Afghan Bridge Update and Sad News

Bill sez:

"2. disassemble microwave oven, make horn to direct micorwaves downward, move the device (fairly slowly) over suspect ground - microwaves are likely (not guaranteed) to hurt detnoation electronics"

But be very careful when carrying the microwave oven with the long extension cord. The extension cord may drag over and detonate one of the devices or you may step on one. Advice not up to Bill Nobles usu. standards.

Bob Swinney

snipped-for-privacy@yahoo.com wrote: (...)

(...)

I like your first idea a lot, Ken.

If you knew the electrical resonant frequency of the initiator, you could aim a parabolic dish off a boom in the front of a vehicle. A high power transmitter tuned to that resonant frequency would drive several

10's of megawatts of ERP down into the cap, bypassing the trigger. Dishes and transmitters are cheap!

--Winston

Metal pressure plates that big and buried shallow would be very easy for a metal detector to find, and the detector could be desensitized so it didn't pick up miscellaneous small bits like shrapnel etc.

A metal detector would be small enough and light enough for a small R/C vehicle to handle, and they draw very little power.

Very, very unlikely. There's no closed circuit in the described IED in which to induce current, and the field of a metal detector is very weak.

The only way I know of that an EM field can fire a squib is if it's high enough in frequency (and powerful enough) to induce enough resonant RF current in the squib leads. Resonance doesn't require a closed circuit. That'd be at least UHF in frequency, and at least a couple of watts of power -- and then only if the metal pressure plate doesn't act as an effective RF shield. Metal detectors typically operate at kilohertz or low megahertz frequencies.

My understanding is that the frequency needed depends on the length of the wires going to the det. And that about 27 MHZ is about right.

Dan

The idea is to cause inductive heating of the of the squib, yes? There is no current path via the leads unless you can convince the enemy to install (say) a capacitor across their series switch.

--Winston

At RF frequencies where the squib leads form a half-wave dipole, no other current path is necessary. The squib itself would be the current path and electrical load. 27 MHz would require rather long squib leads, as might be found in mining, construction or demo setups. Twisted parts don't count much, but eventually they must separate enough to engage a switch and battery within an IED.

I understand. So perhaps an FM microwave power oscillator feeding a downward facing parabolic antenna? Lots of ERP at all the reasonable frequencies? Sounds like something worth testing.

--Winston

You mean besides putting one vibratory soil compactor into low earth orbit? 8-O

Call NORAD so they can track the trash... On second thought it probably won't make escape velocity, but "What goes up must come down" still applies. It's got enough mass to go right through whatever house or car roof it lands on. Headache!!

That's the nifty thing about a mine flail, the arm is just far enough away that it should remain attached and mostly undamaged. You'll lose some of the chains and flail weights in the BOOM!, but they won't go nearly as far.

-->--

How well do the thermal imaging night-vision cameras work in the field? I built some telescopic lenses for them, about the size of a gallon paint can with black Germanium front elements, but never heard anything good or bad about them from the field.

After a Computer crash and the demise of civilization, it was learned Gunner Asch wrote on Sun, 18 Nov 2007

11:52:18 -0800 in rec.crafts.metalworking :

And thanks tot he NYT and the rest of "Al Majnoon", the terrs know about the jamming. So, back to Bell Telephone wire.

tschus pyotr

"Al Majnoon" is Arabic for "The lunatics", Literally "those possessed of a djinn (evil spirit)."

-- pyotr filipivich "Quemadmoeum gladuis neminem occidit, occidentis telum est. " Lucius Annaeus Seneca, circa 45 AD (A sword is never a killer, it is a tool in the killer's hands.)

Don sez:

"Very, very unlikely. There's no closed circuit in the described IED in which to induce current, and the field of a metal detector is very weak.

The only way I know of that an EM field can fire a squib is if it's high enough in frequency (and powerful enough) to induce enough resonant RF current in the squib leads. Resonance doesn't require a closed circuit. That'd be at least UHF in frequency, and at least a couple of watts of power -- and then only if the metal pressure plate doesn't act as an effective RF shield. Metal detectors typically operate at kilohertz or low megahertz frequencies."

Yes - very unlikely indeed. At 400 mHz at a distance of 2 feet it would take

200 Watts of power to couple 2 watts into the device; and this assumes no shielding of any kind in the 2 foot path. In other words 200 watts of RF will be attenuated by free space loss down to 2 watts at a distance of 2 feet.

This based on the free space loss formula: FSL = 36.6 + 20 Log D (in miles) +

20 Log F (in mHz)

Bob Swinney

Right. 27 mhz is about 11 meters so for a half wave length dipole each wire would be about 9 feet. This is what I vaguely remember from some classes. If you want better information search on " HERO safe ordnance ".

Dan

Now it becomes political. Try and find DARPA funding to do any such research! Hm, I think my pass to the ordnance proving grounds near St. Francis has expired -- about 30 years ago.

Don sez:

"Very, very unlikely. There's no closed circuit in the described IED in which to induce current, and the field of a metal detector is very weak.

The only way I know of that an EM field can fire a squib is if it's high enough in frequency (and powerful enough) to induce enough resonant RF current in the squib leads. Resonance doesn't require a closed circuit. That'd be at least UHF in frequency, and at least a couple of watts of power -- and then only if the metal pressure plate doesn't act as an effective RF shield. Metal detectors typically operate at kilohertz or low megahertz frequencies."

Yes - very unlikely indeed. At 400 mHz at a distance of 2 feet it would take

200 Watts of power to couple 2 watts into the device; and this assumes no shielding of any kind in the 2 foot path. In other words 200 watts of RF will be attenuated by free space loss down to 2 watts at a distance of 2 feet.

This based on the free space loss formula: FSL = 36.6 + 20 Log D (in miles) +

20 Log F (in mHz)

Bob Swinney

And the first (admittedly silly) thing that flashed through my head...

"Breaker One Nine, this here's the Rubber Duck. Hey Pig-Pen, you got your ears on?..." -=++=-

The RF is to induce electrical current in the squib leads, and that current would be the source of the heat to trigger the squib.

And if it doesn't work for that, a 10KW focused microwave beam certainly will BBQ any roadkill in front of the antenna. ;-)

A properly designed explosive device has the squib leads twisted, shielded and grounded out, RF shielding and bypass capacitors, and other things done deliberately to keep stray RF signals out of the trigger circuit, and all that protection stays in place till the last possible second. Since premature detonation isn't too healthy for the bomb builders or the delivery crew.

But IED's are nothing like properly designed explosive devices, so potentially large doses of RF at the right frequencies could work. At least till they figure out how we're defeating them...

-->--

I would be amazed if simple "wrap it in foil and use twisted wire" approach did not 100% prevent premature detonation through any kind of RF generator.

i

Are you saying that the New York Times, CNN (Clinton News Network) and other Leftie Loonie US news outlets are deliberately leaking military secrets on how we're getting a leg up on Al Queda, so the other side can stop doing those things? As Captain Renault would say "I'm SHOCKED!"

Not.

Like how Osama Bin Ladin stopped using his satellite phone the second word leaked out we had his number? And we could have dropped a cruise missile in his lap simply by homing in on it?

"Freedom of the Press" only works with a responsible press. And responsible means you don't give out operational details that can affect the outcome while the game is still afoot.

We invented Spread Spectrum frequency hopping scrambling in WW-II, and many other technological advances that greatly shortened the war. But word didn't get out about most of them till much later - and that was entirely on purpose.

-->--

(...)

I can't help with that problem but I think your 'mine roaster' is an excellent idea.

--Winston