Stefan Wolfe wrote:
. . .
A third antenna, not discussed here, would be a real 1/4 W monopole that is
truely connected to earth ground and uses no radial conductive elements.
Here, the monopole functions as a dipole but 1/2 of the radiation pattern
exists as a mathematical image reflecting against true ground (not a good
conductor of electrons like radials, merely a zero voltage reference point).
Although the mathematical image seems to only exist in theory, the observed
physical effects of RF transmission follows the rules of energy conservation
and the antenna transmits real RF that can be measured as if it were a true
vertical dipole antenna. Now you have seen the real evidence that the host
is the true body of Jesus Christ! ...the radials were simply a false
religion. The phantom/true earth side of the dipole in the 1/4W monopole
ground plane similuates a real metal conductor, mathematically and
physically. The only advantage here is that the grounded monopole is 1/2 the
height of the full metal conductor dipole.

Unfortunately the Earth is largely covered with dirt. It's unclear to me
how you "truely connect" to it. Radials provide the lowest loss
"connection", but you seem to know of a better way. Please describe it
for us.

Even if you could make a zero-loss connection to ground (and a large
radial field comes close enough for nearly all practical purposes), that
dirt still doesn't provide the "mathematical image" of a perfect ground
plane. The net effect of the ground's finite conductivity is that the
low angle part of the radiation is absorbed in the dirt, heating the
earthworms and resulting in a radiation pattern that doesn't resemble a
free-space dipole (or monopole over a perfect ground) very closely at
all. These effects can be clearly seen with any modern modeling program
including the free EZNEC demo. Example file Vert1.ez uses a
"MININEC-type" ground which does provide a zero resistance "connection"
to ground, something you can approach but not completely accomplish in
practice. Compare the pattern of this model to the same one with a
perfect ground (superimpose the two on the 2D plot so they're drawn to
the same scale) to see how poor an approximation dirt is to a perfect
image plane.

Interestingly, whereas radials simulate (very inefficiently) a true ground
system, a true ground system simulates that which the radial system cannot
achieve very well, but both attempt to acheive the same end. One is ground,
the other is more like a counterpoise or misplaced antenna element for a
balanced antenna.

I don't understand that at all. But as you pointed out a while back, I'm
a ham with an American Extra Class license, so I know I can't be
expected to understand anything very complicated. (Worse yet, I took the
exam 44 years ago, so 9/10 of what I knew then is obsolete, and I've
forgotten the rest.)

Roy Lewallen, W7EL

"Cecil Moore" wrote
The average gain of a 1/4WL vertical monopole
with ground-mounted radials is in the ballpark
of 0 dB in all directions.

It is extremely difficult, if not impossible,
for a vertical monopole to achieve 6 dB gain
in any direction.
____________

Zero or six decibels with respect to what reference, Cecil?

If that reference is an isotropic radiator, then note that a typical
1/4-wave monopole and buried radial ground system used by commercial,
non-directional AM broadcast stations has an h-plane gain of about 5 dBi.
This value has been confirmed by thousands of groundwave field strength
measurements of such systems going back 70+ years. Also note that the gain
of this monopole over a perfect, infinite ground plane would be only 5.15
dBi, so a broadcast radiator is quite good indeed.

And -- a gain of more than 6 dBi is produced by broadcast monopoles whose
height exceeds 1/4-wave sufficiently. For example, the h-plane gain of a
1/2-wave broadcast monopole system is about 6.6 dBi (6.8 dBi over a perfect
ground plane).

RF

Stefan, do you have those religious fantasies often? You know we do
have drugs now, that cure those.... Drugs are preferred over the old
tried and true cure, which involved piles of dry wood, pubertal girls,
and combustion...
Anyway; Hey I enjoyed your discussion... Now back to the task at
hand...

Rick, to improve DX performance on a quarter wave vertical over a
reasonable radial field I have to go to a dipole at 100 feet, or to
one of the high inverted vees, 120 & 150 feet.. While I no longer have
a horizontal antenna below 100 feet for 80, when I did the quarter
wave vertical shone on DX compared to the lower horizontal antennas..
Secondly, 18 radials just will not do it when you care to send the
very best hallmark... An absolute minimum of 30 is needed, and for
long dx 50+ is going to be neeeded... By the time you have the radial
count up to the 50-60 range you have pretty well maxed out any major
improvements until you surpass a 100...

