I see this a lot - need to get the elevated radials up xx feet or whatever.
But I don't know how to square that with the N6BT QEX data which shows a
improvement in efficiency as the radial is lifted up just slightly from the
ground (per QEX Mar/Apr 2012 page 39, figure 16, it's 0.0005 WL approx) -
with the slope of improvement flattening out beyond that.
Either the QEX data is wrong, or it's not applicable for some reason in the
special case of a 4-square (the article is about a single vertical with
elevated radials), or the claims of "moving the radials up made a big
difference" are subjective.
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
-----Original Message-----
From: Jim Brown
Sent: Friday, September 23, 2016 1:46 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] 4 square for 80
On Fri,9/23/2016 11:15 AM, RT Clay wrote:
In my opinion, if you are height limited, you want to stay away from
elevated radials. If you elevate your radials, you are giving up valuable
vertical distance which will further lower the feedpoint Z and increase
ground losses.
Excellent post, Tor. I'm not so sure that I agree with this paragraph
though. While elevating radials DOES reduce the effective height of the
radiator, and thus radiation resistance, elevating radials reduces
ground losses for the same number of radials. In essence, efficiency is
the voltage divider ratio between Rr and Rg + Rr, where Rr is the
radiation resistance and Rg is the ground loss. So it can be a tradeoff,
depending on what's practical at your QTH and how good your soil is.
Based on my 160M experience (4 radials up about 20 ft on a full size
vertical), I'd guess that 8 ft is pretty good for 80M. Those 4 radials
at 6 ft had way too much ground loss. On advice from N6BT, raising them
to 20 ft helped a lot. The feedpoint for those verticals is about 2-3 ft
high, and the radials rise quickly as they go away from the feedpoint in
a "gull wing" configuration.
73, Jim K9YC
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