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love machine

Original Poster:

7,609 posts

123 months

[news] 
Friday 22nd December 2006 quote quote all

I know this is a bad idea and have looked at wikipedia for information about cavity magnetrons and it seems they are rather dangerous. I am aware that stray microwaves can cook your corneas. I was debating this fact with a chum the other day. How could you use a microwave guts to kill speed cameras. I know it is a dangerous idea and should not bear fruit, but just for theory's sake, let's debate it.

I rather like the idea of building a "Gun" with flashing lights and a "Woob Woob Woob" sound which kills speed cameras. Taking pot shots at those chaps on motorway bridges. Cooking gatso's.

Now, down to the physics. How do you stop microwaves? I'm well aware that the microwave and it's door creates a faraday cage. How could I shield myself against microwaves produced by my "gun"? Does the cavity magnetron have a decent waveguide to produce a beam? Could I extend this?

I am no way going to build one of these things but quite like the idea that if I really did have the rage I could contemplate building an effective one which would probably be sufficient to do the job.

PJR

2,616 posts

100 months

[news] 
Friday 22nd December 2006 quote quote all

Keep in mind that the speed camera's themselves are already in a metal box so will be quite well protected by that kind of thing already.

P,

Sharief

5,596 posts

104 months

[news] 
Friday 22nd December 2006 quote quote all
I'm going to steal your idea, sell it and make millions.

If it works.

petrol_noggin

3,046 posts

108 months

[news] 
Friday 22nd December 2006 quote quote all
Such "weapons" already exist, the technology has been used in testing by the US military* for 2 decades and has just been put into use for riot roles (a milder version for slowly cooking tree huggers). If it can disable a truck, I can't see why it couldn't stop the glorified polaroids sitting by the roads.

*I realise this point may put the device into doubt for a lot of PHer's but I've got 3 DVD's of the early prototypes being used and it really is incredible.

Edited by petrol_noggin on Friday 22 December 20:35

love machine

Original Poster:

7,609 posts

123 months

[news] 
Friday 22nd December 2006 quote quote all
The microwaves basically cook the radar sensor, snag is the shielding at the business end to protect the user.

I could probably figure out a way of testing whether the device works or not, assuming we weren't just talking theory

I recall diffraction gratings with about a 1cm grating working in a phys lab. However, I'm not sure how much "noise" is produced or whether it is a tight band of frequencies. I suppose I could attempt to build a faraday cage for my head. I had visions of using a microwave door as a kind of "welding mask" but the snag is the door is a part of the F/C and probably wouldn't stop microwaves by itself.

Hmmmm scratchchin
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gilbertd

674 posts

130 months

[news] 
Friday 22nd December 2006 quote quote all
When work was a bit slow one day, we started working on a prototype unit that would cause very loud, screeching noises out of any in car entertainment in any nearby vehicle. The idea was to initially deafen, and then, split the speaker cones of any chav chariot that we may have been sitting nearby in traffic and being forced to listen to his crap. Got as far as causing all the fluorescent lights in the office to illuminate without the power being switched on......

D_Mike

5,301 posts

128 months

[news] 
Friday 22nd December 2006 quote quote all
can't you just have a cube shaped faraday cage with one face missing that lets the microwaves out? or do they not work like that?

ATG

12,422 posts

160 months

[news] 
Friday 22nd December 2006 quote quote all
Anyone know the wavelength of GATSO microwaves? Business end shielding ... if the microwaves' wavelength is 1cm or more, the demisting heating elements embedded in the windscreen might block approriately polarised microwaves from a forward-facing microwave GATSO disruptor. The contents of the engine bay and the rest of the bodywork would probably provide a good enough conducting shield for the rest. Fairly narrow beam can be generated by placing your micorwave generator at the focal point of a suitably sized parabolic dish. You don't want or need too tightly focussed or narrow a beam, as it would become difficult to aim. I assume you're going for a drive-by shooting style ... i.e. screw up measurements from quite a long range, and then melt the receiver as you drive past it.

antony moxey

2,082 posts

107 months

[news] 
Friday 22nd December 2006 quote quote all

Won't you need a really long extension lead, or will it work from some distance away...

bga

7,616 posts

139 months

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Friday 22nd December 2006 quote quote all
It's not just the eyes you need to worry about, you'll need to shield your plums too. If you get wave scatter that covers your body, the happy sacks will get fried first.


You can create your own faraday cage type effect by having a conductive metal mesh with very small holes in.

The mesh allows you to see out, but as long as the holes are much smaller than the wavelength of the microwave then you will be protected as the microwaves will only be able to penetrate a very small distance (due to this you don't want the mesh/shield touching the skin)

tank slapper

7,938 posts

171 months

[news] 
Friday 22nd December 2006 quote quote all
Gatsos operate on 24.110GHz, so rather higher than your average microwave.

You might be able to fry the receiver stage, though I guess it depends on how well filtered it is.

cyberface

12,214 posts

145 months

[news] 
Friday 22nd December 2006 quote quote all

It'd have to be accurately aimable - the metal case of a Gatso will block microwaves, you'll need the microwave beam to get inside the case and resonate, hopefully either frying electronics inside or overheating any part of the mechanism with plenty of hydroxyl bonds in the material.

