"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 12:11 PM, John S wrote:
On 11/6/2014 10:52 AM, 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 have not used an equation. I used EZNEC. You can get a free trial
version. It has limitations, but no time limit IIRC.

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?


In receiving, it seems that size matters when it comes to small antennas
like we are discussing.

If you could increase the (receiver) input impedance you will get more
voltage. No matter what you do, you cannot increase the power received
except by refining your system. The (volts/meter)^2 is fixed. It is up
you to capture the available signal. And, I think it will take somewhat
heroic efforts at your frequency of interest.

The power "received" may be a given for the antenna, but the power (or
voltage) delivered to the receiver is not set in the same way.

BTW, have you seen the extremely tiny ferrite rod antennas used in the
so-called Atomic wris****ches?

Yes, but they are not optimal for my application where I need as large a
voltage as possible. If I end up using a preamp I may consider using a
ferrite antenna.

--

Rick

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.


--
Jim Pennino

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

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.

rickman wrote:
On 11/6/2014 12:11 PM, John S wrote:
On 11/6/2014 10:52 AM, 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 have not used an equation. I used EZNEC. You can get a free trial
version. It has limitations, but no time limit IIRC.

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?


In receiving, it seems that size matters when it comes to small antennas
like we are discussing.

If you could increase the (receiver) input impedance you will get more
voltage. No matter what you do, you cannot increase the power received
except by refining your system. The (volts/meter)^2 is fixed. It is up
you to capture the available signal. And, I think it will take somewhat
heroic efforts at your frequency of interest.

The power "received" may be a given for the antenna, but the power (or
voltage) delivered to the receiver is not set in the same way.

The voltage delivered to the receiver is determined by Ohms Law.

The antenna is a voltage source in series with the impedance of the
antenna.

If voltage = E, impedance = Ri, receiver impedance = Rl, then the
receiver voltage is (E * Rl)/(Ri + Rl).



--
Jim Pennino

On 11/6/2014 11:33 AM, rickman wrote:
On 11/6/2014 12:11 PM, John S wrote:
On 11/6/2014 10:52 AM, 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 have not used an equation. I used EZNEC. You can get a free trial
version. It has limitations, but no time limit IIRC.

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?


In receiving, it seems that size matters when it comes to small antennas
like we are discussing.

If you could increase the (receiver) input impedance you will get more
voltage. No matter what you do, you cannot increase the power received
except by refining your system. The (volts/meter)^2 is fixed. It is up
you to capture the available signal. And, I think it will take somewhat
heroic efforts at your frequency of interest.

The power "received" may be a given for the antenna, but the power (or
voltage) delivered to the receiver is not set in the same way.

Yes. I mentioned that a larger impedance load (the receiver input
impedance) would result in a greater voltage. For example, the voltage
available at the receiver terminals in my previous post was 0.001499 V
for the 6' wire and 1000 ohms load. If I now increase the impedance to
1Meg + j0, the voltage is 0.01666 V, more than 10 times as much.

Is that what you mean?

BTW, have you seen the extremely tiny ferrite rod antennas used in the
so-called Atomic wris****ches?

Yes, but they are not optimal for my application where I need as large a
voltage as possible. If I end up using a preamp I may consider using a
ferrite antenna.

Very well, I understand.

John

"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