On 11/6/2014 1:19 PM, wrote:
rickman wrote:
On 11/5/2014 10:37 PM, wrote:
rickman wrote:
On 11/5/2014 9:32 PM, wrote:
rickman wrote:
On 11/5/2014 7:28 PM, wrote:
I started to do some modeling on a short antenna for 160M and got what
I think are interesting results.

I will post those as soon as I get a chance to write up all the data.

All this stuff for short antenna is in the context of transmissions,
right? For receiving a short antenna is at a disadvantage, no? I seem
to recall a parameter called "effective height". For loop antenna it
pertains to the signal collected irrespective of the actual dimensions
of the loop. For other types of antenna I assume this is not the same
and does relate directly to the length of the antenna. Is that correct?

All antennas made of linear material are reciprocal in all properties.

The only antennas I know of that include non-linear material are some
microwave antennas with ferrite components.

Generally effective height is the height of the antenna's center of
radiation above the ground.

How do you determine the "height of the antenna's center of radiation
above the ground"?

http://personal.ee.surrey.ac.uk/Pers...nnaheight.html
http://en.wikipedia.org/wiki/Effective_height

In depth treatment:

http://tinyurl.com/lfee64g

I didn't ask for links. I'm asking you for a specific reason.

That is all well and good, but if you look at the last link you will
see the answer is not all that simple.

Your first link relates the effective height to the "actual height"
without explaining just what that is.

Your second link simply states the same words that you used.

They were both simplifications which is why there is the third link.

Your third reference seems to be referring to transmitting antenna and
does not relate this property to the antenna itself.

It is referring to antenas, which are reciprocal devices.

How do you determine the "height of the antenna's center of radiation
above the ground" given the physical parameters of an antenna?

You do all the math shown in the third link, or for simple antennas
you make some simplifying assumptions and get a reasonable approximation
as discussed in the second link.

The effective height is a parameter that indicates the effectiveness of
a receiving antenna. I dug into this for a loop antenna and it is a
function of the diameter, the number of turns and if any magnetic
material is used, the properties of that. I'm wondering what the nature
of the equations are for other antennas?

All the links apply to all antennas.

Yes, I could also start with Maxwell's equations and solve it all
myself. I didn't ask for a complete analysis of an antenna, I asked for
the way that the effective height of a given antenna is determined.

I think the topic is moot now.

--

Rick

On Fri, 07 Nov 2014 10:47:36 +1000, atec77 wrote:

On 7/11/2014 9:31 AM, gareth wrote:
"gareth" wrote in message
...
"John S" wrote in message
...
So, it appears that doubling the length of a short antenna captures
about 3.6 times the signal.

And, therefore, by the reciprocity characteristic, the short antenna
is an inefficient radiator.

So, can I expect an apology from all the Yanks who badmouthed me in
order to try to hide their own ignorance on the matter?



doubtful
you are no matter other mistakes a foolish troll

He's a deeply unpleasant, deliberately disruptive, dunce.

On 11/6/2014 11:33 AM, gareth wrote:
"John S" wrote in message
...
So, it appears that doubling the length of a short antenna captures about
3.6 times the signal.

And, therefore, by the reciprocity characteristic, the short antenna is
an inefficient radiator?

No, not at all. If the kind of reciprocity to which you refer were true,
then the receiving antenna would capture ALL the power radiated. That
obviously cannot be, so I think your idea of reciprocity may be a bit
flawed.

"John S" wrote in message
...
On 11/6/2014 11:33 AM, gareth wrote:
"John S" wrote in message
...
So, it appears that doubling the length of a short antenna captures
about
3.6 times the signal.

And, therefore, by the reciprocity characteristic, the short antenna is
an inefficient radiator?

No, not at all. If the kind of reciprocity to which you refer were true,
then the receiving antenna would capture ALL the power radiated.

Non-sequitur

On 07/11/2014 12:03, John S wrote:
On 11/6/2014 11:33 AM, gareth wrote:
"John S" wrote in message
...
So, it appears that doubling the length of a short antenna captures
about
3.6 times the signal.

And, therefore, by the reciprocity characteristic, the short antenna is
an inefficient radiator?

No, not at all. If the kind of reciprocity to which you refer were true,
then the receiving antenna would capture ALL the power radiated. That
obviously cannot be, so I think your idea of reciprocity may be a bit
flawed.


His whole grasp of antenna theory is flawed.

He was trying to (indirectly) argue the other day via his his
interpretation of Maxwell's Equations you could generate an EM wave
by waving a magnet about. When corrected, he introduced another
variation.

"Brian Reay" wrote in message
...

His whole grasp of antenna theory is flawed.
He was trying to (indirectly) argue the other day via his his
interpretation of Maxwell's Equations you could generate an EM wave
by waving a magnet about. When corrected, he introduced another
variation.

Well, Brian, M3OSN, Old Chum, as was pointed out to you, all of your
posts these days are personal attacks aimed at one or another.

Why do you behave like that?

Certainly, as I corrected myself, if you wave a magnet about fast enough,
say, 1000,000,000 times per second, you will certainly generate an EM wave
and no-one has corrected me on that point because that point is true.

rickman wrote:

snip

Yes, I could also start with Maxwell's equations and solve it all
myself. I didn't ask for a complete analysis of an antenna, I asked for
the way that the effective height of a given antenna is determined.

And I gave you several links that tell you exactly that.

I'm sorry it didn't boil down to a trivial equation.


--
Jim Pennino

On 11/8/2014 1:20 AM, wrote:
rickman wrote:

snip

Yes, I could also start with Maxwell's equations and solve it all
myself. I didn't ask for a complete analysis of an antenna, I asked for
the way that the effective height of a given antenna is determined.

And I gave you several links that tell you exactly that.

I'm sorry it didn't boil down to a trivial equation.

I must have missed that. What I saw was a fundamental analysis of
antennas. Yes, I am looking for an equation similar to what I found for
the loop antenna. Every design of antenna has a similar simple
description.

--

Rick

In rec.radio.amateur.antenna gareth wrote:
"Brian Reay" wrote in message
...

His whole grasp of antenna theory is flawed.
He was trying to (indirectly) argue the other day via his his
interpretation of Maxwell's Equations you could generate an EM wave
by waving a magnet about. When corrected, he introduced another
variation.

Well, Brian, M3OSN, Old Chum, as was pointed out to you, all of your
posts these days are personal attacks aimed at one or another.

Why do you behave like that?

Certainly, as I corrected myself, if you wave a magnet about fast enough,
say, 1000,000,000 times per second, you will certainly generate an EM wave
and no-one has corrected me on that point because that point is true.

No, that point is utterly, completely, and absolutely false and goes
once again to show you have no clue as to the difference between an
electric field, a magnetic field, and an electromagnetic field.


--
Jim Pennino

"gareth" wrote in message
...
"Brian Reay" wrote in message
...
His whole grasp of antenna theory is flawed.
He was trying to (indirectly) argue the other day via his his
interpretation of Maxwell's Equations you could generate an EM wave
by waving a magnet about. When corrected, he introduced another
variation.

Well, Brian, M3OSN, Old Chum, as was pointed out to you, all of your
posts these days are personal attacks aimed at one or another.

Why do you behave like that?

Certainly, as I corrected myself, if you wave a magnet about fast enough,
say, 1000,000,000 times per second, you will certainly generate an EM wave
and no-one has corrected me on that point because that point is true.

I think your arms would start to ache quite quickly.
--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.co.uk