| Topic: |
Science > Physics |
| User: |
"" |
| Date: |
17 Dec 2004 04:12:13 PM |
| Object: |
Coherent RF radiation (old man?) |
(sorry if this gets posted twice)
Got some quesions regarding RF radiation, which I know
nothing about. I earlier (not to this group) posted some
question regarding the possibility of RF 'lasers'. At
the time I couldn't see it would be possible to create
an RF laser. The wavelengths of this radiation being so
long that I couldn't envision a 'cavity' large enough
to do this :( I was also told that thermal effects (noise)
would swamp any stimulated emissions at these 'long'
wavelengths.
But now I've been doing some reading on this, and apparently
it is possible, using 'phased arrays'. Supposedly these
use interference effects to direct RF radiation. Neat idea.
How tightly focused can these RF beams be made? I imagine
it's a function of the wavelength... but if EM radiation
really is a particle, one would think it would be possible
to focus things tighter. For example (an extreme example)
would it be possible to focus a 1 Hz wavelength any tighter
than it's wavelength (186,000 miles?)?
Just shows how incomplete our understanding of EM radiation
is, what with all these different models being used to
describe what's going on.
Any links or insights appreciated.
-Eric B
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| User: "Old Man" |
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| Title: Re: Coherent RF radiation (old man?) |
17 Dec 2004 10:09:12 PM |
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<boo@fractalfreak.com> wrote in message
news:1103321533.105091.22870@f14g2000cwb.googlegroups.com...
(sorry if this gets posted twice)
Got some quesions regarding RF radiation, which I know
nothing about. I earlier (not to this group) posted some
question regarding the possibility of RF 'lasers'. At
the time I couldn't see it would be possible to create
an RF laser. The wavelengths of this radiation being so
long that I couldn't envision a 'cavity' large enough
to do this :( I was also told that thermal effects (noise)
would swamp any stimulated emissions at these 'long'
wavelengths.
But now I've been doing some reading on this, and apparently
it is possible, using 'phased arrays'. Supposedly these
use interference effects to direct RF radiation. Neat idea.
How tightly focused can these RF beams be made? I imagine
it's a function of the wavelength... but if EM radiation
really is a particle, one would think it would be possible
to focus things tighter. For example (an extreme example)
would it be possible to focus a 1 Hz wavelength any tighter
than it's wavelength (186,000 miles?)?
Just shows how incomplete our understanding of EM radiation
is, what with all these different models being used to
describe what's going on.
Any links or insights appreciated.
-Eric B
An ordinary RF dipole antenna, fed by a crystal driven RF
transmitter, emits coherent electromagnetic radiation which
is the primary characteristic of a LASER or MASER.
For an array of dipole antennas of overall dimensions, L x L,
rather than improving upon the divergence angle given by,
delta_theta ~ wavelength / L (radians),
careful phasing is required to meet it. You can't beat it.
[Old Man]
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| User: "" |
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| Title: Re: Coherent RF radiation (old man?) |
17 Dec 2004 05:53:33 PM |
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wrote:
(sorry if this gets posted twice)
Got some quesions regarding RF radiation, which I know
nothing about. I earlier (not to this group) posted some
question regarding the possibility of RF 'lasers'. At
the time I couldn't see it would be possible to create
an RF laser. The wavelengths of this radiation being so
long that I couldn't envision a 'cavity' large enough
to do this :( I was also told that thermal effects (noise)
would swamp any stimulated emissions at these 'long'
wavelengths.
Google for "maser", invented 1954.
But now I've been doing some reading on this, and apparently
it is possible, using 'phased arrays'. Supposedly these
use interference effects to direct RF radiation. Neat idea.
How tightly focused can these RF beams be made? I imagine
it's a function of the wavelength... but if EM radiation
really is a particle, one would think it would be possible
to focus things tighter. For example (an extreme example)
would it be possible to focus a 1 Hz wavelength any tighter
than it's wavelength (186,000 miles?)?