Now, there are those who like elevated radials Christman and those
who hate em Rauch.. I have to say that my personal experiences on
160 is that 10 or 12, 1/4 wave and tuned, elevated radials works - but
they are a pain to keep in the air (in the woods), and tuned, and
working... I worked Heard Island with the elevated array on 160...
My current 160 ground mounted vertical array has well over a hundred
radials of varying lengths and seems to work (G3 from the black RF
hole of Michigan on 100 watts while the amp was warming up two nights
ago, so it plays reasonably well)
Now a dipole or vee at 130 feet is simply not going to work on 160,
period... Oh yeah, you can wow the guys at 700 miles with your NVIS
signal, but you will get trampled in a dx pileup...

So bottom line, even on 80, is that you need to either go to an
elevated array as others suggested, or you need to improve your ground
radial count - at which point the vertical will shine over a low vee
at 1000 + miles...

Roy, similarily in my profession; I know that half of everything they
taught me is wrong, they just won't tell me which half!

cheers

Richard Fry wrote:
"Cecil Moore" wrote
The average gain of a 1/4WL vertical monopole
with ground-mounted radials is in the ballpark
of 0 dB in all directions.

It is extremely difficult, if not impossible,
for a vertical monopole to achieve 6 dB gain
in any direction.

Zero or six decibels with respect to what reference, Cecil?

Sorry, I had a senior moment - should have been dBi.

If that reference is an isotropic radiator, then note that a typical
1/4-wave monopole and buried radial ground system used by commercial,
non-directional AM broadcast stations has an h-plane gain of about 5
dBi. This value has been confirmed by thousands of groundwave field
strength measurements of such systems going back 70+ years. Also note
that the gain of this monopole over a perfect, infinite ground plane
would be only 5.15 dBi, so a broadcast radiator is quite good indeed.

I was speaking of the typical ham radio 1/4WL monopole.
EZNEC's VERT1.EZ is an example of such an antenna with
a maximum gain of about 0 dBi.

The point was that the average 1/4WL amateur monopole
doesn't equal the maximum gain of an average 1/2WL dipole,
much less the gain of a more directional antenna.
--
73, Cecil http://www.w5dxp.com

"Roy Lewallen" wrote
Even if you could make a zero-loss connection to ground (and a large
radial field comes close enough for nearly all practical purposes), that
dirt still doesn't provide the "mathematical image" of a perfect ground
plane.
___________

Expanding on this for S. Wolfe, even if a point connection having zero
resistance to earth potential existed at/near the base of a vertical
monopole, a monopole using that ground reference would be a poor radiator.

This is because the r-f ground currents that need to flow back into the
antenna system first would need to travel through the lossy earth from
distances up to 1/2 wavelength from the monopole, to reach that perfect
ground connection.

The function of the buried radials is to provide a low-resistance path for
those ground currents, which means that they have to be collected as closely
as possible to their sources in the earth (eg, within a disc having a radius
of 1/2-wavelength around the monopole).

A benchmark field study in 1937 by Brown, Lewis and Epstein of RCA showed
that about 120 buried radials each at least 1/4-wave long enable a
groundwave field to be radiated by a monopole that is within a few percent
of that over a perfect ground plane. Ground conductivity at their test site
was no better than 4 mS/m. Their test frequency was 3 MHz.

RF

"Cecil Moore" wrote
I was speaking of the typical ham radio 1/4WL monopole.
EZNEC's VERT1.EZ is an example of such an antenna with
a maximum gain of about 0 dBi.

And NEC shows that such maximum gain occurs at some angle above the
horizontal plane, maybe 20 degrees? NEC also shows zero relative field in
the horizontal plane, and very low values below elevation angles of 10
degrees or so.

But note in the graphic linked below that for broadcast stations using
1/4-wave monopoles, nighttime skywave coverage in the range of 400 to 1,000
miles is provided by radiation in the range of 1 to 20 degrees elevation.
Both theory and practice show that monopole radiation for these conditions
could not be as given in a NEC analysis showing the field at an infinite
distance.

http://i62.photobucket.com/albums/h8...ermanFig55.jpg

The point was that the average 1/4WL amateur monopole
doesn't equal the maximum gain of an average 1/2WL dipole,

It could get very close to it though, with the necessary buried radial
system.

RF

So my conclusion is that even though the vertical might have the low angle
pattern, the losses in the soil do not allow the advantages to be realized.
Phased arrays of similar antennas over lossy soil may show the nice pattern
and f/b but the absolute value of gain expected may not be realized.

My experience in MS (clay soil) comparing a dipole (nearly flat-top) at
about 90 feet to verticals is that the verticals nearly always win for dx.
(this is on 3.5 MHz).

