Microwave gun for remote lowcost instant detonation

[Asger]

(Here goes my first new post as a newbie - hope I'm not still too early)

There is really two issues here : - how to make a functionally portable microwavegun.
- And and then using that gun to set off moving charges. With moving charges I have either spudgrenades or rockets in mind.
This is because I think it could be awesome to detonate a grenade or rocket in mid air at will - and I have seen several ocations where people discussed such capabilities, but never this solution.

The main advantage with this proposal is that the electronics that is sacrificed with the grenade is very cheap and easy to get. The expenses is moved away from the reciever onto the transmitter. The transmitter could even be from a cheap semidefect microwaveoven.

What I would appreciate is first of all your opinions wether this can be done at all or not. I had some very basic theoretic thoughts myself.

As for the microwave gun I was thinking 500 W effective output. (1000 W electrical input ?) Could be driven for shorter periods from a car battery. And all that would be necessary would be a short burst for the detonation.
A sort of perhaps double parabolic antenna would hopefully keep all the radiation within a few degrees. That is i would like an area of say 10x10m at 100 meters to contain all the radiation (5 degrees).

Then all the rocket or grenade would need to carry to detonate the charge would be :
a small powersource eg. a battery or a freshly charged capacitor, a flashbulb in some AP for detonator, a sensitive transistor (MosFet?) and of course an antenna eg. a coil of some sort.
As soon as the antenna picks up the relative (to other electromagnetic fields) powerfull microwaves this pulse will be amplified by the transistor which will dump the energy from the powersource into the flashbulb.

Now if the antenna picks up signal from an effective area of 10 cm2 that would equal something like 5mW out at 100 m. Should be more than enough to trig the transistor. The square area of a 1½" spud gun is about 10 cm2 - suppose you mount the antenna in the butt of the grenade.

Once the microwavegun is ready, it would be fitted with a low x scope (eg. 2,5x) and the mounted along the spudgun or rocketlauncher. When the ordnance is fired you would have to quickly find it around the crosshairs - just within the before mentioned 5 degrees. You then track it and fire a shot of microwaves at it when it is time to detonate it - say if it is about to pass close by but not hit the intended target. Like if you fitted your rocket or grenade with both impact det. and microwave det.

One could even make a timing circuit between the launch trigger and microwavetrigger to have the round explode at a given distance. - Knowing ofcourse the flighttime from tests or calculations.

Cons :
- I have heard that lifetime of magnetrons might be lower when they function outside the cavity of the oven.
- Heavy contraption
- Having to find and lock the flying grenade with a scope yourself.
You probably don't want to mount the microwavegun assembly on the spudgun itself due to recoil but ask your buddy to aim it at the target and be ready to pull the trigger when the grenade closes in on target and thus shows up in the scope.
And don't carry armed grenades of this kind into areas with heavy radiosignals. A cellphone could most likley trig it....

Thanks for listening

<small>[ September 20, 2002, 07:42 AM: Message edited by: Asger ]</small>

[A-BOMB]

Well one thing is parabolics dont work with microwaves because of the wave shape you will have to use a HERF cone. But then I heard of someone using somekind of magnetic field direct the microwaves.

[vir sapit qui pauca loquitur]

i've seen on a few KeWl sites the idea of using magnets, but as far as i can tell, the magnetic power of the common magnet will NOT deflect/warp a microwave projection (for want of a better word).
I have in my kewl days built a microwave briefcase (aviator style case with the guts of a microwave) and from all my tests i was unable to heat a glass of water at about 3 inches !!! but now that i have that more knowledge i would try and go back to get
this working, the only idea that i can suggest would be a microwave wave-guide (cone). if anyone knows the correct length/angle then i would love to hear it.

btw, i used a car battery and an inverter to create the 1000w 240v ac current but it will only work for a short while due to the power being sucked from the battery (about 80 amps !!!) and a car battery is not built to sustain this output for long (i suggest a diesel batt or a marine engine battery due to the higher amp-hour rating (number of hours that it can sustain a 1 amp output or for a short time it's the rate of discharge eg: 85 AH = 85 hours @ 1 amp/ a few moments at 85 amps) the internal resistance of a wet cell is low, but at the higher temperatures generated at high-output this quickly changes making the microwave inoperable due to insufficient current flow
(I=V/R) as R (resistance) increases, the I or current DECREASES

[PYRO500]

The french guy is right, a common magnet won't have a noticible effect on the mocrowave beam. Magnetrons can be bounced off of a parabolic dish but that is gonna be pretty big to get decent gain and complicated. I would recomend a feed horn directly attached to the magnetron itself with a tiny rectangular feed guide for compactness. I am currently constructing a power supply that will pulse the magnetron at around 1.2 KW running on a 9V battery and the entire power supply will lie inside the magnetron's inductor chamber in the back. hopefully I'll be able to design a small horn and make it have enough gain to crash pc's at a reasonable distance.

[Anthony]

Wet cell/car batts won't be too portable. Sealed lead acids would allow a backpack unit. 80A isn't *that* much, but you'll soon knacker a starting battery by running it down to any significant depth of discharge (about 80% remaing or below).

Pyro500, I'd be very interested to hear how you're getting 1.2Kw from what I presume is a PP3 battery? Even in a pulse, it's a lot of power!

[PYRO500]

It's simple, The HV dc module I just ordered is going to charge a small capacitor. The capacitor is going to arc over a spark gap and then give the magnetron a pulse of power. in actuality the average power will be pretty low while the peak pulse power will be pretty high

[the resourceless reaperman]

eehhhmmm,

I'm new so go easy on me here. But does a normal microwave-antenna have the capacity to even make the waves travel further than say 15 inches because it isn't meant to. Even in the microwave itself reflectors are needed to give it sufficient power. My point really is, is 1000Watts really enough, wouldn't it be neccesary to overpower the antenna?

[Voltforce]

An electromagnetic wave can only be focused to its wavelength. For vissible light, a few nanometers is enough focus to burn, but for microwaves which have a wavelength of up to several meters, it is impossible to direct high energy in a certain point without having a high energy magnetron to begin with. A parabolic dish would have to be MUCH larger to better accommodate the longer wavelengths. Microwaves do have the advantage of being very penetrating because molecular structures have a natural resonant frequency that is far different than that of low frequancy radiation (that is why electrons must be manipulated in a vacuum to efficiently create microwaves instead of using other methods that rely on atomic or molecular properties). Conductors however do readily absorb microwave radiation since the wave can be absorbed and made to induce eddy currents within the conductor. This means that if the target has no metal shielding, the electronic components of the target will be overloaded.
Although most military targets are covered in metal, exterior sensors may not be.