If the rig can't accept 5% uncertainty in the antenna feed Z and
resonance, its not going to work with ANY untuned antenna because they
can change that much from wind, ice, rain and perched birds.
The main benefit of the recommended lengths that I've seen is that the
feed impedance is mostly resistive, though low or high and easity fed
with either a series tuned link coupled tuner or a parallel tuned link
coupled tuner. That the recommended lengths of wire and feed don't
reflect highly reactive loads to the tuner. Using a simple wire on
multiple bands presupposes a tuner because of the wide range of resonant
impedances. An antenna needs traps, stubs, parallel wires, or lots of
resistive loading to present an impedance the modern fixed match solid
state rig over most of the HF bands. Even the leaky dummy load works
after a fashion if the situation requires instantaneous frequency change
with absolutely unskilled operators if one is willing to accept its
occasionally poor efficiency.
73, Jerry, K0CQ
On 11/29/2010 11:34 AM, Steve Hunt wrote:
I doubt the recommended lengths in that article are very useful.
Factor in an uncertainty of up to 5% to allow for variations in wire
velocity factor, further uncertainties due to the environment (ground
conditions etc), and plain errors because he has assumed that a wire
resonant at F will also be resonant at 2*F, 3*F, 4*F etc, and the
recommended "good lengths" become pretty meaningless.
Steve G3TXQ
On 29/11/2010 13:29, kf6e@mail.com wrote:
Here's a link to an article listing the best lengths to use for a random wire
antenna:
http://www.hamuniverse.com/randomwireantennalengths.html
I didn't measure mine; I just strung up some wire. I suspect you will have
better results if you use one of the lengths suggested in the article.
73,
Frank
KF6E
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