Non Radio covert communications

[Lightspeed]

Here's a crazy idea for a simple, covert, non-radio signalling device for communications between fixed locations.

Mount one of the high intensity LEDs in a length of straight metal tube and battery power it via a simple press to make non latching switch. The longer and smaller diameter the tube, the tighter the viewing angle, so the signal will effectively be rifle shot to the desired target.

Such a device could be mounted in a fixed orientation within a roof with the tube exiting through a gable wall etc appearing to be some kind of overflow pipe from outside. It would be aimed at the target receiving location’s fixed observation position.

A portable version could be constructed along the lines of a rifle with the tube mounted on a rifle stock and aimed with an iron or better still a telescopic sight.

Messaging would be by on off flashes. That code would ideally be of our own devise. LED’s which have variable colours could add a third dimension to the signalling possibilities.

Application might be between houses separated, but with clear line of sight between them, between a base and surrounding observation posts. Possibly such a system could be deployed give warning on approach routes to the base whereby from very specific observation points the lamp could be visible (green safe to proceed, Orange , green etc)

Advantage of the system: Very covert, transmitter tube can be hard wired to operate at a considerably remote location form the operator. Simple to construct, durable materials, Low power consumption

Limitation: the system that only work in low ambient light, and in clear, non foggy/rainy/ snowy conditions. Requires electrical supply. Only detectable from very precise locations. Requires ability to decipher transmitted codes.

Employing a mini laser diode would allow the device to function in higher ambient light but is not really suitable as it'd be damaging to the viewers eyesight.

As stated at the start, a crazy idea, but maybe useful to someone one day?

[Highlander]

(20 August 2013, 07:59)Lightspeed Wrote: Employing a mini laser diode would allow the device to function in higher ambient light but is not really suitable as it'd be damaging to the viewers eyesight.

If this is a better idea, the laser could be read via a mirror onto paper

.... I think the idea is sound, but what advantage does it have over a good torch?

[Lightspeed]

(20 August 2013, 08:06)Highlander Wrote:

(20 August 2013, 07:59)Lightspeed Wrote: Employing a mini laser diode would allow the device to function in higher ambient light but is not really suitable as it'd be damaging to the viewers eyesight.

If this is a better idea, the laser could be read via a mirror onto paper

.... I think the idea is sound, but what advantage does it have over a good torch?

Advantage over a torch ( which ist is kind-of) is the much narrower projection angle.

This means more covert operation. Long fixed light tubes would make signalling possible only between very precise locations.

Maybe the laser image being reflected would work.... kind of like the way to look at the sun with a telescope, yes?

[bigpaul]

anything flashing will be seen, and probably a long way off, could end up with a mob of looters coming to investigate.

[Prepper1]

Back to carrier pigeons then.

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what other animals have a homing instinct that are small and reletively easily fed and cared/for stored for use?

[Lightspeed]

(20 August 2013, 10:58)bigpaul Wrote: anything flashing will be seen, and probably a long way off, could end up with a mob of looters coming to investigate.

That's the point of this idea BP the light is onlt visible in a very restricted area.

Its the same principle as was used for landing glide path to small airports. Long light tubes with Orange Green and Red lights in them. You were on the correct glide path if you couls see Green lights at the end of the runway. If en runway lights appeared red you were too low and had to climb.

I agree that lights have to be ised very carefullt as they will attract attention... as I said at the start, just a crazy idea.

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BP If my math is correct, Using a light tube made from 2 meters of 1/2'' plumbing pipe, the beam-width would be around 0.5 degrees, so at 1Km away you'd have to be +/- 15 ft of the beam centre to be able to see the light.

Between two houses 1km apart it is almost certain that the viewing angle can be restricted to just the target house.

Of course lengthening the light tube will reduce the beam-width / viewing angle even further.

[Grumpy Grandpa]

I like this idea LS. Using the tube would make it visible only to your target. There must be quite a few possible applications - just needs imagination!

[I-K-E]

how about an IR laser and use a ir capable camera to view

these can be picked up for not a lot of cash as I found out when looking at home brewed night vision setups ...... not sure about the distance it could work over though

[Lightspeed]

(20 August 2013, 14:01)I-K-E Wrote: how about an IR laser and use a ir capable camera to view

these can be picked up for not a lot of cash as I found out when looking at home brewed night vision setups ...... not sure about the distance it could work over though

Good thought I-K-E

It makes the system more complex but might be feasible

Adding to the complexity, its possible to modilate a laser by ausio frequency, and to capture the signal with a photo-diode over ranges of up to 4 miles.
See http://www.maxmcarter.com/lasrstuf/lasermodulator.html

[Highlander]

Laser is certainly the best way to go, I think the SAS use a simular system to guide aircraft onto targets, as long as you can see the target, be it a tank of your mates up the road, a green laser is very covert

...and depending on how far away your target is, if the laser was on a gun barrel type sight, then your beam could be directed directly into your mates house through a window, and only be seen on an inside wall