Hi Hasan,

I have not forgotten your model. I am very interested in verifying
the findings of Reg's program, so will get around to it. I will be
very busy this weekend, so may not have a chance until the
beginning of next week. I have been investigating some of
the limitations of NEC, and 1 mm below ground is one of
them (Not necessarily because of the depth, but segmentation
issues). I will try and get as close to your model parameters
as possible. This afternoon I was sidetracked by a challenge
from Reg, and spent about 90 minutes running a model
similar to yours. Interestingly enough there appears to be
a very large discrepancy between the programs.
NEC 4.1 indicated only 30.5 % efficiency.
(See later thread).

Frank


"hasan schiers" wrote in message
...
Hi Frank,

I think the general question became "can one use this Rrad value in
calculating efficiency". I'm waiting for Tom's response to my last
posting.

On the other issue, radial length vs. usefulness, (I tried a diect mail
to you and it didn't make it cuz I forgot to take out the nospam part),

here is what I want to know from NEC-4:

Radial wire is #14 THHN inslulated wire. I approximated it at 2mm. The
antenna wire is 4 mm. For these purposes, you can probably forget that the
wire is insulated.

Now...looking at radial length (assuming 26 radials), and given the
constants I previously provided, how long does a radial in this
configuration have to be, before it is no longer valuable to increase its
length. Tom says he measured significant current in a radial well beyond
where Reg's program says the current had diminished to insignifcant
levels.

I would be MOST interested if you can confirm Tom's measurements. If NEC-4
says there is substantial radial current where Reg's program says there
isn't, then that is an important contradiction, putting Reg's model into
question. I'm giving more credibility to NEC-4 (properly used) than I am
to Reg's own design. If, however, we have two sources (one measurement
based: Tom, one model based: NEC-4), that say Reg's theory that radials
quickly approach maximum effectiveness over a MUCH shorter run than has
been previously understood (in moderate to very good soils), that
contradict Reg's algorithim.

Having only looked at conclusions from BL&E, I can't say what their
measurements indicated in terms of radial current vs. length. Ian has
suggested that they did measure the radial current vs length and they
concur with Tom. So, if BL&E and Tom (both empirical), as well as NEC-4
(model based), all say that important levels of current are present in
radials well beyond where Reg's program predicts, then there's only one
conclusion left. (Unless I'm missing something).

This, to me, is much more interesting stuff than a month long peeing
contest over precipitation static.(which may be rearing its ugly head yet
again in the "double bazooka" thread. God help us!

73, and thanks for your comments and efforts to help me understand what is
going on.

...hasan, N0AN
"Frank's" wrote in message
news:ZO5wg.115459$A8.61548@clgrps12...
I understand there are measurement issues (and certainly assumption
issues
for Rrad). Isn't is fairly certain that increasing the number of radials
(of proper length) until the feedpoint R (at resonance, at the antenna)
no longer drops, is a reasonable approximation of "high efficiency"? The
only issue I see, is determining the target Rrad to compare it to when
trying to "estimate" efficiency.

Are you saying (for example), that the feedpoint R of a 1/4 w vertical
against perfect ground cannot be reliably estimated at 37 ohms? If it
can, then isn't 37/R a measure of efficiency?

Again, I'm thinking of the efficiency of the ground system... I have no
way to look at field strength.

Is it really possible to reduce ground losses to the absolute minimum
and not have a corresponding increase in field strength?

This is starting to turn into "black magic" for me. I can understand
questioning a particular "number" for efficiency based on the simplistic
Rrad/R formula. If the implications go further...indicating there is no
meaning to Rrad/R, then I'm lost.

Perhaps the issue is that it's known how to maximize efficiency, it's
just completely unknown what that efficiency really is, and there is no
simple way to measure it. If that's what your saying, then I understand.

That position does seem to muddy up the "how many radials and of what
length" efficiency info presented in ON4UN's book and referenced in
other texts. They all seem to acccept some sort of accuracy for the
Rrad/R formula with 1/4 w verticals. If I understand you correctly, the
formula is rejected outright as hopelessly simplistic, and of no
particular value.

Do I have it now? If so, I'll refrain from using it in the future.

I had always assumed that a NEC model of a perfectly conducting
monopole above a perfect ground would provide the radiation
resistance. For example, considering your antenna of 18.3 m
at 3.62 MHz, the input impedance is 27.5 - j 64.7. The radiation
resistance would therefore be 27.5 ohms. This appears to be
fairly close to your estimate of 25.4 ohms.

Frank