Hi Mark,
I looked over the thread that your note kicked off.
Unusually, this was not very informative.
People were sticking with antenna measures, which weren't helping much
in this case.

I'll give it a try, introducing the missing concept: energy (and
power) DENSITY.

If you sit in the bright sun for 2 hours, you are likely to get a sunburn.

If you sit in a dark tent, with an opening for a magnifying glass of 2
inch diameter ( = 5 cm), you will get a small burn within 2 minutes.

Looking now at the numbers, you know that the effective power density
of the Sun at the surface is 700 watts per square meter. Your skin
represents say 1.5 sq meters, so you are getting a total power of say 1
kilowatt.
So we are suggesting, at a particular place it takes 1 kilowatt of solar
power for 2 hours to burn you all over.

Now lets look at that dark tent with a hole for a magnifying glass:
the power density at the glass is pi times 1 times 1 inches or pi X .025
X 0.025 square meters = 0.002 sq meters.
The Solar power at the glass is 700w X 0.002 m^2 = 1.4 watts

How the hell can 1.4 watts burn us in 2 minutes, but 1000 watts cannot
burn us in less than 2 hours?

Answer power density:
That 1.4 watts is focussed on a spot that is 1 mm diameter
( 40 / 1000 inch diameter) so its power density is
1.4 / pi X 0.001 X 0.001 watts per sq meter

....and THAT is 446 kilowatts /sq meter.

Oh look: the power density of the spot in the dark tent is about SIXTY
times as great as plain sunlight, so waddaya know, it burns us 60 times
as fast (but only over a LITTLE spot.)

And that's what this thread was all about - the effects of focussing
energy over a particular area.

I hope this helps.

Brian W

MarkAren wrote:
Hi All,

Modern engineering text indicates that for the same frequency, a large
fully illuminated dish will provide more gain than it’s smaller
equivalent. Why is this ?

Consider the following scenario:

======

Take a 10GHz RF source, and attach an appropriate feed horn to fully
illuminate a 2m dia dish.

Adjust focus so that the wave front out of the dish is parallel (2m
diameter ?)

At a distance, arrange the same setup, except the RF source is
replaced by a detector.

Make a note of received signal strength.

======

Repeat the same experiment at the same frequency, but with a
3mdiameter dish at each end, and appropriate feed horns .

Make a note of received signal strength.

======

Also, see http://www.idesignz.org/misc/dishproblem.pdf

In both cases all of the TX energy is transmitted in a parallel beam,
whose diameter is the same as the respective dish.

It would seem that if you can fully convert all of the TX RF into
parallel waves, at some point the diameter of the dishes should not
make any difference to the transfer efficiency of the system.

So, why would the received signal for the 3m + 3m dish be greater than
that of the 2m + 2m dish experiment ?

Thoughts please.

Mark

http://www.idesignz.org/AMPS/AMPS_BS.html – Experimental AMPS micro
Base Station project

http://www.idesignz.org/UAV/index.html – Early work on the four rotor
FlyingThingy

On Oct 16, 5:08*pm, brian whatcott wrote:
Hi Mark,
I looked over the thread that your note kicked off.
Unusually, this was not very informative.
People were sticking with antenna measures, which weren't helping much
in this case.

I'll give it a try, introducing the missing concept: * energy (and
power) DENSITY.

If you sit in the bright sun for 2 hours, you are likely to get a sunburn..

If you sit in a dark tent, with an opening for a magnifying glass of 2
inch diameter ( = 5 cm), you will get a small burn within 2 minutes.

Looking now at the numbers, you *know that the effective power density
of the Sun at the surface is 700 watts per square meter. Your skin
represents say 1.5 sq meters, so you are getting a total power of say 1
kilowatt.
So we are suggesting, at a particular place it takes 1 kilowatt of solar
power for 2 hours to burn you all over.

Now lets look at that dark tent with a hole for a magnifying glass:
the power density at the glass is pi times 1 times 1 inches or pi X .025
X 0.025 *square meters = 0.002 sq meters.
The Solar power at the glass is 700w X *0.002 m^2 = 1.4 watts

How the hell can 1.4 watts burn us in 2 minutes, but 1000 watts cannot
burn us in less than 2 hours?

Answer power density:
That 1.4 watts is focused on a spot that is 1 mm diameter
( 40 / 1000 inch diameter) so its power density is
* 1.4 */ pi X 0.001 X 0.001 watts per sq meter

...and THAT is 446 kilowatts /sq meter.

Oh look: the power density of the spot in the dark tent is about SIXTY
times as great as plain sunlight, so whaddaya know, it burns us 60 times
as fast (but only over a LITTLE spot.)

And that's what this thread was all about - the effects of focusing
energy over a particular area.

I hope this helps.

Brian W



MarkAren wrote:
Hi All,

Modern engineering text indicates that for the same frequency, a large
fully illuminated dish will provide more gain than it’s smaller
equivalent. Why is this ?

