Jerry et all
My personal antenna FOR 160 was/is as follows
160M T:
60' Tall with with a 78' flattop. The "bottom" is at 7' ( so the
actual vertical element is 53') with three 90' radials at 7' spaced
pretty nearly in 60 degree increments ( 60, 120, 240). There is a tapped
inductor in series with the ground side (NOT the vertical side) of the
feed point used to resonate the whole thing . For the general approach
to loading and using non-resonant radials I was strongly influenced by
K5IU's work in Spring 1997 Communications Quarterly (google should
find you reprints of that) . The vertical is #14 bare stranded copper
and the radials are #10 Bare solid copper ( no magic on sizes etc just
what I happened to have on hand. Ezenec says this should be around 13
ohms at 1840 resonance ( with a 23uh series inductor) . In practice it
is closer to 25ohms at resonance with a about 17uh of inductance.
It is then matched with a 2:1 UNUN to 50 ohms. This antenna REALLY NEEDS
and uses a common mode choke at the feed point . This turned out to 10
to be ten FT-240-43 torroid's with 4 turns of coax through the batch,
lesser amounts of ferrite became quite hot.
After the smoke clears it all appears to work very well I have worked 24
countries on 5 continents ( still need Antarctica and Asia...tough on
any band from FL) in just 4 SUMMER months and I am sure that total will
climb quickly once the winter season starts. For the FT8 doom and
gloomers half of these were on CW....8^)
Happy to share details of the 80 and 40 M antennas off list, not
relevant to the topband list !
Dave
NR1Dx
manuals@artekmanuals.com
On 8/25/2019 1:33 AM, K4SAV wrote:
Dave
Just a clarification. I didn't want your actual data. All I wanted
was the length of the wires and the frequency.
Jerry
On 8/24/2019 9:30 PM, K4SAV wrote:
Hey Dave
I'm interested in your data. How long were the radials and what
frequency were you using for the measurements.
I suspect that NEC2 may be close enough to be generally useful
(accuracy is questionable) for a BOG up to 250 ft on 160. My
measurements (several of them) say that NEC isn't close for a 350 ft
BOG. Usually my BOGs are 1 to 2 inches above the dirt because they
sit on dead grass.
I seriously doubt that NEC4 will be accurate for a 350 ft BOG
either. I have seen a 450 ft BOG pattern generated by NEC4 and I can
duplicate it with NEC2, (with only minor insignificant squiggle
differences) and I know that NEC2 is wrong.
I suspect that as frequency decreases or the wire becomes shorter,
NEC answers will improve.
A data point from someone else would be nice to know.
Jerry, K4SAV
On 8/24/2019 7:53 PM, Artek Manuals wrote:
Chuck et all
It is well documented that the the NEC-2 based programs leave
something to be desired� with wires on or very near the ground, This
includes most of the EZENEC� family and MMANA-G� Purportedly NEC-4 (
there is a Ezenec version which runs with NEC 4 engine ... not a
cheap date) does deal with the near earth problem .
How close is "Close" is a matter of conjecture. A friend of mine and
I have been working on building and modeling vertical antennas (
Verticals, Inv-L and T's) for 160/80/40 with ELEVATED NON-RESONANT
radials at 3' and 6' (google "K5IU Elevated Radials") . The good
news is at 3' and above both NEC 2 and NEC 4 models agree within 5%
or better.� We have not done any comparisons below 3'
Dave
NR1DX
On 8/24/2019 1:41 PM, Chuck Dietz wrote:
I seem to remember someone saying the modelling programs are
unreliable
when a wire is close to the ground. Also, there is really no way to
model
the properties of "ground." It can vary in just a few feet and the
moisture
content varies from day to day. I think this is a "try it" kind of
antenna.
Read other's reported results.
Chuck W5PR
--
Dave
Manuals@ArtekManuals.com
www.ArtekManuals.com
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