On 01/10/10 03:51, Jim Lux wrote:

Thanks Jim.


I would think that the buried radials are more convenient (broad band,
etc.)

Yes, I understand that there are advantages to buried radials, but I
don't understand the preponderance of cases where I see 120 radials
pinned on the top of infertile dirt. They still present a trip hazard,
and less money spent on just a few elevated radials may perform just as
well.


Look at the performance of your ankle biting radials when the dimensions
are changed slightly.. For instance, if you shorten them by 5%, does it
make a big difference? For the buried radials, the length is very, very
non critical.

Yes, of course the feedpoint impedance is more sensitive to change in
length or conversely change in frequency.


Something else to look at is the sensitivity of "efficiency" (and your
definition of radiated power in the hemisphere/power into antenna is
fine) to soil properties.. if the soil conductivity or epsilon changes
(as it will with changing water content) does the efficiency change
rapidly?

Yes, efficiency is sensitive to soil parameters... for both types, but
not very sensitive.

Because of the impedance change mentioned above, the impedance
transformation needs adjustment for wide range frequency operation. Not
such an issue in the intended application, the DX window on 80m here is
just 50kHz.



Also, what about the loss in any matching components needed (e.g. if you
had a real efficient narrow band antenna, then operating off nominal
means you'll need a different matching network, and the loss in it might
be worth considering)

Matching network loss was not included in my analysis because both
quarter wave options present fairly similar load impedances that need
transformation to 50 ohms. The shortened verticle is slightly lower R
(23 vs 38 IIRC), and slightly more loss can be expected, but it is
practical to match with a shunt coil of copper tube and matching loss
should be real low in the system context, and in comparison of elevated
vs buried radials.

If I haven't got something quite wrong in the modelling, it would seem
worthwhile to prototype the shortened version with a view to extending
the system to a four-square if suitable.

I have still to read Rudy's papers... I am away from home (less
bandwidth) and I will download them later today when I get home. I
suppose that the proposed design challenges the norm of a very large
number of buried radials. In our case, part of the property is quite
rocky, and a configuration with just a few elevated radials offers
deployment opportunities that aren't suited to buried radials.

So, my original question is no so much suggesting everyone else got it
wrong, but why don't I seem more people doing it this way. Could I be
forgive in thinking that the popular, nearly universal, way is to uplift
the BL&E research at MF and apply it to 80m?

Owen

On Sep 30, 3:13*pm, Owen wrote:

Could I be forgive(n) in thinking that the popular, nearly universal, way
is to uplift the BL&E research at MF and apply it to 80m?

The BL&E experiments were conducted using 3 MHz signals, so their
applicability to the 80m band is not a large uplift.

On 01/10/10 06:39, Richard Fry wrote:
On Sep 30, 3:13 pm, wrote:

Could I be forgive(n) in thinking that the popular, nearly universal, way
is to uplift the BL&E research at MF and apply it to 80m?

The BL&E experiments were conducted using 3 MHz signals, so their
applicability to the 80m band is not a large uplift.

I stand corrected. I have read the paper many times, and my recollection
was that it was below 2MHz. Must be time to read it again!

Owen

Owen wrote:
On 01/10/10 03:51, Jim Lux wrote:

Thanks Jim.


I would think that the buried radials are more convenient (broad band,
etc.)

Yes, I understand that there are advantages to buried radials, but I
don't understand the preponderance of cases where I see 120 radials
pinned on the top of infertile dirt. They still present a trip hazard,
and less money spent on just a few elevated radials may perform just as
well.

never underestimate the power of tradition. It was written by BL&E that
120 radials work, and the FCC accepts that for broadcast, so by golly,
that's what we do. Why 120? it was at the point of diminishing returns
or practicality back when the study was done (e.g. there was no
detectable change from going to more)

As for laying on ground.. I think that's more the laying on grass, and
eventually, the wire sinks into the grass/turf.

There's also the whole "the radials must be resonant" misconception..



Look at the performance of your ankle biting radials when the dimensions
are changed slightly.. For instance, if you shorten them by 5%, does it
make a big difference? For the buried radials, the length is very, very
non critical.

Yes, of course the feedpoint impedance is more sensitive to change in
length or conversely change in frequency.

While for a buried radial system (probably because of the losses) it's
going to be less frequency sensitive.




Something else to look at is the sensitivity of "efficiency" (and your
definition of radiated power in the hemisphere/power into antenna is
fine) to soil properties.. if the soil conductivity or epsilon changes
(as it will with changing water content) does the efficiency change
rapidly?

Yes, efficiency is sensitive to soil parameters... for both types, but
not very sensitive.

Maybe less sensitive for the buried radials? Or, it was "good enough"
for BL&E, so being so written, so shall it be done.


Because of the impedance change mentioned above, the impedance
transformation needs adjustment for wide range frequency operation. Not
such an issue in the intended application, the DX window on 80m here is
just 50kHz.




If I haven't got something quite wrong in the modelling, it would seem
worthwhile to prototype the shortened version with a view to extending
the system to a four-square if suitable.

The shortened version will, of course, aggravate the tuning sensitivity.





I have still to read Rudy's papers... I am away from home (less
bandwidth) and I will download them later today when I get home. I
suppose that the proposed design challenges the norm of a very large
number of buried radials. In our case, part of the property is quite
rocky, and a configuration with just a few elevated radials offers
deployment opportunities that aren't suited to buried radials.