Consider the following scenario:

======

Take a 10GHz RF source, and attach an appropriate feed horn to fully
illuminate a 2m dia dish.

Adjust focus so that the wave front out of the dish is parallel (2m
diameter ?)

At a distance, arrange the same setup, except the RF source is
replaced by a detector.

Make a note of received signal strength.

======

Repeat the same experiment at the same frequency, but with a
3m diameter dish at each end, and appropriate feed horns .

Make a note of received signal strength.

======

Also, seehttp://www.idesignz.org/misc/dishproblem.pdf

In both cases all of the TX energy is transmitted in a parallel beam,
whose diameter is the same as the respective dish.

It would seem that if you can fully convert all of the TX RF into
parallel waves, at some point the diameter of the dishes should not
make any difference to the transfer efficiency of the system.

So, why would the received signal for the 3m + 3m dish be greater than
that of the 2m + 2m dish experiment ?

Thoughts please.

Mark

http://www.idesignz.org/AMPS/AMPS_BS.html– Experimental AMPS micro
Base Station project

http://www.idesignz.org/UAV/index.html– Early work on the four rotor
FlyingThingy- Hide quoted text -

- Show quoted text -

A good read thank you.
A bit lengthy; but well done.
While illuminating the subject it does focus attention on the
important point; the 'beaming' or directionalizing of the available
energy, whether it be sunlight or any other frequency.
However there will always be some who 'can't' or 'won't' understand.
Witness some of the nonsense that is posted on various news groups all
the time.
PS. That 700 watts per sq. metre is an interesting number? Bright sun
at midday at the equator perhaps?
But I doubt that here at around 48 degrees north and with our climate
we get anything close to that?
Also now wondering how efficient a solar panel is at converting that
700 watts into electric power (for say home use). Which may be why
some 'solar' collectors are both photo-voltaic and heat collecting.

terry wrote:
....
Looking now at the numbers, you know that the effective power density
of the Sun at the surface is 700 watts per square meter. Your skin
represents say 1.5 sq meters, so you are getting a total power of say 1
kilowatt.

.....
That 700 watts per sq. metre is an interesting number? Bright sun
at midday at the equator perhaps?
But I doubt that here at around 48 degrees north and with our climate
we get anything close to that?
Also now wondering how efficient a solar panel is at converting that
700 watts into electric power (for say home use). Which may be why
some 'solar' collectors are both photo-voltaic and heat collecting.

The scientific name for this measure is Solar Irradiance. If you hold up
a square frame 1 meter on a side, perpendicular to the Sun's direction,
in space near Earth's orbital distance, about 1400 watts passes the
frame - and twice as far from the Sun, that frame only frames a quarter
of that amount (of course!)

That number 700 W/m^2 takes into account the absorption of power by
stuff in the atmosphere, more at slant angles of course.

This URL can show the kind of Solar power you can expect at various
geographical coordinates.
http://re.jrc.ec.europa.eu/pvgis/apps/radday.php

You'll see a peak value around noon - and this can be more than 700
W/m^2 at that 48N latitude.

Brian W

Hey OM

If I look at the node of a source of 20mW and connect 10 wires to that
node with equal loads, I will have 2mW going down each wire. No matter
how I try and add them up I can't get more than 20 mW.

Now I take a 20 mW isotropic emitter, now your'e saying I feed a dish
with that 20mW emitter through a feed horn and now all of a sudden I
have gain, I have more than 20 mW? Because the dish and feed horn are
able to add the particles and waves, where as with 10 wires I cannot
add the waves and particles?

The only difference in both these are the shape of the dish and the
medium used to convey the wave, particles.
And you can add the waves particles until you run out of dish.


73 OM
de n8zu



On Oct 18, 8:40 pm, brian whatcott wrote:
terry wrote:

...

Looking now at the numbers, you know that the effective power density
of the Sun at the surface is 700 watts per square meter. Your skin
represents say 1.5 sq meters, so you are getting a total power of say 1
kilowatt.

....
That 700 watts per sq. metre is an interesting number? Bright sun

at midday at the equator perhaps?
But I doubt that here at around 48 degrees north and with our climate
we get anything close to that?
Also now wondering how efficient a solar panel is at converting that
700 watts into electric power (for say home use). Which may be why
some 'solar' collectors are both photo-voltaic and heat collecting.

The scientific name for this measure is Solar Irradiance. If you hold up
a square frame 1 meter on a side, perpendicular to the Sun's direction,
in space near Earth's orbital distance, about 1400 watts passes the
frame - and twice as far from the Sun, that frame only frames a quarter
of that amount (of course!)

That number 700 W/m^2 takes into account the absorption of power by
stuff in the atmosphere, more at slant angles of course.

This URL can show the kind of Solar power you can expect at various
geographical coordinates.http://re.jrc.ec.europa.eu/pvgis/apps/radday.php

You'll see a peak value around noon - and this can be more than 700
W/m^2 at that 48N latitude.

