I'm kind of new to the world of jamming. I've been trolling for info in the past couple of days on the more technical aspects of jamming and need a bit of help.
I'm a (bored) engineering student from Australia with a fair bit of microcontroller and analog circuits knowledge. I'm fairly confident I can make the required circuitry to recieve and transmit IR effective enough to produce a working jammer. I figured I'd use LED's as they're cheap and they work for blinder so why not?
What I'm stuck with is the way the 'smart jam' works.
In a perfect world, the IR pulse would come in exact intervals so you could predict exactly when the next pulse is due and produce your own pulse to fool the gun into reading a false distance (and hence speed).
Theres a few things that stop this from working...
1. If you moving towards the gun, the timing changes since your closing distance on the gun. This is about a nanosecond every pulse so not a huge concern.
2. A 20MHz Pic microcontroller using its capture module can sample a waveform 5MHz, a 200ns resolution. This completely rules out precision timing.
3. Stealth mode
To address the first I came up with the following -
Use the microcontroller to measure the time between pulses as best you can. Since you can't predict anything with the first two pulses you don't bother jamming them. For the pulses following you spam the interval that you think the pulse will come based on the time between the last two pulses.
Say the pulse timer has a value of 1000, this means the next pulse must come between 1000 and 1001. Since we're limited by the resolution of the timer, you have to start jamming when the timer reachs 1000 and stop when you recieve the real pulse from the gun (to reduce error codes).
Someone posted a picture of the blinder board which showed its little atmel microcontroller. Since there not exactly loaded with insane amounts of processing power, I assume blinder is using a similar algorithm for jamming.
Just a note, the microcontroller wouldn't be generating the timing for the LED's, only when to turn on jamming. The pulse duration would be too short for the uC to do in software so it'd be easier to have an external oscilator to drive the LED.
This still leaves the stealth mode, which will no dout render this type of algorthm useless. I havn't been able to find much info on it but I assume it sends a few pulses and delays a random amount of time and then sends pulses again.
The only way I can see of getting around this is if stealth mode uses a fixed delay's between pulses and a fixed large delay between groups of pulses. Theres alot of processing time between pulses that could be put to use looking for patterns in the pulse timing. Or perhaps if we could get the data, calculating the PPS and loading a profile based on each gun on how best to jam it to reduce error codes.
Can anyone shed some light on this?
Sorry if its a bit confusing, I tried to explain as clear as I can :?