the terminating impedance of the co-ax (it can be
tuned to be resistive but it may not not necessarily be 50 ohms).
 
 

I don't see any "non-invasive" solution, assuming you don't even want a
pointy contact screw into the metal because maybe the van is fairly new.
That would also rule out sanding down the thickness of the paint :-)

 
It's not that new but it is 'tidy' and I would like to keep it that way.
It is also used as a 'stealth' camper, so the mounting has to be easily
removeable so as not to attract attention when parking up for the night.
 
 
 

You are probably overthinking it.  Just use a 1/4 wave whip and adjust
for lowest SWR.  should be close to 19 inches for 2 meters.  The
impedance is going to be about 36 ohms if a perfect ground plane. That
should be low enough not to burn out he finals of the transmitter and
the short coax with that low SWR wo't effect the range.