It's disappointing to see that people have gotten so many different
results modeling such a simple antenna with EZNEC.

Jerry's results are correct. You'll get slight variations with differing
segmentation and ground conductivity, by they won't be large differences.

I haven't followed through the article's math, but there's either a
computational error or something fundamentally wrong with the equations
to produce a value of j1776 for the antenna's reactance. The fact that
the author's reactance is just about twice what it should be points to a
likely error in computation.

Jerry, what the EZNEC result means is that you'd need a *total* of j881
ohms at the feedpoint to resonate the antenna. You could do this by
adding half the amount to each leg, or the total to one leg. Or, you
could move the coils out toward the end, but you'd then need more
inductance. Of course, you've still got a feedpoint resistance of about
11 ohms, plus coil resistance, to transform into something close enough
to 50 ohms to make your rig happy.

Roy Lewallen, W7EL

Jerry wrote:
October's QST has an article "Designing a Shortened Antenna" pp 28-32. It
gives an example of a shortened dipole for 40 meters at 7007 khz. Dipole
length of the half-sized dipole [p30 "a second example"] is 10.61 meters.
This is 20 feet off ground using #12 wire. The formulas give a solution of
XL= +j1776 ohms or an inductance of 40 microhenries at 30 degrees from each
leg.


I tried to simulate this antenna on EZNEC. A 10.61 meter antenna at 7007 khz
gives impedance =11.33 - j 881.2 ohms.

If EZNEC is correct wouldn t I need an inductance of +j881.2 on each leg of
the dipole, rather than +j1776?