Jim,
this will work. If you are going to put the wire lengths in series (33',
33', and 66') you will need a way to decouple the the relay coil wires
between the wire sections; two relays. The decoupling can be done with
parallel tuned LC circuits. As these are 'traps', simply dispense with the
relays and use the traps to make your three band antenna.
Dave WX7G
On Mon, Sep 28, 2009 at 1:22 PM, Jim Meehan <jmeehan@vpizza.org> wrote:
> I've mulling over a tree-supported wire inverted L for 40/80/160 meters.
> The vertical section would be supported by a high branch on a ~55' Monterey
> pine not too far from my house, and the horizontal section from there to
> another tree. Lots of radials of various lengths should be no problem.
>
> Originally I had thought to use traps to achieve multi-band operation, but
> then I started wondering about using relays to simply switch out the
> various
> segments. If I used two-conductor speaker wire or something similar as the
> radiator, I think the same wire could also carry DC to operate the relays.
> I'd use SPDT normally-closed relays. For operation on 160, no DC is
> applied
> -- both relays are closed, and the entire length of the inverted L is
> active. For operation on 80, +12V is applied, opening the "far" relay,
> cutting off both conductors of the 160 segment. For operation on 40, -12V
> is a applied, opening the "near" relay. This would be for 100 watts only,
> so I don't think I'd need anything too exotic for components.
>
> My hope is that it would have wider bandwidth than traps would allow, and
> be
> easier to construct and tune.
>
> Am I missing anything obvious? I did a little Googling and didn't find any
> designs like this.
>
> Also wondering about the bandwidth/hassle/cost tradeoff of using copper
> pipe
> or aluminum tubing for the vertical section. In this case, I'd run a wire
> up the center of the pipe to use as the 2nd conductor for the relay
> switching. I would put the pipe next to the tree, supporting it with some
> kind of standoffs attached to the trunk of the Monterey pine. Can I get
> the
> pipe far enough from the tree trunk to minimize interaction, but still
> close
> enough for standoffs to be practical? Is the bandwidth gain of pipe over
> wire enough to make this worthwhile?
>
> Thanks for your consideration,
>
> Jim Meehan, W6XE
> Oakland, CA
> _______________________________________________
> Topband mailing list
> Topband@contesting.com
> http://lists.contesting.com/mailman/listinfo/topband
>
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|