Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: paul.fr on 07/05/2007 06:46:10
-
If i had the door open, and turned it on. Could it confuse a warplanes "attack radar"
-
George made an excellent reply, unfortunatly i hit the remove button instead of the reply one! I am so sorry George, but knowing how clever you are i reckon you have it backed up. I hope you do! Sorry George [:I]
-
Sorry, if that had been a 60 line response, then I might well have had a backup; but it was only a 6 line response, so it had no backup - I shall try and recover it from my more biological backup system.
Basically, it is extremely unlikely (recklessly so) that an aeroplanes own radar system will be at exactly the same frequency as the magnetron in your microwave cooker. Even if they did happen to be at the same frequency, it is more than probable that it would be able to separate out the continuous wave function of your magnetron from its own pulsed radar signals.
What is more possible (although still somewhat short of probable) is that it would confuse your magnetron signal with an enemy radar that is illuminating it (particularly, I believe some of the early radar guided missiles might have used continuous microwave illumination of its target; but nothing that even approaches any pretence at being a modern radar system should have anything other than a pulsed output, and even the older systems I would doubt would use the same frequency as is allocated for domestic microwave cookers - but then, I suppose one has to also allow for the fact that some crude terrorist device could be built using the magnetron from a domestic microwave cooker to illuminate a target aircraft for missile guidance for a home made missile).
-
Sorry, if that had been a 60 line response, then I might well have had a backup;
ah, no need for you to be sorry George. it was my mistake.
What is more possible (although still somewhat short of probable) is that it would confuse your magnetron signal with an enemy radar that is illuminating it (particularly, I believe some of the early radar guided missiles might have used continuous microwave illumination of its target
Lets say then, during the period when the Russians were fighting in Afghanistan ( i am assuming that at this time the Russians used an older guiding system). Could the Afghanies have line up some microwaves and set them all going to distract the Russian missile from their intended target, say an anti-aircraft battery, giving the Afghanis time to fire off their missiles?
-
Even though the microwave oven signal would be outside the band the radar detectors are looking for it might have enough power to overload the input circuitry of the detector and cause it to fail.
There were stories of people using microwave ovens as decoys to defend radar installations. The incoming missiles targeted the "brightest" microwave signal they could find. An oven with the door removed "looked" like a more important target than the radar transmitter.
I don't know if this was true or just a story. There's one other point I'd make. If the people set their missiles to ignore the 2.4GHz radiation from ovens then the first thing I'd do is build a radar that worked at 2.4GHz.
-
The microwave cooker frequency is carefully secregated from the frequencies used in radar. Airborne radars are frequently mich higher frequency (around 10GHZ or X band)) the sorts of radars that use frequencies closer to the microwabve ovens ( C and S band) are large ground based search radars like those used at airports or on other large ground based and maritime platforms.
-
Yes, you might actually make yourself a target.
There will be some output at 4.8, 7.2 and 9.6 GHz and higher.
-
What is more possible (although still somewhat short of probable) is that it would confuse your magnetron signal with an enemy radar that is illuminating it (particularly, I believe some of the early radar guided missiles might have used continuous microwave illumination of its target; but nothing that even approaches any pretence at being a modern radar system should have anything other than a pulsed output, and even the older systems I would doubt would use the same frequency as is allocated for domestic microwave cookers - but then, I suppose one has to also allow for the fact that some crude terrorist device could be built using the magnetron from a domestic microwave cooker to illuminate a target aircraft for missile guidance for a home made missile).
This is pretty much the case except they're still in service, albeit in the process of being phased out. Semi-active radar air-to-air missiles, such as the AIM-7 Sparrow, are still in use and require the target to be constantly illuminated. These are relatively long range i.e. Beyond Visual Range, or BVR, missiles so the idea is that the target is far enough away to be safely illuminated, either by the launching aircraft or by another targeting aircraft, without putting the aircraft at risk (except from a corresponding BVR missile counter attack).
As I say though, they're being phased out in preference for fully active fire-and-forget missiles that either incorporate active terminal radar tracking (the missile is guided for most of the way by a datalink, either from the launching aircraft or by an AWACS type aircraft), or more recently, passive optical tracking.
While you can establish relative speed using unpulsed microwaves, via doppler, you need to use pulsed signals to establish range, it being derived from the pulse travel time. It's actually the Pulse Repetition Frequency (PRF) that really dictates a radar's range and not so much its power. Each pulse has to be received before the next pulse is sent to ensure you know which pulse you're getting a reflection from, so the longer the distance, the greater the time needed for the round trip, hence the lower the PRF. Many modern military radars now use a technique called frequency hopping, primarily to help get around jamming, where each pulse is sent out at a different frequency and in theory this should enable a higher PRF, as the overlapping pulses could be identified by their frequency, but I don't know if this is actually used.
-
Arise thread...
On a related note, as research for a novel - would it be possible to adapt the magnetron from a microwave oven to serve as the back end for a home-built radar system?
Would it be possible to change the frequency of a microwave oven magnetron?
-
An interesting idea, their use in a Radar system would require them to energised by short pulses typically less than a microsecond I do not know how oven type magnetron's that are designed for CW operation would respond or how stable their output frequency would be.
Re changing frequency, no the frequency is determined by the internal dimension's and is only changed slightly by the operating voltage and the temperature.
The reciever must have some arrangment to follow the rather erratic frequency of the transmitted pulse, easy with computer technology today otherwise it would require an excessive bandwidth giving a reduced S/N ratio.