[TowerTalk] Liberal Arts Question on Dipole Antennas

[Terry Conboy]

At 07:26 AM 2006-06-01, Lee K0WA wrote:
>   Is there an interaction between the tower...the 80 meter 
> antenna...the Vee to the east?

I put your 40m inverted vee and the adjacent 80m inverted vee into 
EZNEC (as I understand your layout), and as others have suggested, 
the 80m antenna does BAD things to the impedance of the 40m 
antenna.  How bad will depend on the tuning of the 80m antenna, the 
length of its coax, and what you have connected to the TX end of the 
80m feedline when you are using the 40m antenna.

Unless you need to operate 2 bands at once (which is scary, given the 
small spacing of the two antennas), you would probably be much better 
off putting both the 40 and 80m antennas in parallel on the same 
feedpoint.  I've done this for years with quite good 
results.  Depending on the spacing of the 40m and 80m wires, you may 
have to lengthen the 40m legs a bit to get resonance back in band.

You may also want to consider a balun at the feedpoint, since you can 
get a fair amount of current flowing on the coax shield and/or the 
tower, depending on their dimensions and where they find a path to ground.

Good luck,
Terry N6RY