Jamming FHSS with DSSS?

[Keego]

One major advantage of FHSS is the fact that it cannot be jammed due to the hopping mechanism it employs. The 802.11 standard switches frequencies every 300ms, requiring a jammer to know what frequency it's on, and what frequency it will be moving to.

A DSSS signal uses up all of these frequencies and spreads the power out. The power difference between FHSS and DSSS is quite large, I understand this. BUT, for interest's sake, would the easiest FHSS jamming method be to have an illegal (in the sense of the FCC's power limits) DSSS signal being broadcast? Is there a more efficient way? Google doesn't really have much in depth about FHSS jamming.

 

[FrankSchwab]

The easiest way to jam a FHSS 802.11 signal is to use a high-powered transmitter broadcasting a signal across the entire 2.4GHz band ( 2.41-2.46 GHz or 5.1-5.8 GHz, IIRC). The transmitted signal would have to be as strong as the 802.11 signal of interest on all the channels simultaneously. This is not a difficult problem in the civilian world. Using a DSSS transmitter accomplishes this task nicely but is more complex than strictly necessary. You would still need to have a large amplifier to boost the normal DSSS signal high enough to effectively interfere with the FHSS signal.

In the military world, having a jamming transmitter that large simply means that you become the biggest target on the battlefield for anti-radiation missiles (radiation in the sense of RF radiation, not Alpha, Beta, and Gamma radiation). When a modern army (not naming names here) invades another country, the first salvoes of missiles are aimed at rf transmitters in the country - civilian broadcasters (radio/TV) as well as Military broadcasters (Command-and-control networks, etc). The easiest way to do that is to launch missiles and/or bombs with rf radiation seeking warheads on them - they see a big transmitter (say the local TV station), they aim for it, and Poof!, the Iraqi Information Minister can no longer get his message across to the populace, and Radio Free (name withheld) is free to transmit their own propaganda / news to the local populace.

 

[Keego]

Thanks, it makes perfect sense that it would be a huge sitting target by having that much of an RF signal go out.



Oh and by the way, the Iraqi Information Minister stopped sending messages because he felt like stopping, not because of some weak bombs that caused no damage 😉

 

[shep7622]

The easiest way to jam a FHSS 802.11 signal is to use a high-powered transmitter broadcasting a signal across the entire 2.4GHz band ( 2.41-2.46 GHz or 5.1-5.8 GHz, IIRC). The transmitted signal would have to be as strong as the 802.11 signal of interest on all the channels simultaneously. This is not a difficult problem in the civilian world. Using a DSSS transmitter accomplishes this task nicely but is more complex than strictly necessary. You would still need to have a large amplifier to boost the normal DSSS signal high enough to effectively interfere with the FHSS signal.

In the military world, having a jamming transmitter that large simply means that you become the biggest target on the battlefield for anti-radiation missiles (radiation in the sense of RF radiation, not Alpha, Beta, and Gamma radiation). When a modern army (not naming names here) invades another country, the first salvoes of missiles are aimed at rf transmitters in the country - civilian broadcasters (radio/TV) as well as Military broadcasters (Command-and-control networks, etc). The easiest way to do that is to launch missiles and/or bombs with rf radiation seeking warheads on them - they see a big transmitter (say the local TV station), they aim for it, and Poof!, the Iraqi Information Minister can no longer get his message across to the populace, and Radio Free (name withheld) is free to transmit their own propaganda / news to the local populace.

can you give an example of how you would do it

 

[John Connor]

Just ask an EA-6B Prowler pilot.

It's RF power...