[TowerTalk] 30M with a C3....

[w8ji.tom]

Hi Tom and all,

> At half size, the reduced size accounts for several dB less efficienty,
> but
> it did work.  The G5RV represents 70% of a half-wavelength on it's
> lowest frequency which is more efficient, probably on the order of 2 to
> 3 dB down from a full size dipole.

Amazing as it seems, the size reduction results in almost no measurable
performance loss except the (sometimes small) additional loss caused by
increased current on the feedline.

There is a popular, but incorrect, assumption that current that would
otherwise radiate moves out of the antenna and down in the feedline when
the antenna is shortened. In reality, current in the antenna increases as
the length is reduced. The feedline current increases because of the
increased antenna current, but never is larger than the current in the
antenna in this situation.

That can be confirmed with an amp meter, or by modeling the antenna and
looking at currents.

The increased current does increase feedline loss, but with heavy
conductors in the transmission line loss is small. Unless the antenna is
fed with a long length of small coax, losses are actually very low.
I'm sure the same would apply to other systems if the feeder is low loss up
to the matching system.

73 Tom


--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm