On 5/31/2011 5:40 PM, John S wrote:

A folded dipole is about 300 ohms. A half-wave shorted transmission line
is about 0 ohms. So, if you take a shorted half-wave transmission line
and spread the wires apart at the 1/4W point all the way to where it
becomes a folded dipole, it seems to me that the terminal resistance
will go from zero to 300 ohms and 50 ohms is in there somewhere.

I tried it in EZNEC and found that to be the case. I found that, if the
acute angle of the rhombus is about 51.5 degrees, then the terminal
resistance is about 50 ohms (adjust perimeter along with angle to get
50+j0).

As an aside, I found it time consuming to adjust angles and repeat the
source impedance test in EZNEC. So, I created an Excel spreadsheet where
I could simply input the perimeter, the acute angle, height above
ground, wire gauges, and number of segments and wrote a short VBA to
gather the spreadsheet results and create an EZNEC importable file.

Man, what a time saver.

73,
John