This could be a general question, but I’m not sure, so I’ll put it here for now.
Most of us know (and those who didn’t, do now) that the microwave-oven principle was discovered by engineers at Raytheon while developing and testing military radars. The candy bars in their pockets happened to melt when they walked past the microwave tubes (okay, maybe not, but they did notice bag luches and such heating up when left on the desk in front of the things).
The big SPY air-search radars on the US Navy’s Aegis cruisers are insanely powerful. These things can send up to seven million watts of RF energy down half a degree of bearing. That’s lots of watts. Enough, in fact, to burn out electronics out to 5 miles or so–the technical term for this phenomenon is “zorch”.
Anyway, to the question:
What would happen if you put, say, a 22-pound frozen Butterball turkey in front of one of these things and turned it on? How fast would it cook?
What about an unlucky pilot that happened to fly through the cone at max power and min spread a mile or two away from the ship? Would he cook in his seat, or just have to buy a new watch? (the latter, BTW, is almost a given)
Well, I knew this info would come in handy someday…
Worked as a radar engineer for Westinghouse (now Northrop Grumman) for a number of years on the airborne radar thingees. The old timers used to put popcorn in the radomes to pop it - mostly for “fun”, I think.
To answer your questions:
Parts of it would cook, parts of it wouldn’t. The “beams” are very focussed (but move or “scan”), so the parts of the turkey that were in the beam’s “path” would eventually cook somewhat. (Surrounding parts would cook from the nearby heat, too.) Wouldn’t be very fast. Wouldn’t be very efficient. Would be VERY messy. (Popcorn worked well, I assume, because each individual piece is quite small and once popped was “done”.)
Yes they do get “irradiated”, just like you and I do every day (by lower power TV and radio signals, which are the same thing - RF waves - only at different frequencies and powers). Radar signals, while stronger, dissipate very rapidly - exponentially, actually - with distance, like all RF. Therefore once you’re even a little distance away, the signal is very weak (in terms of "cooking, though strong enough to do the intended job). People on the flightline (usually techs/crew chiefs and not pilots) walk through these beams all the time (by accident, usually).
Though it might happen, I’ve never heard of the watch phenomenon, and certainly not of any other kind of human cooking. I did once find a cracked waveguide by having the hair on my arm stand straight up, though.
And then there’s the weird phenomenon of (male) RF Engineers fathering only girls…
Yeah, I know the “airborne thingies” wouldn’t work too well for cooking, but I’m talking about the ridiculously powerful Aegis radars…these things are pumping out more RF power than most radio stations…but I do see your point.
And, we are, for the purposes of this discussion, putting the turkey on a rotisserie that is being spun by remote control from a safe distance.
>> can send up to seven million watts of RF energy down half a degree of bearing
Nope, no way. My boat’s radar is termed 1.5 Kw and yet consumes under 4A @12VDC. It consumes under 50w and there’s no way it is putting out 1.5 Kw… What it is putting out is pulses that last 0.5 uS and repeat at 750 Hz. Do the math and you will see it transmits 375 uS out of every second which means it is putting out less than 0.56 watt.
The seven million watts may be peak power of pulses but there is no way in the world any radar is putting out that kind of energy or anything close to it.
I seem to remember the book MiG pilot (About Bilinko’s escape to Japan in a MiG-25) mentioning that the radar on the MiG had to be turned off on the ground because it would kill small animals. But am not sure aobut that.
However, I do remember something from the first time I was in Bldg 620 at WPAFB where my mother worked (I worked there as well, years later, but this is earlier.) and getting a chance to see the radome they had on the roof. In the radome they had three small radar or microwave dishes, and a single large commdish. They had earlier in the week lost track with one of the smaller dishes, and it had turned to far upwards before they could shut it down. You could trace its path from the fact that the paint on the larger dish had started to bubble where the beam had hit.
Just for the sake of argument (and because I happen to have my Krack manual open on a page with frozen turkey info on it while I read the question) I did some rough estimates of the cooking time. Assuming the turkey’s initial conditions are 22 lbs, about 20 deg F, 57% moisture and frozen solid, and it’s final conditions are an average temp of 180 deg F (higher in the outer areas, lower center temp about 155) with a total moisture content of about 30%, with the moisture removed leaving as vapor, it would require only about 4930 Btu. Assuming 100% of the 7MW went into the turkey, it would cook in about 0.74 seconds. Assuming this radar actually put out 7 MW, the most likely outcome would be the turkey would explode as an internal moisture pocket flashed to steam.
Microwave Ovens tend to be rated peak input energy, not output energy, and while microwave ovens have efficiencies of 50% to 55% at full load, base on Sailor’s post it is probably much lower for Radar. Assuming Radar systems are rated similar to microwave ovens (big assumtion here) then using the .56 W to 1.5 kW ratio, the turkey would take about 33 minutes.
Both of these numbers assume 100% capture of the radar’s output, which is silly. Even if you built a radar reflective box around end of the tubes you couldn’t expect it to that high, so you would have to downgrade the time based on the percentage of the output energy that actually made it into the turkey.
It also would be unlikely to cook evenly, unless you spun it really fast (assuming a cage type rottisserie thingy to keep it from flying appart as the meat shrunk from the bones).
Stick to popcorn. There is less that can go horribly wrong and when internal moisture flashes to vapor in popcorn it is working. Pop-turkey just wouldn’t have the same appeal, even if they do call them Butterballs.
Engineer Don, I am quite sure the nominal energy of a radar is the peak pulse output energy and you would divide this by the duty cycle to obtain mean output power. A radar transmits for a tiny fraction of the time and listens for more than 99.95% of the time.
I am quite confident there are microwave transmitters putting out much more continous power than any radar possibly could.
People who do not understand the math get hooked up on a big number: wow! a gazillion watts! that’s like all the microwaves in Chicago!
Sailor - sounds right. I kinda figured that ovens would be rated different than Radars, and the 7 MegaWatts continuous output directed as such would be such an excellent weapon that the ranging and detection function would become secondary. I would have heard of them. I only did the calcs 'cause it was a funny question. Also, the waste heat if the Radar was about 50% efficient would create such a heat plume you would cook just being near the damn thing.
The duty cycle explaination fits other known data well.
So, revising the previous calculations and assuming a 0.05% duty cycle, the total cook time would be about 25 minutes. It would still probably hit a moisture pocket in the center and pop. Spinning would help, but getting any sort of even cooking would be nearly impossible. Cooking most meats, and especially nearly whole animals requires time, just to let the heat penetrate and spread out. Try cooking a pound of ground beef in a microwave some time without rotating or flipping. You get dry moistureless bits and red raw bits all over the place, and that stuff is fairly uniform. Nuked turkey would just be bad.
