[Towertalk] Gain wire antennas for 40M

Wes Cosand wz7i@arrl.net
Sun, 07 Jul 2002 12:53:45 -0400

For us tribander at 50 feet folks:

I would like to put up a unidirectional, horizontally polarized gain 
antenna to cover the US from here in W3 land.  I had decided to build a two 
element array with both elements driven because of the greater gain.  I 
would prefer an array that can be suspended from a single rope.  There are 
examples in the literature of a two element delta array with the second 
element driven by a 1/4 wavelength of ladder line.  One advantage of the 
ladder line is that the velocity factor of 0.95 allows physical spacing 
close to 0.25 wavelength.

But I am really confused about some elementary physics.  Won't the ladder 
line act exactly as a quarter wavelength transformer and step up the second 
loop's impedance of about 100 ohms to something like 2000 ohms?  Won't the 
resulting currents in the two elements be profoundly different?  Would the 
array work well enough to fool with?  Should I forget all of this and just 
put up a parasitic array with the lower gain?

Sorry I need to ask such a dumb question.  But there may be someone else 
that is confused by such matters as well.

Wes, WZ7I