RadioBanter - View Single Post

March 23rd 06, 01:43 PM posted to rec.radio.amateur.antenna

wrote:
You claim a bug cather coil has "an electrical length at 4MHz of ~60
degrees". That concept is easily proven false, just like the claim a
short loaded antenna is "90-degree resonant". Both can be shown to be
nonsense pictures of what is happening.

Well, I've been challenging you to do just that for weeks now and
so far, nothing. Please note the contradiction between your statement
above which says an antenna doesn't have to be 90 degrees long to be
resonant and your statement below which says it does. Would you please
make up your mind?

Assume I have a 30 degree long antenna. If the loading inductor is 60
electrical degrees long, I could move it anyplace in that antenna and
have a 90 degree long antenna.

This again demonstrates your misconceptions. Please pay attention
this time.

When my 75m bugcatcher coil is configured as a base-loaded coil
with a 7 foot whip, it occupies ~60 degrees of antenna. The 7
foot whip occupies ~10 degrees of the antenna. The total length
is only ~70 degrees, not 90 degrees. That 90 degrees is just your
strawman and you even contradicted yourself above.

The antenna doesn't have to be 90 degrees long. What has to
happen is for (Vfor+Vref)/(Ifor+Iref) to be resistive at the
feedpoint. There are many possibilities for that in antennas
not 90 degrees long. I gave one such example possibility
weeks ago. Perhaps you missed it.

I haven't measured the number of degrees occupied by a center-
loaded 75m bugcatcher coil. Since the inductance of the
center-loaded coil must be increased when moved from the base
to the center, it would occupy more of the antenna at the center
than it does at the base for the same resonant frequency.

The 70uH 75m bugcatcher coil occupies ~60 degrees when installed
at the base.

For the same resonant frequency and same length for the rest of
the antenna, a center-loaded coil would need about double that
reactance, making it about 1.4 times the size of the base-loaded
coil. So I would estimate that the center-loaded coil is occupying
~80 degrees of the antenna, much closer to a total of 90 degrees
than the base-loaded version.
--
73, Cecil http://www.qsl.net/w5dxp