In terms of shielding the user, surely a cubic or spherical mesh cage around your 'gun' with the barrel (waveguide) pointing out of one end would do the job? Just make sure the mesh cage is earthed and the mesh is sized appropriately considering the wavelength of the microwaves you're generating. You can get detectors cheaply that light up when bathed in 'stray' microwaves (used to test industrial / commercial microwave ovens for leaks) - worth getting a couple to use when developing the 'gun'.

Personally I reckon it'd be worth choosing a wavelength for your EM weapon that induces maximum HF current in the electronics inside the Gatso. I doubt very much whether Gatsos use military spec EM hardened electronics, so all you'd need to do is burn out a few circuits within the apparatus and you're sorted. Even better, if the entire Gatso isn't burnt to a crisp, then the operators are going to have a much harder time diagnosing what's wrong (and hopefully the unit will be out of action for longer).

It's a bit outside my knowledge so I'm not sure if microwaves actually are the best wavelength EM radiation to use to burn out circuits, but surely with enough power, a highly efficient antenna or waveguide that sends *all* the radiation in one beam at the Gatso, you could make a handheld unit that would do the job? I know EMP weapons work well but having to detonate a large amount of explosive inside a coil that only lasts one shot (and wipes all electronics out in the general area, including your getaway car) is a tad inconvenient

A handheld anti-electronics weapon that worked in the way I described would be a damn useful (and very destructive in today's society) device. Perhaps they are very hard to make, which is why I haven't seen too many around....

busta

4,498 posts

121 months

[news] 
Friday 22nd December 2006 quote quote all

All sounds very complicated. Why not just crash into it with a truck?

Then just place a family of toads in the road and say you were swerving to avoid them.

Then microwave the toads and eat the evidence.

Busta

Dunk76

4,350 posts

102 months

[news] 
Friday 22nd December 2006 quote quote all

How does Electronic Counter Measures on military aircraft work?

Remember the story about the copper pointing laser gun at the Harrier? RAF reservist I worked with at the time 'verified' the story and said that the Harrier fried the laser gun with the ECM.



Edited by Dunk76 on Friday 22 December 23:39

tinman0

18,231 posts

128 months

[news] 
Friday 22nd December 2006 quote quote all


scratchchin

tank slapper

7,938 posts

171 months

[news] 
Friday 22nd December 2006 quote quote all
Dunk76 said:

How does Electronic Counter Measures on military aircraft work?

Remember the story about the copper pointing laser gun at the Harrier? RAF reservist I worked with at the time 'verified' the story and said that the Harrier fried the laser gun with the ECM.


That story is cobblers. See here

killer2005

16,188 posts

116 months

[news] 
Friday 22nd December 2006 quote quote all
tinman0 said:


scratchchin


Thats what I was thinking of hehe

mig25_foxbat2003

2,468 posts

99 months

[news] 
Saturday 23rd December 2006 quote quote all
It wouldn't involve a microwave oven, but couldn't you bombard the camera with RF waves on the same frequency, creating loads of spoof images so that it didn't know whether to shoot or not? Or maybe I've been reading too much Tom Clancy.

tank slapper

7,938 posts

171 months

[news] 
Saturday 23rd December 2006 quote quote all
mig25_foxbat2003 said:
It wouldn't involve a microwave oven, but couldn't you bombard the camera with RF waves on the same frequency, creating loads of spoof images so that it didn't know whether to shoot or not? Or maybe I've been reading too much Tom Clancy.


It is a bit more complicated than that. There are different types of radar. Pulse radars transmit a stream of pulses, and measure the time taken to receive a reflection off the target to give a range. Speed is calculated by the difference in ranges over time. To do what you suggest with this type of radar, you would have to transmit a return at the correct time to fool the receiver into thinking it had bounced off something nearby. Not inconceivable, as it was first done in WW2.

Gatsos don't use pulse radar though, they use doppler radar, which means they transmit a continuous wave, and measure the frequency of the reflected signal. The faster the target is travelling, the greater the change in frequency - it is the same effect as hearing a siren change pitch as an ambulance goes past you.

It is probably easier to chuck a tyre over it and set it alight. It can't measure much when it has been melted (not that I'd recommend this of course).

ATG

12,422 posts

160 months

[news] 
Saturday 23rd December 2006 quote quote all
tank slapper said:
Gatsos operate on 24.110GHz
Cool. That's a wavelength of about 12.4mm, so I reckon the windscreen on a Ford Focus, for example, would probably protect you fairly well from any stray radiation, so long as it was polarised. GATSOs are designed to detect a reflected signal. This reflection will be very weak. The GATSO can't be putting out much power, because the yogurt weavers would accuse them of cooking the environemnt. The signal will do the usual 1/r^2 reduction as its cone of radiation expands away from the transmitter in the GATSO, and the reflected signal from the car will do a 1/r^2 over an even wider solid angle after what ever proportion of the incident radiation actually gets reflected. Net result is that the antenna in the GATSO is designed to look for a weak signal. Now if you merrily squirt a couple of Watts of 24.110GHz signal EM back up that antenna, something will go pop. You're not just randomly firing EM into the circuit, you're driving a tuned circuit in the GATSO specifically designed to capture 24.11GHz radiation. Unless they've gone to some effort to protect the first few stages of the antenna's amplifier, something is very likely to go pop. Even if it doesn't, the system will be completely overloaded by the signal and there will be no chance of it detecting the reflected real signal from the car.
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