However, I usually put down ~50 1/4-wave radials for the verticals.
I would definitely increase the number over 18.

My qth is also surrounded by a large number of large pines. In fact
the verticals I compare to are wires supported by the trees.
I have no idea how much they affect the signal, but verticals still
outperform dipoles for dx at my qth.

Do you have other metal objects or ground clutter (houses, etc) near to
the vertical? What was the feedpoint impedance of the vertical?

Tor
N4OGW

On Nov 7, 6:24 am, Denny wrote:


Now, there are those who like elevated radials Christman and those
who hate em Rauch..

Dunno..I can't remember W8JI using elevated verticals..
He may be seeing a large number of people that
run elevated, but don't use enough radials for the
height in wavelength. Most don't, and then wonder
why they don't play as planned..
Most 160m elevated verticals are still going to be low
to the ground as far as wavelength.
Sixty feet is only 1/8 wave. To equal a GP at 1/2 wave
requires appx 60 radials. This also equals 120 radials on
the ground. 1/4 wave up requires appx 8-10 or so radials
to equal the same ground loss.
On 160m, many think they can elevate a vertical 20
ft or so, and use maybe 4-8-10 radials to get good
performance.
It just doesn't work that way. At such a low height in WL,
they need almost as many as a ground mount.
On 160m, a ground mount is really more practical as
everything is large. It will be a lot easier to plant
60+ radials on the ground than it will be to raise the
vertical to a decent height. This might apply to 80m
also for most people..
But on 40m, it's not hard to set up a decent GP,
and my 32 ft whip was fully self supporting.


Now a dipole or vee at 130 feet is simply not going to work on 160,
period... Oh yeah, you can wow the guys at 700 miles with your NVIS
signal, but you will get trampled in a dx pileup...

Heck, W8JI ran a 160m dipole at 300+ ft.. The verticals still
won as a transmit antenna to DX. I think he uses 60 radials,
unless he's added more since that time. I forgot what his
vertical is.. A tower of some fairly tall height... It ain't no
typical ????
brand multiband dummy load on a stick... :/
MK

wrote
On 160m, many think they can elevate a vertical 20
ft or so, and use maybe 4-8-10 radials to get good
performance. It just doesn't work that way. At such a
low height in WL, they need almost as many as a ground
mount.
__________

You may be interested in the paper linked below, which reaches
a very different conclusion, verified by field experience.

NEC models of this system in the broadcast band with the radials elevated 20
feet show gains equal to those using a classic broadcast buried radial
ground system. And if this true in the broadcast band, I expect it is true
for 160 meters.

http://www.nottltd.com/ElevatedRadialSystem.pdf

RF

On Nov 7, 2:08 pm, "Richard Fry" wrote:
wrote On 160m, many think they can elevate a vertical 20
ft or so, and use maybe 4-8-10 radials to get good
performance. It just doesn't work that way. At such a
low height in WL, they need almost as many as a ground
mount.

__________

You may be interested in the paper linked below, which reaches
a very different conclusion, verified by field experience.

NEC models of this system in the broadcast band with the radials elevated 20
feet show gains equal to those using a classic broadcast buried radial
ground system. And if this true in the broadcast band, I expect it is true
for 160 meters.

http://www.nottltd.com/ElevatedRadialSystem.pdf

RF

The only problem is I see no direct comparisons to a normal set
of buried radials. Only that they were able to meet the "minimums"
required by the FCC. I would be curious to see how well the 6 radial
setup would compare to a non crippled set of 120 radials.
It's interesting, and I'd already seen it, but I'm not really
convinced
thats it's equal to 120 radials in the ground.
Certainly usable though..
I've seen plenty of tests done by amateurs that pretty much swings
in the other direction. In fact, being my 40m GP was on a
push up mast, I was able to try it with it's four radials, but at
lesser heights. It did not work near as well at 1/8 WL, vs it's
normal 1/4 WL height. And in terms of wavelengths off the ground,
it had an advantage over the 160m scenario.
Also, modeling might show them equal, but that still doesn't really
convince me until I see it happen in the real world.
I've seen a lot of hams have very mediocre results doing pretty much
the same thing on 160 and 80. I remember one in particular that
got fed up and replace it with a set of normal radials on the ground.
Greatly improved his performance.
I guess I'm a firm believer in the loss per number of radials vs WL
I often quote... :/
So far, I've never seen any indication they are off by any great
degree.
BTW, I still prefer the elevated vs ground mount. I'm just not as
optimistic about the number of radials required to equal 120 in the
ground as they are. :/
MK