On 3 May, 13:43, Spam Collector wrote:
While reading about antennas, I've been unable to find
answers to what I thought would be basic questions.
Most of what I've read seems to concentrate on narrow-
bandwith antennas, and even at that seems to concentrate
on what happens when lengths become shorter and ignores
the effects of longer lengths (for definitions of 'longer'
meaning 'much longer, as in many wavelengths longer).
The question is how various low-band antenna types
will perform at higher bands. For example, if I were
to run a wire around my property (about 300 x 500 feet),
giving me about 1600' of antenna length, I could run it
as a folded random wire (fed from one end), a loop (fed
from a corner or the middle of one side), or as a dipole
(if fed like the loop but cut on the oposite side).
What are the performance differences between the
three configurations, and is there a upper frequency
limit for practical use of them? For example, would it
work on say 2m or 70cm, where the antenna would be
hundreds of wavelengths long?

Thanks for any insight,
Frank
KE5MJZ

Frank, I did not adress your comment with respect to antennas of
narrow bandwidth. For receiving you have relatively unlimited
bandwidth because the antenna match is for extremely small power
transfer, the signal may become weaker but no damage is going to
occur. For transmitting it is a whole new ball game since the matching
syystem will have to transfer power in the order of a few watts or
even a kilowatt which is O.K. for a light bulb which is enclosed but
you really don't want the wires inside your transmitter to glow!
This is where matching the connection becomes important because tho
you can match the radio connection easily the antenna makes it harder
as you stray from the initial matching frequency such that wire
connections could easily glow and fail. Unfortunately it is very
difficult to design a antenna that will remain a close match to your
radio, this is just a fact of life. Usually you have to design an
antenna for a narrow band of frequencies which means more than one. In
your case where you have long wires it is possible to insert a black
box
that will provide a useable match across a large band of frequencies
but the other side of the coin is that antenna directivety is lost
since directivity is directly related to frequency.
As with all things there is no free lunch but it will sure provide a
lot of fun when playing with antennas and talking to the World.
Art
Art