Re: garage remote jamming

["Richard Revis" <richard.revis@xxxxxxxxxxxxxxxxxxx>]

"Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote in message
news:WoSdnfla97CuGXXYnZ2dnUVZ_tLinZ2d@xxxxxxxxxx

> Would it work if more than one of those frequencies were deliberately
> jammed?

<delurk>

It depends on how expensive your kit is.

Assuming you have a suitably powerful* frequency agile transmitter then
jamming problem is not easy.

You can either:

Jam every frequency the transmitter is using; If there are up to 20
frequencies you need 20 times as much power as jamming a single frequency
for example.

Hop jamming frequencies when you detect that he has changed transmitting
freqnecy, which means that he can transmit in the interval required for you
to catch up. If the hopping is fast enough you may never catch up.

Attempt to guess which frequency he will use next.  If this is essentially
unguessable - usin a cryptographic RNG or sufficiently complex (and
unrepeated) predetermined pattern for example - then it's very unlikley you
can do this.

If you would like to put in an RFQ for an unjammable garage door opening
device I'm sure we could come up with something - but it might not fit in
your car. (I should point out that neither crypto nor jamming nor
transmitters feature in my job and I am in no way connected to the people
who work here who do that kind of thing, nor am I talking for my employer,
myself, the church, state or any other body with sufficiently deep pockets
to cause me to regret any statement I have made regardless of it's accuracy
or otherwise.)

*In relationship to the reciever, bear in mind the power square law, you
don't need megawatts to get a high recieved power at 5 feet compared to a
transmitter at 5 miles.

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