Howdy -
Here's some info we're having trouble getting posted so I'll try it here.
My apologies if it doesn't come thru in a reasonable fashion. If so, this is
only a test - hi. There's some good info so it might be worth wading
thru. Cheers,Steve K7LXC PS - This is one vote for groups.io if anyone is
keeping score. > There was a similar thread going around on the Topband
reflector last week which set me to wondering why some folks have good success
with certain antenna configurations while others are very disappointed with the
same configurationAll this discussion about the various radial systems got me
to wondering again last night tonight so I ran a series of comparative models.I
used NEC-4 (EZNEC Pro-4 / V6.0) which supposedly models things better near or
on ground (than NEC-2 ) Now .... over the years my actual vs modeled
performance is a been bit checkered especially with low band verticals on 160
and 80. I do not pretend that this is the final word on any of
this.Definitions.1) 160M Inverted L , 60 feet at the top and a 72' horizontal
flat top.2) FCP "folded counter poise ground plane" per what I could find in
the history 33' on side 166' total length. 8' above ground3) Elevated radials;
four 132' radial at right angle and 45 degrees to the plane of the Inv-L 8'
above ground4) On Ground radials; forty-eight radials on the ground , 100'
long5)Poor soil (.001m/s), Average soil (.005 m/s), very very good soil
(.01m/s). When doing the models changes in the dielectric constant had very
little effect so that was held constant at 126) "Gain" comparisons are all done
at a 15 degree take off angleComparisons and some possible conclusions:1) Best
Case/ Worst case comparison: The on ground radial when modeled on average and
very good soil is 6 to 9 dB better than the FCP over very poor soil2) When
comparing the FCP directly to on ground radials for the SAME ground type, the
on ground system is typically 4.5-5 dB better than FCP regardless of ground
type3) The On ground system on VERY POOR SOIL is only 1 db better than the FCP
on Average soil. This one was a bit more of a surprise (intuitively) but also
explains why some of the confusion when comparing performance from station to
station.4) When comparing the 1/4 wave elevated radials directly to on ground
radials for the SAME ground type the. The on ground radials were 1 to 1.5db
better than the elevated radials.5) Those of you who have done extensive
modeling know that depending on the length of the horizontal section in the
inverted L that there is some signal degradation ( pattern distortion) with the
"lowest" gain in the direction the L points. and that the longer the horizontal
section the greater the degradation in that direction. The better the soil type
however the less pattern distortion for the same geometry6) Ground conductivity
is BIG factor and we are talking ground in the far field no just under the
antenna7) Putting your elevated radials with one of them directly under the
horizontal L results in more pattern distortion probably true of FCP too but I
didn't model that8) If a FCP is all you have room for..then go for it. Better
than a single ground rod for sure. Sorta like that saw about the lottery " Your
chances of winning are not that great, but they are a whole lot better than not
buying a ticket at all"Disclaimer and related topics:1) This is what the NEC 4
models showed, take that with a grain of salt. According to some articles I
have read in the last two years, the implication of those that those of us in
heavily wooded settings should take down our 160M wire and concentrate on 10m.
I have worked 156 countries on 160m in the last 2.5 years from a heavily wooded
location with a modest 60' high wire T with four elevated radials over very
poor soil (.0012 on average) here in central Florida where half the time we sit
and listen to guys in New England work EU like they were locals ( which to a
greater extent they are). Probably would be closer to 200 worked if it weren't
for so few expeditions due to C-192) The above analysis was done at a take off
angle of 15degrees for the vertical portion of the signal. My experience is
that the horizontal portion of the Inverted L's of modest proportions doesn't
provide much in the way of radiation not even stateside anyway.3)If your really
interested in your native ground conditions google N6LF, Rudy's work on "OWL
probes"4)A couple of side trips related to elevated radial.Read N6LF's work on
elevated radials VERY CLOSELY before jumping to conclusions: For reasonable
radial lengths (.2 to .4 wavelengths ) more than 4 elevated radials doesn't buy
you much if anything. More radials can help with more even distribution of
radial currents which is often more about pattern distortion than anything
else. If you really concerned about pattern distortion go to a "T" rather than
an inverted L for starters or non resonant radials (see the last
paragraph)Elevating the radials from 8' to 20' buys you a whopping .2db
improvement ( hardly worth the effort IMO)Find a copy of K5IU (sk) article on
non-resonant radials if you're really interested/concerned about the uniformity
of radial currents with fewer (4 or less) in elevated radials. I use non
resonant radials on both 80 and 160 (90' long) and the radial current varies
less than 2% radial to radial. I have a copy of the paper somewhere ..contact
me off list if you have really searched and can't find it
...manuals@artekmanuals.comDaveNR1DX
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