On Fri, 26 Mar 2004 17:31:28 -0600, Cecil Moore
wrote:

Does anyone else
(besides Tom) have rules-of-thumb that achieve 0.0000000003 accuracy?
E = I · R

Tdonaly wrote:
... so you don't have to rely on rules of thumb that get you
into arguments like this.

Nice try at obfuscation, Tom, but I have previously identified my postings
as only rules of thumb. You attempted to hold my rules of thumb to 0.00000000003
accuracy. Doesn't that make you feel the least bit silly? That's stretching
things pretty far to try to prove that anyone who believes in reflected waves
is crazy. Have you figured out how standing waves can occur without the existence
of reflected waves yet? I've been holding my breath for that proof you promised.

If my rules of thumb are within 20% accuracy, I consider that pretty good.

And here I repeat my rules of thumb. The ratio of the resonant feedpoint impedance
to the antiresonant impedance of a dipole is about 100 to 1. The maximum reactance
point between those two frequencies is about Rmax/2+jRmax/2. If you can't prove
that rule of thumb is less than 20% accurate, you have no argument.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote in message ...


Yes, that's true. Now try it with a thin wire on HF. I believe what
you will find is that at the maximum reactance point, the resistance
is approximately half of the one-wavelength (anti)resonant value.
At the maximum reactance point, the resistance and reactance are
approximately equal. Since the maximum reactance value lies between
two points of pure resistance, doesn't it make sense that it might
be approximately where the resistance is half of the maximum value
of resistance?

That's pretty approximate, Cecil. From EZNec for a 10 meter 1mm diam
wire, I got about 2570+j2277 at 27.00MHz. The resistive and reactive
parts differ by over ten percent.

Be that as it may, if you evaluate the SWR tangency thing for a high
reference impedance, you will see that it's a GROSS error, not a tiny
one. You said it wouldn't change with changes in reference impedance,
but it does, and in a major way. Yes, the error is tiny for your
assumed 2500+j2500 evaluated against Z0 of 50 ohms, but the error is
huge if you evaluate against Z0 of, say, 2000 ohms.

And we're still back to not having said anything about _why_ the
reactance peaks at the frequency it does relative to the half- and
full-wave resonances.

Cheers,
Tom

Tom Bruhns wrote:
That's pretty approximate, Cecil. From EZNec for a 10 meter 1mm diam
wire, I got about 2570+j2277 at 27.00MHz. The resistive and reactive
parts differ by over ten percent.

For an approximation that I carry around in my head, 20% accuracy
is good enough for me.

Be that as it may, if you evaluate the SWR tangency thing for a high
reference impedance, you will see that it's a GROSS error, not a tiny
one. You said it wouldn't change with changes in reference impedance,
but it does, and in a major way.

Actually, what I said is that the maximum reactance point on an SWR
circle doesn't depend upon Z0 and proved it with equations.
Xmax/Z01 = X1 normalized for Z01. Xmax/Z02 = X2 normalized for Z02.
X1 and X2 are different but Xmax is the same value no matter what the Z0.

Yes, the error is tiny for your
assumed 2500+j2500 evaluated against Z0 of 50 ohms, but the error is
huge if you evaluate against Z0 of, say, 2000 ohms.

That wouldn't be a logical thing to do. The highest Z0 commonly available
to hams is around 600 ohms. The higher the SWR, the more accurate is this
approximation. Conversely, the lower the SWR the more inaccurate is
this approximation. Since I encounter SWR's in the general range of
10-25, it works pretty well for me.

And we're still back to not having said anything about _why_ the
reactance peaks at the frequency it does relative to the half- and
full-wave resonances.

_Why_ am I sitting at my computer right now? Because I'm not somewhere
else? :-) The reactance seems to peak about 85% of the way between the
1/2WL frequency and the one-wavelength frequency. QED folks seem to
be satisfied with just an equation which doesn't ask or answer, _why?_.
They say, "That's just the way it is."
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil wrote,

Tdonaly wrote:
... so you don't have to rely on rules of thumb that get you
into arguments like this.

Nice try at obfuscation, Tom, but I have previously identified my postings
as only rules of thumb. You attempted to hold my rules of thumb to
0.00000000003
accuracy. Doesn't that make you feel the least bit silly? That's stretching
things pretty far to try to prove that anyone who believes in reflected waves
is crazy. Have you figured out how standing waves can occur without the
existence
of reflected waves yet? I've been holding my breath for that proof you
promised.


I think you've got your Toms mixed up, Cecil. I haven't said anything about
0.000...003 accuracy. The rest of your post you'll have to take up with
Tom Bruhns, although I think your comments on whether or not I "believe
in" reflected waves is unmitigated balderdash.
I'm going to quit posting on this, Cecil. Your replies are
irrational and it's clear that the strain of dealing with two Toms at once
is too hard on your head.
73,
Tom Donaly, KA6RUH

Tdonaly wrote:
... I think your comments on whether or not I "believe
in" reflected waves is unmitigated balderdash.

Have you changed your mind from last time?
--
73, Cecil http://www.qsl.net/w5dxp



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Tdonaly wrote:
I think you've got your Toms mixed up, Cecil. I haven't said anything about
0.000...003 accuracy.

I didn't say you did, Tom. That "you" I used was plural. Maybe
I should have said "y'all"?
--
73, Cecil http://www.qsl.net/w5dxp



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On Sat, 27 Mar 2004 12:10:36 -0600, Cecil Moore
wrote:

Tdonaly wrote:
I think you've got your Toms mixed up, Cecil. I haven't said anything about
0.000...003 accuracy.

I didn't say you did, Tom. That "you" I used was plural. Maybe
I should have said "y'all"?

On Fri, 26 Mar 2004 19:14:03 -0600, Cecil Moore
wrote:

Nice try at obfuscation,

The plural "you" is inclusive, which is still a miss-attribution.
This compounds the error.

Cecil Moore wrote in message ...

For an approximation that I carry around in my head, 20% accuracy
is good enough for me.

Ah, we started out with exact geometric relationships that defined
precise points, and now we're down to 20% accuracy being OK. I got
it. Thanks.

Cheers,
Tom

Richard Clark wrote:
The plural "you" is inclusive, which is still a miss-attribution.
This compounds the error.

Not necessarily, Richard. I can say to an Oklahoma State basketball
player, "You won your last game", even though he sat on the bench the
entire game and didn't score any points. All members of the
same team are guilty by association if not by actions.
--
73, Cecil http://www.qsl.net/w5dxp



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