Ancient technology; google "phased array" or "AN/TPQ-37" for an example
of real hardware that's been around for about 30 years.
Beam width is measured in degrees, not miles.
Beam width in general is a function of antenna aperature (in wavelengths).
Just shows how incomplete our understanding of EM radiation
is, what with all these different models being used to
describe what's going on.
Any links or insights appreciated.
What do you mean "our understanding"?
Get a copy of the ARRL Antenna handbook for nut and bolt practical
understanding and then a good book on electromagnetics to fine tune
the theory.
--
Jim Pennino
Remove -spam-sux to reply.
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| User: "" |
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| Title: Re: Coherent RF radiation (old man?) |
17 Dec 2004 09:21:09 PM |
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wrote:
(...)
Beam width in general is a function of antenna aperature (in
wavelengths).
Just shows how incomplete our understanding of EM radiation
is, what with all these different models being used to
describe what's going on.
Any links or insights appreciated.
What do you mean "our understanding"?
Get a copy of the ARRL Antenna handbook for nut and bolt practical
understanding and then a good book on electromagnetics to fine tune
the theory.
--
Jim Pennino
Jim,
I thought the beam width would have something to do
with the wavelength of the radiation...
Thanks for the info. Like I say, I don't claim to know
anything about this stuff. Trying to learn.
Glad you've got everything figured out regarding EM radiation.
-Eric
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| User: "Yakovitiz" |
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| Title: Re: Coherent RF radiation (old man?) |
17 Dec 2004 09:30:11 PM |
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<boo@fractalfreak.com> wrote in message
news:1103340069.658034.128430@c13g2000cwb.googlegroups.com...
jimp@specsol-spam-sux.com wrote:
(...)
Beam width in general is a function of antenna aperature (in
wavelengths).
Just shows how incomplete our understanding of EM radiation
is, what with all these different models being used to
describe what's going on.
Any links or insights appreciated.
What do you mean "our understanding"?
Get a copy of the ARRL Antenna handbook for nut and bolt practical
understanding and then a good book on electromagnetics to fine tune
the theory.
--
Jim Pennino
Jim,
I thought the beam width would have something to do
with the wavelength of the radiation...
Both Wavelength and size of the phased array. (Usally stuff is normalized to
wavelength)
Thanks for the info. Like I say, I don't claim to know
anything about this stuff. Trying to learn.
Glad you've got everything figured out regarding EM radiation.
Most all of it is very well known back in the 1980 or before.
Check out Krause, Antennas He did several books.
Google phased arrays
I have about 60 books on EM radiation, antennas, waveguides etc.
It is another subject area for you to learn.
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| User: "" |
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| Title: Re: Coherent RF radiation (old man?) |
18 Dec 2004 12:28:38 AM |
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wrote:
jimp@specsol-spam-sux.com wrote:
(...)
Beam width in general is a function of antenna aperature (in
wavelengths).
Just shows how incomplete our understanding of EM radiation
is, what with all these different models being used to
describe what's going on.
Any links or insights appreciated.
What do you mean "our understanding"?
Get a copy of the ARRL Antenna handbook for nut and bolt practical
understanding and then a good book on electromagnetics to fine tune
the theory.
--
Jim Pennino
Jim,
I thought the beam width would have something to do
with the wavelength of the radiation...
Thanks for the info. Like I say, I don't claim to know
anything about this stuff. Trying to learn.
Glad you've got everything figured out regarding EM radiation.
-Eric
An X wave length antenna for 1 MHz will have the same characteristics
as an X wave length antenna for 10 GHz but will be 10,000 times larger.
To put it another way, a 20db parabola for 10 GHz is about a foot in
diameter, one for 1 MHz would be about 10,000 feet in diameter in round
numbers.
The size of the antenna in wavelengths at the frequency of interest
determines the antenna characteristics.
And, BTW, any antenna fed by a single oscillator would have coherent output.
--
Jim Pennino
Remove -spam-sux to reply.
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