Richard Harrison wrote:

Richard Clark wrote:
"The Thevenin model only requires an IMPEDANCE."

Yes, but "To secure maximum power output from a generator whose emf and
whose internal impedance are constant, the load must have an impedance
equal to the conjugate of the generator`s internal impedance." (page 43,
"Transmission Lines, Antennas, and Wave Guides", King, Mimno, and Wing)

Anything about dissipationless resistances or negative resistances?
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil, W5DXP wrote:
"Anything about dissipationless resistances or negative resistances (in
"Transmission Lines, Antennas, and Wave Guides")?"

On page 73, the characteristic resistance of free-space is defined as
the sq rt of the permeability of space devided by the dielectric
constant of space. The units are henries/m and farads/m. The solution is
a voltage to current ratio of 376.7 ohms, or 120 pi ohms.

As free-space is a perfect (lossless) medium for radio waves, it is a
dissipationless resistance.

On page 13, the characteristic resistance (Ro) of a transmission line is
given in formula (14.3) as the sq rt of L/C, but this is an
approximation for low-loss lines as there are no perfect lines.

Negative resistance is a gain instead of a loss. The authors of
"Transmission Lines, Antennas, and Wave Guides" were writing for WW-2
officers being trained at Harvard University in radio and radar. The
phone system was then using some "negative resistance repeaters" but
neither these nor "active antennas" were big at that time. You can only
make up the loss in a two-wire phone loop with amplification. Any more
gain and the loop "sings" (breaks into oscillation).

Best regards, Richard Harrison, KB5WZI

On page 73, the characteristic resistance of free-space is defined as
the sq rt of the permeability of space devided by the dielectric
======================

Why must engineere resort to quoting from their worshipped Guru's who are
hardly more likely to be correct than they are themslves.

In all probability the recipient of the advice does't have a copy of the
sacred text. If he did he wouldn't be asking the question anyway. And it
must be extremely rare for anybody to spend weeks attempting to find a copy.
He knows he will have lost interest long before he finds one.

Do engineers these days, in their daily work, depend entirely on the 'gospel
truths' to be found in text books on their extensive book shelves without
much understanding of what its all about? It's a recipe for time-wasting
errors!

Or are they content to obtain money under false pretences?

Sorry about the diversion. I'm in that sort of mood tonight. I'm on Pinot
Noir 2001, red - a product of Romania, bottled before Romania became a EU
member. But it's no worse than the Italian, Spanish, French, or even the
Californian plonk!

Never sampled a 6-shooter, John Wayne, Texan vintage.
----
Reg.

"Reg Edwards" wrote in message
...
On page 73, the characteristic resistance of free-space is defined as
snip-
Sorry about the diversion. I'm in that sort of mood tonight. I'm on Pinot
Noir 2001, red - a product of Romania, bottled before Romania became a EU
member. But it's no worse than the Italian, Spanish, French, or even the
Californian plonk!

Never sampled a 6-shooter, John Wayne, Texan vintage.
----
Reg.


Reg
I shot a big rattlesnake just the other day with a 6-shooter. He was in the
ham shack. Threatened my life.
I used a Smith and Wesson model 19 in blued steel with a 4" barrel. It was
loaded with rat shot.
You're always welcome at my QTH and I'll give you a choice of 6-shooters,
from a .32 S&W to a .44 magnum.
Spirits are consumed only AFTER shooting, however.
Tonight I'm looking forward to a Chateau St Michele merlot with my rare
filet.
73
H.
NQ5H

If rattle-snake meat is fit for human consumption I assume you don't pepper
it with rat shot. Probably best washed down with a delicate dry white.
----
Reg.

"Reg Edwards" wrote in message
...
If rattle-snake meat is fit for human consumption I assume you don't
pepper
it with rat shot. Probably best washed down with a delicate dry white.
----
Reg.


Tastes just like chicken.
It was a head shot. No spoiled meat. I have JPEGs.
I gave the tail to one of my grad students.
Riesling or Pinot Noir?
H.

Why must engineere resort to quoting from their worshipped Guru's who are
hardly more likely to be correct than they are themslves.

That's easy, because most of the time we have no other choice. When designing
circuits, antennas, troubleshooting, or talking to newsgroups, we have to rely
on other's research. There is no way we can experimentally verify all the data
sheets. charts, graphs, computer programs ect. that are available.
Quoting the last 100 years of antenna research, from worshipped Guru's should
not be a bad thing, because most of us will never have the opportunity to prove
them incorrect. I assume many of the Guru's did the research.
Reg, I am sure you have found numerous errors in Guru's texts, and have tried
to point them out to us. But you cant't just go out in the back yard and burn
all those books:-) Who would we then quote?
73 Gary N4AST

There is no way we can experimentally verify all the data
sheets. charts, graphs, computer programs ect. that are available.

======================================

There's no need to. Inevitably, 99.9 percent of data to be found in books
does not match up to the exact problem in hand. And what is in hand is VERY
exact. Very early in one's career one realises this and soon discovers it is
largely a waste of time 'researching' the literature for details. There's
too much of it. It is more expeditious to have confidence in one's ability,
to go back to first principles and THEN concentrate on the details in
and - which are NEVER to be found in the books.

The best engineers don't have time to write books - except perhaps for
short, simple ones which educate by concentrating on first principles. A
relatively few number of such books or papers are needed. Nearly all of
them have already been written. Such as Shannon's beautifully concise paper
on Ball-packing.

=====================================

Quoting the last 100 years of antenna research, from worshipped Guru's
should
not be a bad thing, because most of us will never have the opportunity to
prove
them incorrect.

====================================

But good engineers accidentally find them incorrect all the time. It forms
part of their normal wasted time. Anybody who worships a book has only ever
read it (e.g. not built the circuit ) - he has never used it in anger. It
has to be admitted that finding more than two errors in a book (not counting
obvious printing errors) is enough to destroy its sacred properties.

====================================

Reg, I am sure you have found numerous errors in Guru's texts, and have
tried
to point them out to us. But you cant't just go out in the back yard and
burn
all those books:-) Who would we then quote?

====================================

I once quoted (second hand) from a text book on this newsgroup. But it was
in an ironical context. Probably nobody noticed.

I possess remarkably few books on radio enginering. One of then is a
treasured 1937 copy of Terman's Radio Engineering. I may refer to it once
every few years because of its comprehensiveness. I have a poor memory. But
I wouldn't dream of using numbers from it in anger without checking from
first principles they are in the right ball park. I remember first
principles. They are so simple and can be expressed in plain English.

But I could not bear to see books of any sort burned! Carry on quoting
Kraus who I am a little familiar with via this newsgroup.

The bottle is finished. Good Night.
----
Reg, G4FGQ

Reg, enjoyed reading your reply, thanks.
73 Gary N4AST

Richard Harrison wrote:
Negative resistance is a gain instead of a loss.

Therefore, doesn't an amplifier have negative resistance?
--
73, Cecil http://www.qsl.net/w5dxp



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