"Jeff Liebermann" wrote in message
...

Yep, antennas radiate photons.
+1
There is not any proof that RF behaves differently than light.
Things are already quite complicated without it :-)

On Mon, 13 Jul 2015 13:45:43 +0200, "bilou" wrote:

"Jeff Liebermann" wrote in message
.. .

Yep, antennas radiate photons.
+1
There is not any proof that RF behaves differently than light.
Things are already quite complicated without it :-)

One of my not so great ideas was to devise a contraption that would
let me "see" RF. It certainly would make troubleshooting RF devices
much easier. Essentially, it would be a human eye analog implimented
with RF components. According to theory, if it works for light, it
should also work for RF. At the time, I was working at about 1GHz.
Light is about 400 THz. So, all I need is an eyeball that's 400,000
times larger than the human eye. I'll give myself a -1 for the idea.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...

On Mon, 13 Jul 2015 13:45:43 +0200, "bilou" wrote:

"Jeff Liebermann" wrote in message
. ..

Yep, antennas radiate photons.
+1
There is not any proof that RF behaves differently than light.
Things are already quite complicated without it :-)

One of my not so great ideas was to devise a contraption that would
let me "see" RF. It certainly would make troubleshooting RF devices
much easier. Essentially, it would be a human eye analog implimented
with RF components. According to theory, if it works for light, it
should also work for RF. At the time, I was working at about 1GHz.
Light is about 400 THz. So, all I need is an eyeball that's 400,000
times larger than the human eye. I'll give myself a -1 for the idea.

Wouldn't such a gadget be awesome for adjusting antennas!

On Mon, 13 Jul 2015 08:33:34 -0700, "Wayne"
wrote:
"Jeff Liebermann" wrote in message
.. .

On Mon, 13 Jul 2015 13:45:43 +0200, "bilou" wrote:

"Jeff Liebermann" wrote in message
...

Yep, antennas radiate photons.
+1
There is not any proof that RF behaves differently than light.
Things are already quite complicated without it :-)

One of my not so great ideas was to devise a contraption that would
let me "see" RF. It certainly would make troubleshooting RF devices
much easier. Essentially, it would be a human eye analog implimented
with RF components. According to theory, if it works for light, it
should also work for RF. At the time, I was working at about 1GHz.
Light is about 400 THz. So, all I need is an eyeball that's 400,000
times larger than the human eye. I'll give myself a -1 for the idea.

Wouldn't such a gadget be awesome for adjusting antennas!

Yep. I later realized that it would be marginal for RF circuits
because I could only see the components and traces that radiate RF. If
the circuit was any good, it wouldn't radiate anything.

I also burned some time trying to make an RF equivalent to a liquid
crystal sheet.
http://www.edmundoptics.com/testing-targets/calibration-standards/temperature-sensitive-liquid-crystal-sheets/1642/
Before thermal imagers became relatively inexpensive, I would place a
sheet over the power amplifier or whatever, and be able to see the hot
spots. I was also somewhat successful at creating a blurry thermal
image, using a small germanium lens and one of these sheets.

However, the ideal would be to have a liquid crystal sheet that was
sensitive to RF instead of heat. I couldn't find anything that
detected low frequency RF directly, but did get some interesting
effects by screen printing carbon squares on the thermal sensitive
liquid crystal sheets. The carbon would get slightly warm from the
RF, and cause the color to change. You can also use thermal crayons
to get a similar color change with temperatu
http://www.tiptemp.com/Products/Color-Changing-Thermal-Paint-Crayons/TLCSEN464-245-Color-Change-Crayon-Kit

Long ago, in High Skool, the instructor waved a neon lamp (NE-2) over
a transmission line, so that we could see standing waves. I thought
that was cool, but would be even better if a had a row of neon lamps
so that I didn't need to move the lamp. So, I built one with about
100 NE-2 lamps. Not only could I see the standing waves, but I could
also tune the load for minimum SWR. Today, I could probably built
something similar out of the LED strip lighting on rolls:
http://www.amazon.com/Triangle-Bulbs-T93007-Waterproof-Flexible/dp/B005EHHLD8
However, it would take more power to light up than the NE-2. At 4.8
watts/meter of LED strip, a 20 meter half wave dipole would require 48
watts to fully light at 10 meter long strip.

There are admittedly many things wrong with the aforementioned ideas.
None of them will work because of obvious (and not-so-obvious)
reasons. That's not the point. One has to start somewhere, and
started at "close, but not quite" is as good a place as any.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...

One of my not so great ideas was to devise a contraption that would
let me "see" RF. It certainly would make troubleshooting RF devices
much easier. Essentially, it would be a human eye analog implimented
with RF components. According to theory, if it works for light, it
should also work for RF. At the time, I was working at about 1GHz.
Light is about 400 THz. So, all I need is an eyeball that's 400,000
times larger than the human eye. I'll give myself a -1 for the idea.
Yes it is a question of scale.
There is the trick to use a fluorescent light bulb close to an aerial.
Energy saving lamps can be quite small .
Puting the glass part of one in a microwave oven can be instructive.
Don't forget the cup of water. :-)

In article , Jeff Liebermann writes:
let me "see" RF. It certainly would make troubleshooting RF devices
much easier. Essentially, it would be a human eye analog implimented
with RF components. According to theory, if it works for light, it
should also work for RF. At the time, I was working at about 1GHz.
Light is about 400 THz. So, all I need is an eyeball that's 400,000
times larger than the human eye. I'll give myself a -1 for the idea.

