Robert: Yes, most of the radiation from a conductor originates in the
high current section(s) of the conductor, and for a half-wave dipole,
that's the center, low impedance part. The sag will lower the center,
ergo the "gain" will decrease. Whether or not it's enough to be
noticeable is questionable however, and may be off-set by the losses in
transforming the balanced line to unbalanced and the impedance
transformation required. At some point in all this discussion, you will
find yourself trying to pick the fly poop out of the pepper [military
expression which I've cleaned up a little for this forum].
Related: The voltage/current distribution on a conductor is determined
*only* by the length of the conductor measured in wavelengths. It
doesn't matter how or where you inject the RF current. A Buddipole in a
horizontal configuration is off-center fed because it is inherently
physically short and low, and the center impedance is also low ...
~20-30 ohms on 20 meters. Moving the feed point out toward one end
raises the impedance seen by the 50 ohm transmission line. It also
unbalances the entire system leading to undesirable current on the outer
surface of the coax shield conductor.
And, to the original subject I assigned to this thread, how many
remember the Windom feed that Novices, who couldn't afford transmission
line, used in the 50's. Definitely "Less Than Perfect" but there are
QSO's in my log using it.
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 12/8/2018 7:03 PM, Robert G Strickland wrote:
Ron...
Would such an antenna cut for 80m, fed with ladder-line, and used on
40m, be a better performer on either band than an 80-40m fan dipole
fed with 72ohm coax? Leaving all other extraneous but influencing
parameters aside. I have the second antenna; the weight of all that
wire and the coax with a ferrite balun results in a significant sag.
I'm wondering if the first antenna, lighter and higher in the air,
would perform better? Thanks.
...robert
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
