On Tue, 15 Mar 2005 02:53:22 +0000, Dave Platt wrote:


Is that 58.5 inch figure a typo? Your NEC model says 51 inches, and
my quickie spreadsheet calculation says 50.9 inches for a 145 MHz
center of band.

Actually, the 51 you're seeing in the NEC model is probably the number of
segments. One end is at 0,0,36 and the other is at 0,0,94.5; so yes it's
really 58.5 inches. I came to this number by playing with the model until
the REAL component of the impedance got as close to 50 as I could get it.

I also wonder about the coil - it calculates out to be just over 1
microHenry, or about j910 ohms at 145 MHz. That seems like quite a
bit too much, based on jgboyles's posting earlier today indicating a
feedpoint Z of about 80-j300.

My model comes up with a feedpoint impedance of 5.4485E+01-j2.8560E+03

So I tried to build a coil with an inductive reactance to cancel that .. I
came up with 3.13 microhenries.

Is my model way off?????