Brian W

raypsi wrote:
Hey OM

If I look at the node of a source of 20mW and connect 10 wires to that
node with equal loads, I will have 2mW going down each wire. No matter
how I try and add them up I can't get more than 20 mW.

Now I take a 20 mW isotropic emitter, now your'e saying I feed a dish
with that 20mW emitter through a feed horn and now all of a sudden I
have gain, I have more than 20 mW? Because the dish and feed horn are
able to add the particles and waves, where as with 10 wires I cannot
add the waves and particles?

The only difference in both these are the shape of the dish and the
medium used to convey the wave, particles.
And you can add the waves particles until you run out of dish.


73 OM
de n8zu


Actually your example tends to prove the point that you're questioning.
10 points of 2mw DO add up to 20 mw.

The difference with an isotropic radiator is that there are an infinite
number of points each at say 20mw. Add 'em up by focusing those points
into a single path.

If you can rationalize a 20mw transmitter feeding one direction down a
feedline or waveguide and still getting 20mw EIRP in ALL directions with
an isotropic radiator then it should make sense.

-Bill

raypsi wrote:

Hey OM

If I look at the node of a source of 20mW and connect 10 wires to that
node with equal loads, I will have 2mW going down each wire. No matter
how I try and add them up I can't get more than 20 mW.

Correct.

Now I take a 20 mW isotropic emitter, now you're saying I feed a dish
with that 20mW emitter through a feed horn and now all of a sudden I
have gain, I have more than 20 mW?

Not exactly, I am saying you have a gain in power DENSITY
i.e watts per sq meter. In a desired direction only, naturally.

Like when you use a magnifying glass to collect the Sun's power into a
small spot.

73 OM
de n8zu

Hey OM:

I tell you what. I took just 1 particle wave and shoot the particle
wave into a 60db dish. At the focus I got 1,000,000 partivle waves. I
mean that is 60 db right?

So where did the other 999,999 particles come from? Energy density
from focusing just one particle?

The two slot experiment buttresses the above.

Take 2 parallel slots shoot just one particle wave into just one slot
and 2 particle waves come out the other side.

73 OM
de n8zu

Take a small light bulb, it shines light in many directions.

Place this at the focal point of a mirrored parabolic dish and the
light is predominantly directed in one direction.

In the direction that the dish is pointing, and at a distance, measure
the received light using a light meter.

Remove the dish, and at the same distance, measure the received light
using a light meter from the naked bulb.

One measurement will be higher than the other.

Why do you think this might be ?


On Oct 24, 5:24*am, raypsi wrote:
Hey OM:

I tell you what. I took just 1 particle wave and shoot the particle
wave into a 60db dish. At the focus I got 1,000,000 partivle waves. I
mean that is 60 db right?

So where did the other 999,999 particles come from? Energy density
from focusing just one particle?

The two slot experiment buttresses the above.

Take 2 parallel slots shoot just one particle wave into just one slot
and 2 particle waves come out the other side.

73 OM
de n8zu

raypsi wrote:
Hey OM:

I tell you what. I took just 1 particle wave [ per sq meter] and shoot the particle
wave into a 60db dish. At the focus I got 1,000,000 particle waves [ per sq meter]. I
mean that is 60 db right?

Yes.

So where did the other 999,999 particles come from? Energy density
from focusing just one particle?

NOW, you're getting it! No more particles, but more particle density,
when the flux is directed tightly...



The two slot experiment buttresses the above.

Take 2 parallel slots shoot just one particle wave into just one slot
and 2 particle waves come out the other side.

73 OM
de n8zu

Actually no. But you probably realized that. Or did you?

I am not pursuing this much further, because you are starting to respond
like a person who wants to drag out an argument.

Listen to me when I say: "I can be wrong. I often am."

Can you say that too, with some sincerity? :-)

Brian W

:-)

Nice concrete example, Mark.
The same conclusion holds if the bulb is so dim, that it only emits one
photon at intervals.

Brian W

MarkAren wrote:
Take a small light bulb, it shines light in many directions.

Place this at the focal point of a mirrored parabolic dish and the
light is predominantly directed in one direction.

In the direction that the dish is pointing, and at a distance, measure
the received light using a light meter.

Remove the dish, and at the same distance, measure the received light
using a light meter from the naked bulb.

One measurement will be higher than the other.

Why do you think this might be ?


On Oct 24, 5:24 am, raypsi wrote:
Hey OM:

I tell you what. I took just 1 particle wave and shoot the particle
wave into a 60db dish. At the focus I got 1,000,000 partivle waves. I
mean that is 60 db right?

So where did the other 999,999 particles come from? Energy density
from focusing just one particle?

The two slot experiment buttresses the above.

Take 2 parallel slots shoot just one particle wave into just one slot
and 2 particle waves come out the other side.

73 OM
de n8zu