RadioBanter - View Single Post - Dual-Z0 Stubs

Cecil Moore[_2_] · May 8th 09, 08:24 PM posted to rec.radio.amateur.antenna

wrote:
1) Cecil: I believe I understand how the Corum transmission line model
accounts nicely for the reduced current at the top of the coil. Does
it also account for the slight increase in current a short way from
the bottom?

I will say, apparently not. The Corum equations are stated
to be plus or minus 10 percent. The current increase in the
coil appears to be about 10%.

Typically, the current increases from a normalized 1.0 at
the bottom of the coil to about 1.1 close to the middle
and then falls off from there to 0.8 or so. Empirically,
it seems that one can take the rise in current, i.e. 0.1,
from the bottom of the coil to the middle of the coil and
subtract that value from the current at the top of the
coil to compensate mathematically for the curve not being
a pure cosine curve because of end-effects of the coil.

Example: Given a coil with a current of 1.0 at the bottom,
1.1 at the midpoint, and 0.8 at the top. It appears that
the ARCCOS(0.8-0.1) = ARCCOS(0.7) may yield an approximation
for the delay in degrees through the coil, i.e. ARCCOS(0.7)
equals ~45 degrees.

This makes sense to me since the current profile through
the coil is obviously not a pure cosine wave. It is obviously
distorted by the turn-to-turn coupling of the fields. But
just as obviously, this is an empirical curve-fitting technique
as used by Drs. Corum.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com