So, my original question is no so much suggesting everyone else got it
wrong, but why don't I seem more people doing it this way. Could I be
forgive in thinking that the popular, nearly universal, way is to uplift
the BL&E research at MF and apply it to 80m?

Tradition is a powerful force. Look how many years it took for someone
(e.g. Rudy) to put the substantial work into doing a real quantitative
experiment. For most hams, they're only going to do something once, and
if works ok, that's how it stays. Almost none are going to do a well
controlled A/B study, especially if there's a (not necessarily valid)
tradition that says A works better (where better is ill defined and
probably a combination of radiation efficiency and installation convenience)

Until recently, modeling tools available to most amateurs were not
suitable for making the call, although there have been some people who
did models and published it, but, in the face of decades of "lay down
120 radials" it was a tough sell.

The other thing is whether the difference is big enough to "make a
difference" in observed system performance. For a lot of operators, a 1
dB change in performance might not be noticeable. If you're in a
"either propagation is there, or it isn't" situation the difference
between good and bad is 10s of dB. There are relatively few people who
work at 0dB SNR (where tenths count) on a regular and continuing basis,
and they're not necessarily the ones who are interested in doing
experiments on antennas on the scale needed.






Owen

On Thu, 30 Sep 2010 14:44:53 -0700, Jim Lux
wrote:

It was written by BL&E that
120 radials work,

2, 15, 30, 60, and 113.

No discussion whatever of 120.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Thu, 30 Sep 2010 14:44:53 -0700, Jim Lux
wrote:

It was written by BL&E that
120 radials work,

2, 15, 30, 60, and 113.

No discussion whatever of 120.


I stand corrected.. thanks..
So they extrapolated to 120 as a "nice round number" for the future
purposes of the FCC.

On Oct 1, 4:00*pm, Jim Lux wrote:
Richard Clark wrote:
On Thu, 30 Sep 2010 14:44:53 -0700, Jim Lux
wrote:

It was written by BL&E that
120 radials work,

2, 15, 30, 60, and 113.

No discussion whatever of 120.

I stand corrected.. thanks..
So they extrapolated to 120 as a "nice round number" for the future
purposes of the FCC.

The only reason the FCC used 120, is overkill for the
stations to be able to avoid a costly survey.
If they didn't use 120, they had to do tests to prove
that the system was efficient enough. So most used
120 to avoid all that.
For most cases, 120 is almost twice overkill..
For ham use 60 is usually plenty to get well into
the near optimum range. Any more than that is
a small increase, and usually not worth the cost
of the wire.
Since Owen posted this question, I did a lot more
checking around, and I had already seen the MW BC
examples.
Seems I'm not the only one that doubts that a small
number of barely elevated radials will give a large
increase over ones on the ground.
One that is in my camp is... Yuri will love this..
W8JI.. Tom seems to agree with my stance from
what I can tell. He has done tests in this regard
and his results did not show much of an increase
over the ground installed radials.
In fact, he gave one example where they changed a
MW station from four elevated radials to the usual
buried radials.. I assume 120 of them..
They then had to explain to the FCC why the buried
radials suddenly gave 5 db+ gain over the supposedly
"near perfect" elevated set.. :/
He also did tests on 80m comparing this same thing.
The results did not pan out and pretty much were in
the same ballpark as the results I saw when I tried it.
IE: the elevated radials are slightly better than the same
number on the ground, but only by a small amount.
His tests showed that the usual buried radials using
60 or more greatly outperformed the three or four
elevated radials. By 5 db+..
Myself, I think for four elevated radials to equal even
sixteen on the ground would require them to be almost
1/8 wave off the ground.
So it seems I'm not alone in my doubt of this
supposed free lunch program. W8JI seems to be
in my doubtful camp. A few others too actually.

Jim Lux wrote in news:i85i4p$enq$1
@news.jpl.nasa.gov:

Richard Clark wrote:
On Thu, 30 Sep 2010 14:44:53 -0700, Jim Lux
wrote:

It was written by BL&E that
120 radials work,

2, 15, 30, 60, and 113.

No discussion whatever of 120.

There might not have been much "discussion" though it is mentioned, but
the summary does contain the following:

"It is also found that a ground system consisting of 120 buried radial
wires, each on half wave long, is desirable".



I stand corrected.. thanks..
So they extrapolated to 120 as a "nice round number" for the future
purposes of the FCC.

It does appear that if someone blessed the number 120, it was probably
BL&E who did it, even if they were talking about half wave radials.

Owen

On Thu, 30 Sep 2010 14:44:53 -0700, Jim Lux
wrote:

For a lot of operators, a 1
dB change in performance might not be noticeable.

That 1dB is at the periphery of a radius where surface area
(customers) mounts up by the square.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Thu, 30 Sep 2010 14:44:53 -0700, Jim Lux
wrote:

For a lot of operators, a 1
dB change in performance might not be noticeable.

That 1dB is at the periphery of a radius where surface area
(customers) mounts up by the square.


For broadcasters, sure. But the discussion is in reference to the
potential performance difference for ham use, and I would think that
there is more than 1 dB variation in the "other end" of the link. The
hard core DXer or QRPer digging the signal out of the noise will care,
but that's a small fraction of the overall ham population.