Not enough coffee earlier a better description of the radials: three
90ft radials radials 7'ft high spaced in 120 degree increments (0,
120and 240 degrees)
Another interesting side notes discovered while doing the modeling
1) A three radial version in a 180 degree half circle (0, 90 and 180) or
what I like to call the "up against the fence", resulted in very much
the same modeled impedance and only slight pattern distortion ( less
than 1db) , Predicted radiated field strength by adding the forth
radial at 270 degrees only resulted in an increase in signal in that
direction a few tenths of a dB
2) Inverted L's pattern distortion can be non trivial depending on the
length of the top section. The signal decreases in the direction the top
section "points". In the past I had a preference for having very long
top sections ( Total length: vertical + horizontal on the order of
150') so as to increase the real portion of feed point impedance to
50ohms and then tune out the increased reactive portion with a series
cap. Depending on how long the top section is signals in the direction
of the pointing top of the L can be down by as much as 3 to 6dB !!. At
the new QTH the best tree supports resulted in a 6db pattern decrease
directly pointed a Europe 8^(... Which is why I ended up with a "T"
instead of an "L".)
Dave
NR1DX
On 8/25/2019 8:25 AM, Artek Manuals wrote:
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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