Posted by
Michael Babineau VE3WMB on
Dec 09, 2005; 1:51am
URL: http://elecraft.85.s1.nabble.com/Clever-antenna-tuning-ideas-wanted-tp384403p384404.html
Vic K2VCO <
[hidden email]> wrote :
> I would like to use it on 80m and 30m as well. My first try was to
> simply use the KAT100 to tune it. It tunes fine on both bands (1:1 at
> the rig), but results are fair-to-poor on 30 and poor-to-worthless on
> 80.
Can you clarify are the radials elevated above ground or are they on or
below the ground ? It sounds like they are tuned so my guess is
elevated?
>
> On 30m, the coax losses are reasonable (the SWR on the coax is about 8
> to 1, but it's very short). I suspect the problem is that the radial
> ground system is very poor on this band (on the other hand, the long
> vertical radiator should provide a slight amount of gain). So I may
> try
> paralleling a set of radials tuned for 30m. They will also be short,
> but resonated with a coil or stub. Does this sound like a good
> analysis/solution?
I suspect that this would help. You could also just try a single
elevated
tuned radial for 30m to make it into an L antenna with some
directionality
in the direction of the radial.
>
> On 80m, it's more complicated. The ground system is terrible, the
> radiation resistance of the vertical very low, and the SWR and losses
> on
> the coax very high. No wonder it's a dummy load! I guess the way to
> deal with it is to add more tuned radials in parallel and a switchable
> base network, but I would like to avoid any more control wires that
> have
> to go through my lightning suppression panel (I can't pass DC through
> the coax, either). Does anyone have any suggestions?
>
Well, one trick to put this sort of antenna on 80 is to make it into
an inverted
L by running a horizontal (or nearly horizontal) wire off the top of
the antenna.
Since it doesn't sound like it is practical to switch the wire maybe
you could
add an 80M trap and enough wire to get it close to resonance on 80m.
I'm thinking something like the Unadilla traps
(
http://www.unadilla.com/traps.htm).
You could always tack the second of the pair of traps to the single 30m
tuned
radial I suggested above and more wire on the other side of the trap to
make it
a dual-band radial on 30m / 80. If you don't have space to run in in a
straight
line bend it as necessary to make it fit your lot.
Michael VE3WMB
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