rickman wrote:
On 11/6/2014 11:08 AM, John S wrote:
On 11/5/2014 7:16 PM, 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?

I ran a simulation to confirm that the received signal is some function
of the length of a wire antenna. My model was a 6 foot zero-loss wire 10
miles from the source with a load of 1000 ohms. The frequency is 1MHz.

Wire length Volts received
6' 0.001499
12' 0.005408

So, it appears that doubling the length of a short antenna captures
about 3.6 times the signal.

Is this what you wanted to know?

That is a nice experimental verification. I guess I figured this is the
sort of thing that there would be an equation for. A loop antenna has a
simple equation defining its effective height (ability to convert the
field to a voltage). I expect there is a similar equation for each
antenna type.

I guess the point is that for receiving it is important to match the
size of the antenna to the signal to receive the maximum power. Or is
there something equivalent to the matching network that would equalize
the power received? In your example you said you used a 1000 ohm load.
Is there a way to improve the signal from the shorter antenna?

All antennas are reciprocal.

One result of that is that if a given voltage at input produces a particular
field, the same field will produce the same voltage upon receiving and
the terminal voltage and field are related by the effective height as
discussed at length in the third link I gave you.

In the second link I gave you it says:

"For an antenna with a symmetrical current distribution, the center of
radiation is the center of the distribution."


--
Jim Pennino

"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?

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?

I will answer your question if you can tell me the efficiency of an
isotropic radiator.

"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?

I will answer your question if you can tell me the efficiency of an
isotropic radiator.

As for all religion, an isotropic radiator is make-believe, and like all
religions, you can make up whatever you choose to be your story.

"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?

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

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.

John S wrote in :

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.


Jim said something the other day that made it clearest for me. He said (of
reciprocity, and not verbatim) that if some field arriving at an antenna
created some electrical signal at its feed point, then recreating that signal
would recreate that field at the antenna itself. My interpretation of that is
that while a receiving antenna, made bigger, captures more energy from a
diverging field from another source, this cannot be equated with transmission
where the whole energy source is transmitted from the antenna regardless of
size if impedance matching is good.