On Wed, 06 Apr 2005 00:37:34 GMT, "
wrote:


"Roy Lewallen" wrote in message
...
Imagine that you put 100 watts into an isotropic radiator in free space
and measure its field strength at some distance. Then you create a ground
plane like the ones used by most modeling programs, perfectly flat and
infinite in extent, and make it perfectly conductive. Now distribute that
100 watts evenly in all directions, above the ground plane -- imagine a
sort of hemi-isotropic radiator which does this. Measure the field
strength at the same distance from the radiator as before.

find that the field strength is 3 dB higher, and the
power density twice as great,

That's interesting! That part regarding change of "density"
How does one determine the density changes in various parts of a radiation
pattern?

Jeeze. You use an rf densiometer of course.

Wes Stewart wrote:
On Wed, 06 Apr 2005 00:37:34 GMT, "
wrote:

That's interesting! That part regarding change of "density"
How does one determine the density changes in various parts of a radiation
pattern?


Jeeze. You use an rf densiometer of course.

An alternate method is to put some of the RF into a water-tight and
RF-tight box -- a great application for one of those ammo boxes left
over from survivalist exercises or just plinkin'. Drop the box into a
tub of water and see how much the water level rises. Then open the box
and let the RF out. (Be sure to wear safety glasses. A shielded cod
piece isn't a bad idea either.) Repeat the measurement. You can then
calculate the power density from the difference between the amounts the
water level rises.

Roy Lewallen, W7EL
(a little late this year, but hey, better late than never)

On Wed, 06 Apr 2005 10:24:58 -0700, Roy Lewallen
wrote:

Wes Stewart wrote:
On Wed, 06 Apr 2005 00:37:34 GMT, "
wrote:

That's interesting! That part regarding change of "density"
How does one determine the density changes in various parts of a radiation
pattern?


Jeeze. You use an rf densiometer of course.

An alternate method is to put some of the RF into a water-tight and
RF-tight box -- a great application for one of those ammo boxes left
over from survivalist exercises or just plinkin'. Drop the box into a
tub of water and see how much the water level rises. Then open the box
and let the RF out. (Be sure to wear safety glasses. A shielded cod
piece isn't a bad idea either.) Repeat the measurement. You can then
calculate the power density from the difference between the amounts the
water level rises.

A takeoff on this method would be to leave the rf in the box and
measure the temperature rise of the water. This eliminates the need
for the cod piece.

I'm really surprised that "The 'ole Metrologist", Richard Clark,
didn't already jump in with this.

On Wed, 06 Apr 2005 10:51:44 -0700, Wes Stewart
wrote:
I'm really surprised that "The 'ole Metrologist", Richard Clark,
didn't already jump in with this.

Is this dance a "mixer?"

Wes Stewart wrote:

Roy Lewallen wrote:
An alternate method is to put some of the RF into a water-tight and
RF-tight box -- a great application for one of those ammo boxes left
over from survivalist exercises or just plinkin'. Drop the box into a
tub of water and see how much the water level rises. Then open the box
and let the RF out. (Be sure to wear safety glasses. A shielded cod
piece isn't a bad idea either.) Repeat the measurement. You can then
calculate the power density from the difference between the amounts the
water level rises.

A takeoff on this method would be to leave the rf in the box and
measure the temperature rise of the water. This eliminates the need
for the cod piece.

I'm really surprised that "The 'ole Metrologist", Richard Clark,
didn't already jump in with this.

Yes, but the question from quantum physics is: Is the RF dead
or alive before you open the box?
--
73, Cecil http://www.qsl.net/w5dxp

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

"corse, what do you do when your Isotropic antenna exibits gain over
your antenna? Does this mean if you stack 2 Isotropics, you have a
gain array ??

Roy Lewallen wrote:
Wes Stewart wrote:

On Wed, 06 Apr 2005 00:37:34 GMT, "
wrote:


That's interesting! That part regarding change of "density"
How does one determine the density changes in various parts of a
radiation pattern?



Jeeze. You use an rf densiometer of course.


An alternate method is to put some of the RF into a water-tight and
RF-tight box -- a great application for one of those ammo boxes left
over from survivalist exercises or just plinkin'. Drop the box into a
tub of water and see how much the water level rises. Then open the box
and let the RF out. (Be sure to wear safety glasses. A shielded cod
piece isn't a bad idea either.) Repeat the measurement. You can then
calculate the power density from the difference between the amounts the
water level rises.

Roy Lewallen, W7EL
(a little late this year, but hey, better late than never)

Jik, NN7K wrote:
"Does this mean if you stack 2 isotropics, you have a gain array?"

This thread has provided many laughs. I`m sorry to to insert a serious,
on my part, posting, but it may bring a chuckle too.

Terman writes on page 874 of his 1955 edition:
"The spacing of the individual antennas in a broadside array has only a
secondary effect upon the directional characteristics of the array
provided the spacing is not too great. Thus, when the individual
antennas are isotropic radiators, vbarying the spacing from very small
values up to 3 lambda/4 affects only the minor lobe structure, as shown
in Fig. 23-11 b."

Best regards, Richard Harrison, KB5WZI

Wes Stewart wrote:

wrote:
That's interesting! That part regarding change of "density"
How does one determine the density changes in various parts of a radiation
pattern?

Jeeze. You use an rf densiometer of course.

To be fair, Art did have a smiley face farther down. The
units of the Poynting Vector are e.g. joules/sec/meter^2.
That's a power density and is the same as "irradiance" in
the field of optics.
--
73, Cecil http://www.qsl.net/w5dxp

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----