A word: synthetic aperture. Remember the dish arrays in
the Jodie Foster movie Contact? You still need the same
scale factor - many times the wavelength - but most of a
dish array can be air.

So with the eyeball analogy, I would first reduce to the
size of the pupil - the aperture - and that is perhaps
5 mm. Times 400K gives 2000m for the same theoretical
resolution. Of course, for a 2D image you would need
an array of antennas spread over a disk of that radius.

Or just calculate directly. I think the angular
resolution of an array or a telescope in radians is
something like

0.22 * wavelength / aperture .

Multiply by about 60 to get degrees.

So for 1 Ghz (.3m) it's 0.22 * .3m / 2000m, or
33 x 10^-6 radians. About 7 seconds of arc.

George

In article , I wrote:
A word: synthetic aperture.

Drone array, anyone?

[...]

Or just calculate directly. I think the angular
resolution of an array or a telescope in radians is
something like

0.22 * wavelength / aperture .


Oops. That's 1.22 .

Still, I don't think it's too bad considering how
long ago I learned about synthetic aperture
arrays in 2nd year physics.

George

On 7/14/2015 3:21 AM, George Cornelius wrote:
In article , I wrote:
A word: synthetic aperture.

Drone array, anyone?

[...]

Or just calculate directly. I think the angular
resolution of an array or a telescope in radians is
something like

0.22 * wavelength / aperture .


Oops. That's 1.22 .

Still, I don't think it's too bad considering how
long ago I learned about synthetic aperture
arrays in 2nd year physics.

George

Hasn't this problem been solved already? We scan the cosmos with large
radio antenna arrays to form images of celestial features.

--

Rick

On 14 Jul 2015 03:00:32 -0400, (George
Cornelius) wrote:

In article , Jeff Liebermann writes:
let me "see" RF. It certainly would make troubleshooting RF devices
much easier. Essentially, it would be a human eye analog implimented
with RF components. According to theory, if it works for light, it
should also work for RF. At the time, I was working at about 1GHz.
Light is about 400 THz. So, all I need is an eyeball that's 400,000
times larger than the human eye. I'll give myself a -1 for the idea.

A word: synthetic aperture. Remember the dish arrays in
the Jodie Foster movie Contact? You still need the same
scale factor - many times the wavelength - but most of a
dish array can be air.

So with the eyeball analogy, I would first reduce to the
size of the pupil - the aperture - and that is perhaps
5 mm. Times 400K gives 2000m for the same theoretical
resolution. Of course, for a 2D image you would need
an array of antennas spread over a disk of that radius.

Or just calculate directly. I think the angular
resolution of an array or a telescope in radians is
something like

0.22 * wavelength / aperture .

Multiply by about 60 to get degrees.

So for 1 Ghz (.3m) it's 0.22 * .3m / 2000m, or
33 x 10^-6 radians. About 7 seconds of arc.

George

Thanks and interesting. I discarded synthetic aperture imaging
because I assumed that either the sensor array or the object being
imaged had to be moving roughly perpendicular to each other. That
seems to be the case with SAR (synthetic aperture radar). I'll read
some more (later) as I have no experience with the technology.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

In article , Jeff Liebermann writes:
Thanks and interesting. I discarded synthetic aperture imaging
because I assumed that either the sensor array or the object being
imaged had to be moving roughly perpendicular to each other. That
seems to be the case with SAR (synthetic aperture radar). I'll read
some more (later) as I have no experience with the technology.

You mean you were planning a 30,000 foot eyeball and no way to
aim it?

Yes, you are probably right - there would be issues with off-axis
imaging, especially if the individual antennas were widely spaced.

Unfortunately what I know beyond what I talked about is rather
sketchy, but I do know that synthetic apertures are used for
optical telescopes. Instead of a single, perfectly polished
mirror, you place multiple mirrors somewhat distant from one
another and use optical magic (smoke and mirrors?) to put it
all together for form an image.

Anyway, if you have a telescope mirror with holes in it, you
have tradeoffs.

I'm guessing that what happens is that there are
aliasing effects. If the spacing along, say, the
x axis, is s and wavelength is w, you will have
alaising - images of off-axis points that appear
to be on-axis, for example - and I would expect
those to be at angles

arcsin ( N w / s )

relative to the normal (read arcsin as
"the angle whose sine is")

If you want to see something that is off axis, you
might be able to leverage this if each antenna
is directional and blocks most energy from outside
a main lobe narrow enough that, for small N
at least, the antanna only picks up signals from
one of the aliased angles and blocks the adjacent
ones - kind of like an RF amp passband that allows
a desired frequency through and not its image
frequency.

And you might be able to tune the pattern so the
nulls in the pattern at least partially null
out aliases at the N-1 and N+1 angles, where
you would have to have some lobe width adjustment
if you wanted to use this technique for more
than just a single value of N.

If you don't want to use a dish, perhaps you
could use a 'Pringles can' antenna with a dipole
at the far end of a long cylinder - your "telescope
body".

You would feed measured magnitude and phase from
each antenna to your computer to have it produce
an image.

And if you were really good, and used a UHF
illumination source, you would interfere
the illumination source with the received
signals and via holographic techniques
produce true 3D.

Just speculation. But if it's doable I
would guess the military has already done it.

George