[TowerTalk] Combined Dipoles

[Jim Lux]

Bill Turner wrote:
> ORIGINAL MESSAGE:
> 
> On Tue, 15 Apr 2008 11:34:51 -0700 (PDT), Larry Boekeloo
> <lboekeloo at sbcglobal.net> wrote:
> 
>>  If I cut a dipole for 80 meters, 40 meters and 30 meters and connect them all to the same balun, would they at some point resonate on the correct frequencies with some tweaking?
> 
> ------------ REPLY FOLLOWS ------------
> 
> Yes, they will work very well indeed. My low-band antennas here are
> three inverted vees connected together just as you describe. I have 160,
> 80 and 40 meter antennas with the apex at 70 feet and the elements
> fanned out so they are about 20 feet apart at the ends. When I first put
> it up I expected a lot of tuning would be required because of
> interaction but there was remarkably little tweaking required. 
> 
> For anyone running high power, I highly recommend this instead of a
> trapped dipole/vee. Over the years I have smoked several traps that
> supposedly were rated for 1500 watts, but this antenna really is capable
> of full legal limit, brick on the key, no problem at all.
> 
> 73, Bill W6WRT



And, if you have a tuner that can tune, say, 2.5:1 or 3:1, you don't 
have to do any pruning at all.  They're dipoles, so they're pretty 
broadband, and if the resonant frequency drifts to 6.9 MHz from your 
7.15 that it would be without the other elements, the mismatch isn't all 
that big.  At that sort of mismatch, the line loss isn't as big a deal.

That way, if you're installing it somewhere that the surroundings are 
likely to change (e.g. it blows in the wind, and there's trees or a 
tower around), you don't have to worry about small shifts in fres.

BTW, after some hours of grinding the optimizer in 4nec2 I've not been 
able to find a set of lengths for 3-5 parallel dipoles that provides a 
good match on ALL HF hambands without a tuner.  It's possible that such 
a set doesn't exist.  (easy for the big 5, 10,15,20,40,80, though)

Jim, W6RMK