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