wrote:
For a monopole with uniform current, C=1580
For a monopole with triangular current C= 395

Radiation resistance is four times greater when the antenna has uniform
current.

Reg didn't say "uniform current". He said "uniformly distributed
current". A triangular current wave is uniformly distributed,
i.e. it has a linear taper. Seem to me we need to find out
what Reg meant by "uniformly distributed current". I thought
he meant uniformly triangularly distributed. I think Richard
thought the same thing.
--
73, Cecil http://www.qsl.net/w5dxp

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

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

Gene Fuller wrote:
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.

1.) He could have gotten length correct and assumed current was
triangular. That would reduce radiation resistance by a factor of four.

2.) He could have assumed uniform current and gotten length wrong by a
factor of two, and that would reduce radiation resistance by a factor
of four.

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

Roy, W7EL wrote:
"Do the proper substitutionn and you`ll get the correct answer."

Yes. The warning also appears on page 137:
"In developing the field expressions for the short dipole, which were
used in obtaining (5-56), (5-56) is the value of radiation resistance,
the restriction was made that lambda is much larger than the length of
the dipole L." No problem there, Reg specified a short monopole.

Kraus does a sample calculation for a short dipole. I used Kraus` data
and got the same answer when duplicating his calculation.

But Reg was not asking for an answer to a specific problem. Reg was
asking for the value of the constant in a formula of the same form.
Kraus gives it as 80 pi squared for a dipole.. This is 790.

We know that a monopole has half the resistance of a dipole. Example: 73
ohms and 36.5 ohms. 790 / 2 = 395. That`s not a resistance, it is only
the value of a constant which must be multiplied by (L/lambda) squared
to give the radiation resistance of a very short monopole.

Best regards, Richard Harrison, KB5WZI

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
--

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

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
--

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