surprising! info about vertical antennas and poor soil

[loosecannon]

i found this very eye opening, but would like to hear some other opinions.

if i am not mistaken, according to this article; the best DX performance with a vertical antenna on the upper HF bands would be from a 5/8 wavelength radiator with 90* radials, up over 25 feet in the air, over very poor soil.
go figure.

what do you think?
http://www.cebik.com/gp/58-3.html
loosecannon

 

[Master Chief]

The best DX is the signal that gets through, whether it starts out vertical or horizontal.

The best vertical signal comes from a 5/8 wave antenna.

As I've said over and over, people figured this out many many years ago. Only recently have computer modeling been available to verify what people have experienced for years.

While computer modeling is not perfect, the experts use these models as a beginning and back it up with real life testing.

FYI, the broadcasters at the bottom of the rf spectrum are also using verticals with ground planes. I know, I've worked on them.

 

[loosecannon]

the eye opening part for me was that the lowest angle of radiation was the strongest lobe over very poor soil conditions.
i live in the desert, and lots of the locals here water their antenna bases in hopes of a better RF ground.
some even add salt to the water.

nice to find out that these efforts are in vane if DX is the goal.

im gonna catch hell for telling them about what i read.LOL
loosecannon

 

[Master Chief]

Those 90 degree elements simulate a ground, and the lowest angle of radiation gives you the best DX. The soil has little to do with the performance of a GROUND PLANE antenna's radiation pattern. Vertical and horizontal dipoles are a different issue.

Did you know that four ground radials are better than three, but there is almost no advantage using more than four.....in the upper part of the HF band.

 

[W5LZ]

loosecannon,
"Eye opening"? Good. The thing is, don't draw too many conclusions from Cibek's testing without more testing of those conclusions. I'm not saying Cibek isn't correct in what he described! Just that it isn't something you need to worry about 'writing in 'stone' because it's something new. It isn't new, it's been around for a very long time. (It does show some of the benefits from at least being a little familiar with the antenna modeling programs.)
You might wanna take another look at a few of those results, by the way. The angle of the radials used for ground are not exactly 'written in stone'. The AOD ('angle of the dangle', or declination if you wanna get technical) on 10 meters (45 degrees) is slightly 'better' than the one for 20 meters (90 degrees). Not something that's all that important unless you use that AOD for input impedance adjustments.
- 'Doc


And 'M.C.'s right, that groundplane is just something that's taking the place of 'dirt'.

Which brings up some interesting ideas. If you could make whatever's immediately under that vertical element 'dirty' enough, you wouldn't need the radials!
Or...
If you motorized the radials so that you could adjust their 'dangle', it should make the take off angle adjustable!
Or...
Use a 'screwdriver' type vertical element and you could change frequency, take off angle, etc.!

Time for my meds...

 

[Master Chief]

Use a 'screwdriver' type vertical element and you could change frequency, take off angle, etc.!

Now you did it! It will only be seconds before KingCobra pops in here talking about the BiggIR!!! 8) 8)

 

[Marconi]

'Doc says:

If you motorized the radials so that you could adjust their 'dangle', it should make the take off angle adjustable!

I have heard this remark on these forums and in some advertising, that the angle of the GP radials has such an affect, but I have never read a thing substaintating that this angle has anything to do with the angle of radiation. I have read where lowering the angle of the radials as the affect of raising the feed point impedance a bit, and I can even test that to be true. But, have heard nothing about the TO angle getting either better or worse as in adjustable.

What I have found in doing this is, maybe the feed point impedance is improved towards 50 ohms a bit as I lower them from the horizontal, but I suspect that all that I am really doing is to increase losses a bit while showing a better match. I say this because, in such tests, the field strength always seems to diminish a bit.

Can someone elaborate a bit, or provide a published, so-called professional source where this is discussed and how is this determined in testing?

 

[freecell]

"The soil has little to do with the performance of a GROUND PLANE antenna's radiation pattern."

all of the antennas tested were ground plane antennas and the "lower lobes dominate over the poorest soils." the same effect with end fed half wave verticals is even more pronounced. the angle of the radials only add or detract from the feedpoint impedance and contribute nothing to the angle of radiation one way or the other although with the 90 degree radials the amount of energy wasted in the upper angle lobes is somewhat lessened. better read it again. the quality of the soil in terms of conductivity (or lack thereof) has everything to do with the radiation pattern of a ground plane antenna, that was the point of the entire article.

no surprises there. what i'm really surprised about is that cebik doesn't seem to understand why.

"maybe the feed point impedance is improved towards 50 ohms a bit as I lower them from the horizontal, but I suspect that all that I am really doing is to increase losses a bit while showing a better match."

the slight drop in your field strength readings as you droop the radials to achieve a closer match to the feedline is caused by increased energy distribution in the higher angle lobes.

 

[Marconi]

Well freecell, while improving the match with lowering the radials, I seemed to be loosing effectivness a bit at the same time. Do you think maybe that is why I was seeing less field strength when lowering the GP radials from the horizontal in my test?

 

[freecell]

yes, see appended post above, last two paragraphs.

 

[Marconi]

So the pattern is affected by a change in the angle of the radials and maybe 'Doc is right to a point, with a bad choice of words.

 

[freecell]

yes, just not the way everyone thinks that it is. just because the radials are lowered doesn't mean the lobe angle necessarily follows suit. sweeping the radials upward in the case of the sigma4 did more to lower the AOR in that particular design than lowering them in the case of a conventional 1/4 or 5/8 monopole.

 

[bob85]

BINGO

 

[W5LZ]

Marconi,
When that field strength decreased, where and how were you doing the measuring? And since it would seem that if improving the impedance match would make the antenna more effective, radiate more because more could reach the antenna, where did that 'increase' in signal strength go? It had to go somewhere didn't it?


'M.C.',
Sorry, wasn't thinking. Then again, do those things use radials? Beats me, they all have a 'quality' that make me very $hy of them.

 

[Marconi]

Well 'Doc, I just moved the meter's antenna around about the the 102" whip mounted with a mobile L-bracket on a 12' high mast that I was testing until I got a 1/2 scale reading. The meter's antenna was probably 20' away.

As I added a GP element, I read and recorded the analyzer readings at 27.200 using a short jumper. Then I fed the antenna with 8 watts to get a field strength reading and recorded that.

I just repeated this one element a time adding a total of 3 elements at 90 degrees and then 3 elements at 45 degrees.

Later I also combined both 90 degree and the 45 degree elements, one after another, and noted those results as well.