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Microwave cooker modulation

Discussion in 'Radio and Communications' started by Mosaic, Jul 12, 2017.

  1. Mosaic

    Mosaic Well-Known Member

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    I understand that microwave appliances operate at near Wi Fi frequencies.
    Is it possible to modulate a microwave appliance to transmit a wifi signal?
    Setting aside FCC regs etc. I am wondering what it would take to be done.
     
  2. crutschow

    crutschow Well-Known Member Most Helpful Member

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    No.
    The magnetrons in a microwave oven operate at a fixed frequency as determined by their internal dimensions.
    That's why they are used in fixed frequency applications like ovens and radar.
    And I wouldn't worry about FCC regs., I'd worry about frying your eyeball. :eek:
     
  3. Ramussons

    Ramussons Member

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    And they are not "continuous" like oscillators. They operate in pulses.
     
  4. dave

    Dave New Member

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  5. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I don't think so, the 'pulsing' is simply used to lower the power level, on full power it's a continuous oscillation.

    However, they would be completely unsuitable for WiFi.
     
    • Agree Agree x 1
  6. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    I supposed you could amplitude modulate it, for what that is worth but frequency probably does not vary that much. If you vary the input power the output power varies too unless you fund across one that has some sort of internal regulator but none of mine did in the past. When the input voltage goes down, the power goes down a lot. For here, 120vac is the norm but lower that to 100vac and there is a BIG difference in the cooking power.
    The one i have now though has an 'inverter' inside so the output is always continuous even on most lower powers, until it does down to power level '2' and then it starts pulsing on the lowest continuous power setting which is '3'.
    I have not tried to vary the input to this new one yet though. It's a Panasonic "Inverter" microwave oven.
    Dont like the power setting method though where you have to hit the power button 7 times to get to power level 3.
     
  7. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    That's because the heater voltage goes down accordingly, so the magnetron doesn't run properly.

    As for 'inverter' ovens - they are light to carry, and that's the only advantage.

    Repair wise they are a complete disaster, every one is scrap if it goes faulty. The normal failure in them is the magnetron, but in every case I've seen it takes the PSU with it - and while the mag is expensive, the PSU is really expensive.
     
  8. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi there,

    Oh is that what causes the main power drop? That's interesting. So what happens is the food cooks slower as if it had less power to begin with.

    You mean less weight so when you lift it it is easier to lift and carry to a new location? What makes it lighter?
    I find that the lower powers cook meats less intensely and so the meat is more tender when it's done. Takes longer to cook though.
    The pulsing power ovens always cook with maximum intensity so the meat comes out tougher.

    I havent had to repair one yet but noticed they dont give an option to turn off the beeping so it requires internal modification to get it quiet.
     
  9. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Yes, what makes it lighter is removing the massive (and heavy) mains transformer, and replacing it with a SMPSU.

    The mains transformers were seriously reliable, the SMPSU's die at the slightest provocation :D

    I don't recall any microwave ovens having that option?.
     
  10. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi again,

    Oh yeah, i didnt realize that they removed the transformer because they where using use a switcher. I just didnt think of it until you mentioned it now, very interesting. I guess if this dies then it will be the first mic oven that i was not able to salvage a line transformer from then, boo hoo :)

    Yeah i an hoping it lasts as it was more expensive than my last 100 microwaves (ok just three i think before this one)

    Two of mine had a button sequence to turn off the beeping. One (really old one) was an Emerson, the other was a Sharp. Both long gone now.
    In case you want to look for one, you can find out in the manual as i am sure you know, and sometimes they post the manual on line somewhere so you can find it and look in the manual to find the button sequence. It's been a long while now but the Sharp had some button sequence and i had to hold one button in for a few seconds if i remember right. If the house 120ac power went out though i had to do the sequence all over again when it came back on.
    I would bet that you just never had to do that, that's all. The beeping bugs me so i like to turn it off or defeat it some other way.
     
  11. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    It's a more expensive way to make a PSU.

