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

On 7/13/2015 3:16 AM, George Cornelius wrote:
In article , Jeff Liebermann writes:
Photon (RF or light) pressure have been measured in the laboratory by
using two pressure gauges, blocking RF and light from one gauge, and
measuring the differential pressure. The differential measurement
cancels external influences, such as gravity, wind, earth movement,
etc.

Maxwell's equations - classical field theory - predict light
pressure even without photons and quantum theory. Double slit
experiments show interference patterns are followed even by
single photons allowed to to pass - exactly as if each photon
converted to a wave and portions passed through each slit and
thus _the photon interfered with itself_.

You really have to observe quantum effects before you can
register individual photons.

And, with e = h nu, nu being frequency, quantum effects at UHF
and below are much harder to see because each photon has such
low energy.

That is the real problem with observing EM photons. IR which has a much
shorter wavelength and higher frequency stimulates molecular motion,
vibration and spinning which is heat. To see even microwave quanta the
apparatus would have to be cooled to very low temperatures to eliminate
the interference.

Do Josephson junctions work at the level of EM quanta? It has been a
long time since I've seen much about them. I don't even remember what
they do except that they are QM phenomenon.

--

Rick

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

There is not any proof that RF behaves differently than light.
Things are already quite complicated without it :-)

Sure there is. After half a century of exposure to RF, my hair is
falling out, my hand is shaking, and my bank account depleted. Other
people, who were only exposed to light, have not had these things
happen. I can only conclude that RF is somehow dangerous and
different from light.


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

On 7/13/2015 10:59 AM, Jeff Liebermann wrote:
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.

I think they have that. They are called radio telescope arrays.

--

Rick

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

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

In article , I wrote:
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.

Actually, the angular spacing increases with N,
so if the dish excludes alias images when aligned
with the overall "optical axis" then it excludes
them when aimed off axis as well.

And I am assuming s w, or the formula gives no
aliasing at all.

George

On 16 Jul 2015 01:18:17 -0400, (George
Cornelius) wrote:

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?

That was the Mark I model. Future models will involve some
miniaturization.

I can't comment on your speculation because (1) I don't know much
about synthetic aperture imaging and (2) it won't work anyway. I
tried to resolve the first problem by doing some light reading on the
topic:
https://en.wikipedia.org/wiki/Aperture_synthesis
What this demonstrated was that either the telescope of the imaged
object needs to be moving. In the case of the optical telescope, it's
the earth's rotation that does the moving. I don't think this is
compatible with an RF eyeball that fits on my workbench. The 2nd
problem is easily solved by what I consider to be a better method. But
first, I need to define an objective in electronic terms.
What I'm trying to accomplish is build an antenna array that
has extremely good resolution, without making it brobdingnagian.
If this can be done with just one antenna system, it could be moved
around in the form of a flying spot scanner to obtain an image,
similar to an optical "flying spot scanner".

The basic problem (for me) is how to get obtain good angular
resolution from an antenna with not so good angular resolution. I
solved this problem with an idea I stole from the WWII Lorenz blind
landing system, using 2 directional antennas or one switched antenna.
https://en.wikipedia.org/wiki/Lorenz_beam
However, I reversed the location of the transmitter and receiver. My
system consists of two identical wide "beams" similar to the beam
pattern produced by any directional antenna. The angular resolution
of the beams causes the amplitude of the signal to vary depending on
it's location along the beam pattern, just like any directional
antenna. By itself, this angular resolution is useless for imaging.
However, if I take two identical antennas, position them at a slight
angle from each other, and switch rapidly between rapidly, the line of
equal signal level half way between them is VERY narrow. In my
testing on VHF, the equal signal null produced was less than 1 degree
wide and could probably be improved with a better test setup. I have
some sketches and photos buried somewhere and will post them if I can
find them.

