U.S. Embassy Spying - MSNBC Nov 15, 2017 (R Maddow)

On Thursday, November 16, 2017 at 1:55:43 AM UTC-5, snipped-for-privacy@gmail.com wro te:

s (in-depth).

There have always been listening devices and there always will be.

I remember reading the clever way the Russians were snooping on the America ns with no bugs within half a mile of the room: they targeted a laser on a window pane of the room they were spying on. The window pane acted like a m icrophone diaphragm. They then demodulated the return signal which had the room audio modulated on it. Probably not hifi but I'll bet it was usable.

Gotta give them props for that trick.

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cans with no bugs within half a mile of the room: they targeted a laser on a window pane of the room they were spying on. The window pane acted like a microphone diaphragm. They then demodulated the return signal which had th e room audio modulated on it. Probably not hifi but I'll bet it was usable .

** By all accounts, bouncing a IR laser off a widow is not practical. The b eam has to be precisely aligned *square on* to the window and the resulting sound quality is abysmal.

OTOH this simple Soviet invention worked well and had no such issues:

.... Phil

Reminds me of a project , I never got around to trying. I had a pot of those glass beads that are used in the paint of road traffic signs. Since originally thinking about the idea , paint-ball guns are now around. But the idea was to somehow propel a blob of white paste and beads upwards and then down, to splat onto a window pane, leaving a simulated bird shit hit. Then try a laser beam at any angle onto the bird shit and monitor the return.

I don't understand that. Why "square on"? Wouldn't the beam have a tendency to pass right through the glass, with little reflection? Wouldn't it be best to have it meet the glass above the critical angle, so it would experience maximum reflection? Of course, the detector would then have to be well away from the laser, and aligning them would be very difficult.

And in these days of double and triple glazing, it would be even less viable.

Thanks for that link. A very interesting read.

--

Jeff

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** The IR laser and its receiver have to be in the same location, maybe hundreds of yards away rom the target window, so alignment is near impossible.

Google the idea.

.... Phil

This might help: "Laser Bounce Listening Device" See Fig 9 and associated text, which discusses the angles of incidence and reflection.

In my never humble opinion, there are several reasons why it is better to use a laser source and detector at the same location.

1. Any common mode vibration of the laser and detector mounting would cancel if they are mounted on a common surface.
2. It's much easier to build a small interferometer than one with a large baseline.
3. Coated

On the other foot, there is a good reason to use a large reflection angle:

1. Reflections are limited by Brewster's angle. Beyond some angle, al the light is reflected. Below this angle, little is reflected and the laser beam ends up going through the glass and bouncing around the room.
2. Since the reflected light becomes polarized, a polarized filter will reduce optical "noise" pickup from the sun and other sources of light pollution.

I've tried this a few time, but never bothered to try it with dual or triple pane windows. I don't think it will make much difference because I can hear street noises through my double pane windows with little difference over a nearby single pane window. Both panes probably move together.

Yeah, that was really clever. However, I'm told that RF reflections off of anything moving and metallic in the room made listening difficult. At 330MHz, the transmit antenna beamwidth would have covered the entire room and possibly much of the building. Later models worked at microwave frequencies, which offered a narrower beamwidth.

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

That is a good question: can ground-penetrating-emitted waves be bent or co rrupted easier than waves within a laser beam?

Anywho, with a hard-wire connection (on the other hand) like with high-spee d internet, isn't interference more easily detected (and less possible to a pply)? Here, electrodes would have to be applied to the window or some oth er part of both the transmitting and receiving locations. Electrodes (I gue ss) like the ones doctors use to attach to the skull to determine brain sig nals, like if they wanted to merely create the sensation of smoking, drinki ng, doing drugs, etc..) without it actually being done.

How easier RF is refracted (bent) or reflected varies with frequency, material, density, magnetic field, etc. In other words, just about everything you can put between the transmitter and receiver. For GPR, the frequency is important as different frequencies penetrate different materials in varying degrees. This chart sorta helps: If you wanted to go through concrete, I would guess(tm) that 400 Mhz would be about right. I don't have any experience with GPR, so I don't know if this is correct.

However, we're not going through anything. The laser is being reflected off of the surface, probably through a Low-E reduced heat loss coating, and back to a receiver. The ideal surface would be a mirror. The worst surface would be an RF transparent glass or plastic window.

The exact opposite is true for the microphone RF cavity and antenna contrivance. The RF has to penetrate the building or window, reflect off the side of the cavity, go back through the building or window, and somehow end up at the receiver. In this case, the ideal building material would be totally transparent to RF. That's not going to happen, so the best they could do was use lower frequencies, such as

300 Mhz, which sorta goes through building materials. However, the frequency was probably selected because the cavity inside the seal had to be big to pickup voice, and the optimum physical size that would fit worked out to about 300 MHz.

Why would I want to detect interference?

I suspect the embassy staff might have noticed the electrodes and wires. Stealth means a listening device cannot be easily detected.

You just walked off the deep end. I have no idea what you're suggesting or asking. Please bug someone else.

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

Little Gem was not in the Embassy; it was in Spaso House.

-- A host is a host from coast to snipped-for-privacy@nrk.com & no one will talk to a host that's close.......................... Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433

Jeff Liebermann wrote on 11/17/2017 1:47 PM:

I believe you have that wrong. If the laser and detector vibrate the same in the direction toward/away from the reflector, the vibrations add, not subtract.

--

Rick C 

Viewed the eclipse at Wintercrest Farms, 
on the centerline of totality since 1998

What does this have to do with electronics repair? Take it to an appropriate newsgroup.....

Thank you. Here's your official "Junior Net Nazi" badge. (.)

--
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Jeff-1.0 
WA6FWi 
http:foxsmercantile.com

It's one of those ideas that sounds both plausible and really clever except for the small detail that it doesn't work. Like extracting audio from ancient times off the decorative grooves cut into clay pots while spun on a wheel

There are a lot of ways to skin that particular cat, and normal incidence isn't required. Oblique incidence and a remote quad-cell photodiode in another nearby building is perfectly doable. The transmit laser would have a fast 2D scanner, and a separate data link would allow closing a feedback loop to keep the reflected beam centred on the quad cell. What the sound quality would be like, I don't know.

A fast, fine raster scan would allow lock acquisition in a few seconds.

Adaptive optics is used for much harder jobs than that, every day.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
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