[TowerTalk] FCP vs On ground.txt

[Steve Maki]

Here, maybe this will be easier to read...

-Steve K8LX

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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.

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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 configuration.

All 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 ground.

3) Elevated radials; four 132' radial at right angle and 45 degrees to 
the plane of the Inv-L 8' above ground

4) On Ground radials; forty-eight radials on the ground , 100' long

5) 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 12.

6) "Gain" comparisons are all done at a 15 degree take off angle.

Comparisons 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 soil.

2) 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 type.

3) 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 geometry.

6) Ground conductivity is BIG factor and we are talking ground in the 
far field no just under the antenna.

7) 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 that.

8) 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 at artekmanuals.comDaveNR1DX
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