Radiation Resistance
 

On Sun, 12 Mar 2006 12:14:43 -0600, (Richard
Harrison) wrote:

Reg wrote:
"What is the value of the constant C?"

395

It is found on page 137 of Kraus` 1950 edition of "Antennas".


Is that for uniform current as Reg asked?

Owen
--

Radiation Resistance
 

Tom, W8JI wrote:
"You didn`t read something correctly."

OK, here is the arithmetic.

Radiation Resistance of a Short Electric Dipole:

RR = 80 pi squared (L/lambda)squared

Constant = 80 (8.97) = 790

But a short monopole has 1/2 the resistance of a short dipole.

790 / 2 = 395

All Reg asked for was the constant.

Best regards, Richard Harrison, KB5WZI

Radiation Resistance
 

Owen Duffy wrote:
Is that for uniform current as Reg asked?

Reg asked for "uniformly distributed current". I took
that to mean having a constant slope. Wonder what Reg
really meant?
--
73, Cecil http://www.qsl.net/w5dxp

Radiation Resistance
 

On Sun, 12 Mar 2006 20:46:21 GMT, Cecil Moore wrote:

Owen Duffy wrote:
Is that for uniform current as Reg asked?

Reg asked for "uniformly distributed current". I took
that to mean having a constant slope. Wonder what Reg
really meant?

In the context of his use, I think the most probably reasonable
interpretation of Reg's words is that the current is uniform at all
points on the radiator.

Yes, it does also have a constant slope (of zero), so you will ba able
to argue a correct interpetation either way, even if the results are
different.

It was interesting how many different interpretations were made, and
then how many different answers to such a simple questions, even a
text book incorrectly quoted (yes, subject to your interpretation of
Richard's interpretation of what was in Reg's mind. Reg will no doubt
chuckle when he wakes in the morning.

Owen
--

Radiation Resistance
 

Richard,

Your calculation is OK as far as it goes. However, you overlooked the
fact that "L" is different for the dipole and the monopole. The monopole
has 1/2 the length of the dipole or 1/4 the length squared.

The coefficient Reg asked for is therefore 4 times the number you quoted.

73,
Gene
W4SZ

Richard Harrison wrote:
Tom, W8JI wrote:
"You didn`t read something correctly."

OK, here is the arithmetic.

Radiation Resistance of a Short Electric Dipole:

RR = 80 pi squared (L/lambda)squared

Constant = 80 (8.97) = 790

But a short monopole has 1/2 the resistance of a short dipole.

790 / 2 = 395

All Reg asked for was the constant.

Best regards, Richard Harrison, KB5WZI

Radiation Resistance
 

On Sun, 12 Mar 2006 15:06:15 -0600, (Richard
Harrison) wrote:

Owen Duffy wrote:
"Is that for uniform current as Reg asked?"

Reg described a short vertical wire above a perfect ground.

Without a capacitive hat or some such device, you have an open circuit
at the tip of the antenna (zero current) and a finite current at the
driven end of the wire. How would the current be uniform end to end?

That is *your* logic, and on the basis of it, you have chosen to
ignore part of the original question, the explicit statement "the
current in the wire being assumed uniformly distributed", without
qualifying your one word answer.

Owen
--

Radiation Resistance
 

Owen Duffy wrote:
Yes, it does also have a constant slope (of zero), so you will ba able
to argue a correct interpetation either way, even if the results are
different.

OK, I will change my statement to a "constant non-zero
slope". I really think that what's Reg meant but obviously
only Reg's opinion is important on that matter. :-)

Reg will no doubt
chuckle when he wakes in the morning.

:-) When I chuckle with a hangover, it hurts. :-)
--
73, Cecil http://www.qsl.net/w5dxp

Radiation Resistance
 

Richard Harrison wrote:
Owen Duffy wrote:
"Is that for uniform current as Reg asked?"

Reg described a short vertical wire above a perfect ground.

Without a capacitive hat or some such device, you have an open circuit
at the tip of the antenna (zero current) and a finite current at the
driven end of the wire. How would the current be uniform end to end?

For the answer to that, open your Kraus again, and go to the beginning
of the chapter (5) you quoted from. It's explained in the first
paragraph. There's even a picture, Fig. 5-1.

Roy Lewallen, W7EL

Radiation Resistance
 

Richard Harrison wrote:
Tom, W8JI wrote:
"You didn`t read something correctly."

OK, here is the arithmetic.

Radiation Resistance of a Short Electric Dipole:

RR = 80 pi squared (L/lambda)squared

Constant = 80 (8.97) = 790

But a short monopole has 1/2 the resistance of a short dipole.

790 / 2 = 395

All Reg asked for was the constant.


If you'll read more in the chapter of Kraus you're quoting, you'll
notice that L is the length of the dipole, not the length of a monopole.
Do the proper substitution and you'll get the correct answer.

Roy Lewallen, W7EL

Radiation Resistance
 

Roy, W7EL wrote:
"There`s even a picture Fig 5-1"

Yes, exactly as I speculated.

Reg`s question that I tried to answer was:
"What is the value of the constant C?"

My answer is 395 and I`nm sticking with it until someone shows me the
error in my ways.

Best regards, Richard Harrison, KB5WZI