Hi all,
Over at the Elecraft-KX io group, being QRP all the time we had this
discussion a while back and I wanted to repost a post I made with a
useful link, I think it is germane to this discussion:
--------------------------------------------------------------
https://elecraft-kx.groups.io/g/main/topic/90090191#72021
posted by Howard Hoyt - Mar 28, 2022 #72021
Hi all,
I thought I'd start this thread since some posts regarding antennas in
general were pretty much OT. Subjective reports we see in groups all
the time although great for expressing enthusiasm for ham radio
operation in general, carry little information others can use to
evaluate antenna performance.
Like many other hams I studied Maxwell's equations in EE school (too
many years ago), and they define the characteristics of electromagnetic
waves pretty thoroughly. I am sure modern antenna engineers utilize
them to perfect antenna designs and many hams may be talented enough to
use this approach. However this many years after Uni. I only have the
time and brain power to use more cookbook approaches, and like many
people I learn faster with visual aids.
With this in mind, and specifically regarding the oddly controversial
aspect of two-pole radiation (radiator and so-called counterpoise) I
wanted to share this YouTube video by Frank Rutter / K3AW:
https://www.youtube.com/watch?v=LEigIMS6bo4
He does a masterful job of presenting many aspects of antenna
performance using a 3 GHz model, which has a wavelength short enough to
allow the antenna and ground plane (counterpoise) to fit on a table for
demonstration. I highly recommend setting aside an hour, grabbing a
beverage and watching the entire 1:08:27 video, it may be the best
expenditure of your time this week. My single critique of the
demonstration is I wish he had a big meter to show the signal changes as
he changes the setup.
Relative to recent discussions regarding counterpoises here, Frank shows
how a lossy counterpoise (his model for earth) diminishes antenna
performance at the 10:00 mark. At the 30:00-minute mark he explains the
proliferation of stacked beams. At 1:03:00 he explains that an inverted
"L" can result in RF at the operating position, due to common-mode
currents. This Inverted "L" configuration resembles how many portable
end-fed antennas end up being deployed due to necessity. Also he
demonstrates how at commonly deployed heights they show a propensity for
high-angle radiation, good for close in to medium range communications,
not so much for DX.
Part of the value in Frank's demonstration is the relative, but direct
comparisons of the different antenna configurations in identical
locations. We do not have this luxury when operating from a hilltop or
at the beach, so we have to apply best practices to maximize results,
and in this way ideas from his demonstrations can be valuable to us.
As an additional note: I have learned a lot about designing antennas by
modeling them using EZNEC. After years selling and supporting the
software, Roy Lewallen / W7EL has given the package to us for free and
available here:
https://www.eznec.com
I highly recommend getting this software and learning to use it. If you
are truly interested in maximizing your antenna knowledge and
performance, it will be time well spent.
----------------------------------------------------------------------------------------
Anyone interested in the KX rigs or AX antennas should join our group,
over 6000 strong and growing.
Cheers & 73,
Howie / WA4PSC
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