The circuitry is fairly trivial, consisting of a synchronous antenna
switch and a synchronized AM demodulator charging two capacitors (one
for each antenna), and a comparator. See the block diagram for my AM
homer system:
http://802.11junk.com/jeffl/AN-SRD-21/
http://802.11junk.com/jeffl/AN-SRD-21/Block%20Diagram.pdf

So, how do I produce an image with a null generating derangement? It's
somewhat like a photographic negative, but not quite. It's also great
for direction finding, but not so great for imaging. Simple inversion
of the negative will not produce a usable image. I have some tricks,
but all of them rely on the dynamic range of the AM demodulator, which
frankly sucks, especially in the presence of noise. Reflections also
caused major problems. That's where I stopped working on the idea.

Assuming I can extract an image, a rotating or scanning antenna system
would only produce a line in one axis, which is hardly an image. So,
I propose to store the horizontal line scan, rotate the directional
antennas 90 degrees, and scan again. Where the detected (stored)
voltages in both axes are equal, it produces an output dot. More can
be seen by adding frequency (color) to the output.

While at first glance, this might seem like something thrown together
using WWII technology, implemented with 1970's hardware, and lacking
the benefits of modern acronyms. Yeah, that's probably accurate.
Still, it's something that can be built using technology available to
the average ham. However, instead of using it to RF image a PCB or an
antenna, it might be better to start outdoors by imaging the
neighboring RF environment with a rotating antenna on the roof or
tower. In theory, one could "see" RF sources and reflections off
building and mountains. For indoors, I visualize a motorized X-Y
track mounted on the ceiling, with an antenna array similar to a yagi
pointing downward towards the device under test.

Good luck.

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".

I have an aversion to using a waveguide beyond cutoff for anything
more than a parabolic dish feed. The main problem is the asymmetry of
the pattern caused by the feed being offset from the centerline of the
can. See horizontal pattern:
http://802.11junk.com/jeffl/antennas/coffee2400/index.html

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

On 7/14/15 4:13 PM, Jeff Liebermann wrote:
On Mon, 13 Jul 2015 13:45:43 +0200, "bilou" wrote:

There is not any proof that RF behaves differently than light.
Things are already quite complicated without it :-)

Sure there is. After half a century of exposure to RF, my hair is
falling out, my hand is shaking, and my bank account depleted. Other
people, who were only exposed to light, have not had these things
happen. I can only conclude that RF is somehow dangerous and
different from light.



That's gotta be it, by the infallible principle of Post Hoc Ergo Propter
Hoc.

On Fri, 17 Jul 2015 12:45:52 -0700, Eric Weaver
wrote:

On 7/14/15 4:13 PM, Jeff Liebermann wrote:
On Mon, 13 Jul 2015 13:45:43 +0200, "bilou" wrote:

There is not any proof that RF behaves differently than light.
Things are already quite complicated without it :-)

Sure there is. After half a century of exposure to RF, my hair is
falling out, my hand is shaking, and my bank account depleted. Other
people, who were only exposed to light, have not had these things
happen. I can only conclude that RF is somehow dangerous and
different from light.

That's gotta be it, by the infallible principle of Post Hoc Ergo Propter
Hoc.

Attributing my premature demise to the effects of RF exposure is
nothing new. It's done all the time by those that believe that
correlation is sufficient evidence to assign causation:
http://www.tylervigen.com/spurious-correlations
http://tylervigen.com/discover

It's a form of inductive logic. That's where one makes a series of
observations, and then contrives a generalized conclusion based upon
the available observations. For example, I've noticed that most of
the hams in the local radio club are officially senior citizens.
Therefore ham radio causes accelerated aging. It's all very logical.
The only problem is that inductive logic never really provides a proof
as there are always alternative explanations.

Fortunately, we have an easy test to identify fallacious correlations
called Occam's Razor, where the simplest explanation is usually the
correct explanation. In my case, RF exposure is a far more
complexicated explanation than simple aging. However, I discarded
that explanation due to lack of entertainment value. I also find it
easier to offer an intentionally complex theory that is easily
refuted, so that the simpler theory will be more readily accepted
without contest. Had I initially offered the simple theory, it would
surely have been met by opposition.

I hope this helps.

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