    Mine 'dings' - it's an old Toshiba, and has a mechanical digital clock - so no beeping noises :D
     
  12. crutschow

    crutschow Well-Known Member Most Helpful Member

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    You mean with the flipping digits like the old digital alarm clocks? o_O
     
  13. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    No, it consists of rotary 'wheels', with the numbers on the edges.
     
  14. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Wow havent seen an oven like that in a long time now. I suspect it is low power?
    Easy to set though, i like that :)
     
  15. davenn

    davenn Active Member

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    as Nigel Goodwin said, that is incorrect



    it has been done and varies well enough for ATV which is reasonably wideband ...
    I do have the paperwork for a project presented in 73 Amateur Radio mag of some years back, that an amateur radio op used for doing ATV on 2.4GHz using around 500W microwave magnetron


    Dave
     
  16. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    It's 650W, as were all ovens of that time (about 35 years ago) - I'm fairly dubious about the claims of modern ovens, I suspect mostly the increased power (800 or 900W) is imaginary, and obtained by a different method of measurement.
     
  17. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Sounds cool.
     
  18. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi Nigel,

    If you like we can do a little test. If you measure the input current to your microwave oven on the highest power setting we can compare notes, and if you would also like to measure input power maybe we can do that too, although i think input current would be enough in this case and my watt meter only goes up to 15 amps and the microwave i have takes maybe around 16 amps at the highest setting.

    The oven i have now is rated for 1200 watts cooking power and i estimate the input current at around 16 amps. I never use it at that power though i always set it much lower because the line cant really take 16 amps here as there are other things plugged in and in the summer months the line voltage gets pulled down quite a bit too so i wont get full voltage anyway.

    We can also do a quick boil time test. Using a styrofoam cup and exactly 8 ounces of room temperature water (say 80 degrees F) and start the oven and see how long it takes to start a violent boil. The cooking power (for that shape and quantity and substance and position in the oven) is determined from that time measurement. Of course the position affects it too though, as mine boils fastest when i put the cup near the outside diameter of the circular plate that rotates. You could try that and another test in the center of the cavity.

    The most revealing will be the input current, but the cooking power test with the water will reveal a rough efficiency too which we might have to compare also.

    So if you would like to compare, at least measure the input current.
     
  19. Mosaic

    Mosaic Well-Known Member

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    Calorimetry is a precison means for RF power metrology.

    Looks like PWM is the only way to use those hundreds of watts of WiFi power to move data, sorta like a digital CW. Wonder if I can build a wave guide to channel that power into a dish. Hope I don't make the news, man cooks himself for dinner!:eek:

    Then, again a high gain pulsed dish will probably cook any birds/bats/bees/bugs flying by. Maybe generally a bad idea. :nailbiting:

    Wonder if it will take down an amazon drone?
    Hmm, it will make a remarkable defense against home intruders. Ghostbusters come to mind.

    In terms of a real use....it will selectively melt all the snow on your property so you don't have to shovel.

    That sounds like the old electronic mags adverts... Military Beam Weapon ---DIY.
     
    Last edited: Jul 29, 2017
  20. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Hi,

    Sorry for the delayed reply :D

    You don't get domestic ovens that powerful over here, and commercial ones are simply two domestic ovens in one box - so two magnetrons (and everything else) for double the power, with a single control system.

    Obviously over here we can get over 3000W from a standard mains socket, so we aren't as power limited.

    Power testing is simple, and is commonly done as part of the servicing procedure - this site explains how to do it.

    http://www.celtek-electronics.com/microwave-leakage/microwave-oven-power-test
     
  21. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi again,

    No problem.

    That's interesting that the oven powers are limited over there. I have to wonder why that is so.

    Yes we only have 120vac here so it's not as good. I wish that they started using 230vac long ago. Looks like we are stuck with it.

    The power test i use is similar except i dont use any thermometers except for the usually one to get the water temperature from the room temperature. I then assume when it starts to boil it's at 212F.
     

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