[Q] TV satellite jamming and prevention techniques
I want to know more about satellite jamming methods, specially the techniques used by Iranian government for censoring TV channels.
According to : http://www-tc.pbs.org/wgbh/pages/fro...SmallMedia.pdf
"Of the two forms of satellite jamming, ?orbital? and ?terrestrial?,
both are frequently used in Iran to prevent access to specific
Persian-language news, information and entertainment
channels broadcast on satellite radio and television from abroad.
Interference is targeted and schematic. Mr Tadjallimehr
continued,"
From my experience the most used technique of the above forms is terrestrial jamming and i want to check if anything can be done to counter its effect.
Can the outside noise be canceled with listening to the noise (with a 360 degrees LNB?) and send the inverted signal back to the input (like noise canceling headphones)? if so, how can i develop such device?
It is practical impossible, due to level energy for Jammer is quite higher if compared to becoming from satellite.
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yes you absolutely CAN null a jammer. You need multiple antennas (like maybe 6 or 9), make them low sidelobe type antennas, and apply the appropriate phase and amplitude weights. I suspect nulling in the 30 to 40 dB range can be achieved. Unfortunately, the signal from the satelliteis pretty small, which make it easy to jam
thank you for the reply and sorry for the noob question. is "Nulling the jammer" a common technique? i really want to know more about this; can you please refer me to a similar designs or maybe an article or a book?
If it's terrestrially sourced interference that attacks your receive
dish, then you might get some relief by shielding everything but
skyward line-of-sight, so that no direct tower radiation can hit
the antenna. You'd be left with only the scattered component.
One crude method is to put your satellite dish in a deep hole! This stops it receiving anything from its spurious side lobes and only picking up the satellite which, hopefully it can see. We used this to stop our transmission dish interfering with terrestrial services.
Frank
Due to the very low-level satellite signals at the terrestrial receiving point, it is relatively easy to achieve jamming. Iranians jam directly the receivers by transmitting a signal at the particular microwave channel from terrestrial transmitters.
Another method they use is to transmit an uplink signal to the satellite. They even jam signals without any relation to Iran.
Defense is almost impossible due to the fact that interfering signal is distributed over a wide area, and the microwave power needed to jam is easy to generate while the antenna to transmit can be even a small monopole. One can design a phased array that can technically reduce the interference but it is very sensitive to minor movements of receiving antennas.
To listen to desired signals is much easier on short-wave bands. The best is to listen to transmissions in English or other than Farsi, but one can use a ferrite antenna on 6 to 18 MHz bands to reduce any jamming by its directionality. By turning the antenna (or receiver with it) in space (also vertically) I succeeded to listen even heavily jammed SW signals using an old Soviet-era radio ORBITA-2.
Who lives in Iran can also jam the official satellite transmissions the same easy way the government jams what one likes most. Changing jammer location is good to do as then it cannot be located. Using more jammers in one location is the best idea.
you are absolutely right! shielding the receiver and putting the dish in the deep hole like pool works perfectly in practice. but the reason i am raising this question is more to check the possibility of developing a relatively easy to use and setup device to block the jammer. for example a method similar to this(?)
I have access to financial assets required to develop and manufacture such device, once i made sure that some sort of method of fighting jamming is possible.
I do not think so! What is described in Wikipedia is a coherent method, not the jammer case. You would have to obtain a perfect copy of the interfering signal, and keep all environment (all metal objects on surrounding buildings) fixed to 1/8 of the wavelength which is ~ one inch. Even moving cars will break your system. No way!
And I am sure the Iranian "sacred" guards of the islamic revolution do follow our discussion here....
you would need to tell us more to get a meaningful answer. For instance what satellite are we talking about. If you know, what frequency, modulation type, transmit power does it have? Approximately how far away is the terrestrial jammer? with that info, we might be able to suggest an actual system.
Also, could be productive take more informations about technique employed on that Jammer to shuffle signal.
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