HERF Gun Zaps More Than Your Dinner

Instructables user [Jimmy Neutron] had an old microwave sitting around and figured he might as well gut it to build a high-energy radio frequency (HERF) gun.

The concept of a HERF gun is not incredibly complex. Much like your microwave at home functions, a high voltage power source is used to drive a magnetron, which produces micro wave radiation at 2.45GHz. These waves are then guided away from the magnetron using a waveguide, towards whatever the target might be. These waves then energize the target in a similar fashion as the water molecules in your food are energized during cooking.

[Jimmy] has not quite finished his HERF gun as he still needs to build a waveguide for it and then safely mount it for use. In the meantime, check out the pair of HERF guns we found in the videos below.

As a parting note, we must stress that building a similar device is dangerous, very dangerous – especially if you do not know what you are doing. Microwaves contain high voltage components, and exposure to microwave radiation can be deadly under certain circumstances. Stay safe!

Looking for more microwave fun? Check these out!

76 thoughts on “HERF Gun Zaps More Than Your Dinner

  1. Wow its like the new age hillbillies thow it together and see what happens it’s for of a hack to see show how dum ppl. Can be I think I will turn it off it’s starting to tingle ??? if it tingels I thinks u have a design flaw back to the drawing bord

  2. This qualifies as a hack? When I was a kid we took a lamp cord, stripped the ends, and touched it to metal stuff to watch things explode. Post that.

    And a few people have mentioned it, but your retinas are the most prone to damage, as they are not cooled by as many blood vessels as other parts of your body. So you can still have kids, you just won’t be able to see them.

  3. Legal schmegal – even if it may be illegal it is illegal only when you get caught. Let’s look at the numbers.

    Let’s assume the magnetron radiates 800 watts in an omnidirectional way as a point source. (I know, I know, “let’s assume a spherical horse”.) Let’s assume the harmless power density for nonpermanent exposure is 5 mW/cm2 (allowed mw oven leakage is 5 mW/cm2 at 5 cm from the surface).

    The actual safe power densities for short-term exposure can be pretty higher. Tissue damage occurs at 42 ‘C, penetration depth for 2.45 GHz where half the energy is absorbed is about 2 cm, we can approximate the heat capacity of tissue to be equal to water (4.2 J/gK); let’s assume 30 second exposition, 100% absorption in first centimeter of the tissue, no heat losses. Heating a cubic centimeter of water by 5 degrees requires 21 joules. To heat a 1 cm layer of water by 5 degrees over 30 seconds takes 700 mW/cm2. For 10 seconds it is 2.1 W/cm2, for 2 seconds it is 10 W/cm2.

    (The actual absorption in the tissue depends on the tissue character. Fatty tissues will absorb less energy than water-rich ones (e.g. muscles). The heat capacity of tissue is lower than of water, but in reality there will be heat losses to the surrounding environment and to deeper tissue levels.)

    The surface of the sphere is calculated as 4*pi*r^2.

    At 10 cm distance the power density is 630 mW/cm2.
    At 25 cm it is 100 mW/cm2.
    At 50 cm it is 25 mW/cm2.
    At 75 cm it is 11 mW/cm2.
    At 100 cm it is 6.3 mW/cm2.
    At 115 cm we are at 4.8 mW/cm2, below the power leakage limits considered safe by cover-your-ass govt standardization body.
    At 253 cm we are at 1 mW/cm2, a level considered safe.

    This however assumes homogeneous field and no reflections. (In the oven cavity the radiation is reflected from its walls so the power is not lost so easily.) Also any sort of an antenna will focus the beam and lower the amount of losses in that direction (and increase it in others, according to the antenna’s pattern). Conductive objects can also transfer the energy along with little losses and reradiate it or couple it to other objects. So there are caveats for the actual experimental setup.

    I’d say that the actual danger is in the very vicinity of the magnetron and, more than that, in the high voltage capacitor. (BEWARE of that one, it packs a nasty punch.)

    Somebody please validate my calculations, as they are just an irritated back-of-the-envelope scribbling. However at the first glance it does not seem that, while not entirely safe, the danger of such experiments is somewhat below the sky-is-falling level of the local Wussy Brigade noisemakers.

  4. Last sentence corrected:
    However at the first glance it seems that, while not entirely safe, the danger of such experiments is somewhat below the sky-is-falling level of the local Wussy Brigade noisemakers.

    Also, I’d say this may count as an initial stage of a more advanced project. Give the guy a break and some time.

    For the beginning, what about using a thermochromic paint (or the liquid crystal sheet) on a wetted rag to visualize radiation pattern of various antennas?

  5. I’ll like to point the difficulty of tuning an antenna at this freq. It’s not as simple as making a wifi antenna. In wifi the power reflected by the SWR does not breake your transmitter because of the little power used. But with high power the heat will probably toast your transmitter in a matter of seconds.

  6. Constructing a projected microwave energy device will soon be very popular as one of these when projected against a survelance drone, such as the Draganflyer X8 used by police departments, will scramble the CPU controlling the same and send it crashing to the ground.

  7. Just for You all to known. Microwaves heat up the water in food. 80% of brains is water, so permanent brain damage may occur without proper shielding. Also I know guy, who used to use his microwave oven without door (He blocked the safety mechanism). Microwaves cooked bone marrow from his fingers and those had to amputate.

  8. I don’t think HERF guns are bad…neither are coil guns. The problem is too many people who don’t understand what they are doing. You really need to use the waveguide, otherwise you are playing with fire. I’m interested in mounting one on the end of a satellite dish with the wave guide. It’s the only effective way I can see to narrowing the waves to a focused point, rather then radiating everywhere. There should also be a substantial gain. This should focus the waveguide along with increasing the wattage. The amount of leakage is questionable. This is similar to what the military does on some of there so called weapons mounted on vehicles (like ADS).

    I became more interested in these weapons, along with non-lethal ultrasonic weapons due to some neighbors using electronic harassment on me and discovering that the police have been less then useful. Non-lethal weapons fall into the grey area of the law, so the police wont do anything and neither will the courts. There isn’t any bodily harm and even if there is, proving it is a whole different story. Calling the police either angers the neighbor(s), so they use them more or they get a thrill out of it and still use them more. The end result is either move away or fight back using similar tools. The problem is too many idiots that have know clue of what they’re doing and thats what scares me. Think if a total buffoon got a hold of a well made HERF and used it on people they didn’t like. Scary thought. Much like the same person having a gun.

  9. Hack *3, modify an off the shelf minature 22 GHz Gunnplexer (4 of them!) so they are phase locked together.
    9mW at 22 GHz multiplied by a factor of taking out all the attenuators and replacing the diode(s) with slightly larger but still somewhat compatible ones modulated with the CPU base clock of the machine under attack.
    Very effective on: laptops, annoying SO’s portable DVD player, external hard drives etc. Not so good on other systems but it has applications such as EMC testing so technically its OK to build if used in a secure environment :-)

    Added advantage here is that its designed not to be a hazard to anything living as it has an “idiot sensor” so that if you do point it at anything hotter than a typical laptop it refuses to work.
    The same method can be used for making HTSCs at home as an alternative to more dangerous methods like using an actual microwave oven.

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