Posted on 07/11/2009 9:03:57 PM PDT by nuconvert
(Excerpt) Read more at bbc.co.uk ...
Can they work with something covering the dish?
I can’t think of a way to diguise them that they wouldn’t be detected by helicopters flying over.
pong
pong
OK freedom loving engineers, here’s your challenge:
A method of broadcasting voice/data/video from beyond the reach of local governments.
Receiving antennas must be no larger than, say a paperback book, not require physical orientation to the transmitter, work through residential walls or windows and be dirt cheap.
Extra credit for ubiquitous power source.
Extra extra credit for being jam-proof.
Orientation does matter when sending to a satellite. It is probably infeasible to set up a dish inside one of these concrete apartment buildings because the signal would be blocked by the iron reinforcement bars (rebar) inside the concrete. However, a wood frame house might allow operation of an impromptu “dish” made from an umbrella woven with fine wire inside. (Just the kind of thing that an old lady with lots of time on her hands could make, and if someone knocks then the umbrella is closed and the cable yanked.)
Optical modulation of an infrared or ultraviolet light beam might be the best means to smuggle a signal out of the country if near a border.
/johnny
Interesting!
Fascists are always afraid of the truth and free access to information.
I’ve heard recently about micro-networks made from lots of pinhead sized transceivers. They obviously need something like solar power to keep running. Hiding something like this would be harder in a desert than, say, in a woods.
Perhaps a burka?
This — using another radio to generate heterodynes — is something that wouldn’t normally be thought of by people in “free” countries. The “shortwave listener licence” (spelling sic) is needed in the author’s India, but not in the USA.
Where are you _Jim?
Pinhead transceivers?? Hmmmmmm what a Barney Frank speech?? LOL
Dunno, I’ve seen amazing signal pulled from what looks like random noise. DSP chips are getting cheap, and fractal antenna patches progressively more efficient.
Even a modern cell phone is a pretty amazo piece of work. An XM/Sirius class of pocket video/data receiver can’t be impossible. No laws of physics need be violated.
I didn’t ask for bi-directional communication for the masses.
As to unjammable? There’s more than one way to achieve that! For example, if the good guys ‘cuddle up’ to the bad guys’ operating frequencies, it’s ‘Jam me? Jam you!’ time...
Good point. All you need's a high power satellite with sufficient throughput. Signal quality would be less important than content, so you could compress the heck out of the signal. I'm currently receiving Sirius on a 3x3 inch antenna sitting on my desk.
LOL
A Big Burka...
I think he got tired of being beat up all the time...
Actually I think I can design one that looks like a lawn chair.
And not all undeserved — _Jim stood up an awful lot for the Jackboots. In fact, _Jim got awfully livid when I referred to “_Jackboots.” But if anybody should know about radio communication cloak and dagger it would be _Jim.
I imagine that a thatched roof, or mud bricks, or even wooden beams would be fairly transparent to radio, more-so when dry.
Also, why the need for a dish in the first place? That's the solution for when the transmitter is in a fixed location in the sky. Being in a fixed position requires a geosynchronous orbit forcing long distances and requiring much more power at the transmitter end and directional gain on the receiving end.
With a higher powered LEO satellite cloud, some flavor of high power airborne transmitters or over-the-horizon land based transmitters, an omnidirectional antenna might suffice. Someone cleverer than I might be able to make a cheap flat antenna that has some on-the-fly phased array behavior to track a moving source and pick up a little more signal gain.
The key thing is the millions of receivers need to be dirt cheap, while the dozens of transmitters can be more expensive.
IIRC, a broad band unity gain amplifier between the antenna and the local oscillator will prevent the LO signal from feeding back through the antenna. (After 30 years of not doing RF, I'm a little hazy on details)...
LEO satellites are moving rapidly so as one moves out of range another has to move into range continuously. Therefore it takes a lot of satellites to provide continuous coverage making it very expensive. Also, with moving satellites receiving them becomes more complicated for high data rates signals such as video.
LNBs are Low Noise Block converters that do in fact have a high gain low noise amplifier prior to the mixer where the LO (Local Oscillator) is inserted. The LO levels required are much larger than the desired signal level and do leak through the amplifier backwards. All amplifiers have a finite amount of isolation which generally is only a little more than the forward gain. It is possible to add filters in particular to block the LO leakage but this adds significant cost so few if any common LNBs will have one that has very high isolation at the LO frequency. Only the military is likely to have highly isolated LNBs so that they don't give away the location of the user. Another problem is the LO frequencies tend to one of several common frequencies used for that purpose. So you can search for it with a narrow band highly sensitive receiver to find it. It isn't a needle in a haystack so to speak. It is pretty obvious.
Another problem is the LO frequencies tend to one of several common frequencies used for that purpose. So you can search for it with a narrow band highly sensitive receiver to find it. It isn't a needle in a haystack so to speak. It is pretty obvious.
One of my fellow students based his senior project on this. He used a spectrum analyzer to determine what radio station every car passing under a freeway overpass was tuned to.
I suspect he ended up either working for ACNielsen, or is now a spook...
Very high altitude hydrogen balloons acting as transmitting antennae, tethered with an umbilical that contains gas replenishment tube, signal conductor, etc. Balloon carries its own photovoltaic powersource. Materials are radar transparant
Maybe hang a high res recon camera on it too, just for grins.
Lol
If the dishes are too small for that, heads would suffice...
Or even free high altitude balloons.
No need for them to be radar transparent, though. Being transmitters against the radio dark sky makes them as obvious as the Sun, no matter what.
Busy
Booby-trap a couple of them. If these thugs have to approach every satellite dish as if it’s got a pound of C-4 attached to it, things will slow down.
The first two is already achieved Phased array antenna for cars and other vehicles
Remember you are dealing with Basijis. After the first, they will simply force the children of the residents to take the dishs down, at gunpoint.
Still rather large, the smallest is about a foot square, but definitely on the right track (pun intended).
Bi-directional too!
If it follows the usual electronic pattern, the price will be dirt cheap within a decade.
Good to hear. Thanks!
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