Mo' power = Mo' better

Discussion in 'Radio Circuits, Repair & Performance' started by KL7AJ, Mar 10, 2012.

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  1. KL7AJ

    KL7AJ Ham Member QRZ Page

    when it comes to mikeywave ovens

    Our trusty microwave oven died and the wifeypoo boughted a new 900 watt model. The old one was 600 watts. This new one heats up coffee THREE TIMES as fast as the old one, nut a mere 50% faster. There must be something very non-linear in the conversion of R.F. to water molecule excitation. Something else I'll have to look into. :)

    Eric
     
  2. K8ERV

    K8ERV Ham Member QRZ Page

    No, the RATE of heating is linear. But there are different ways of rating power, and different couplings (matching) that can cause varying results.

    There is one non-linearity tho. Cold water absorbs better than hot water, dunno why.

    Early on when actual RF power was measured the Japanese started with cold water and heated briefly so it didn't get too hot. Of
    course they came up with higher ratings than otherwise.

    Now I think most ovens are rated by the line INPUT power which does not always exactly correspond to the output power.

    I am surprised at the very large difference you see tho.

    TOM K8ERV Montrose Colo
     
  3. KL7AJ

    KL7AJ Ham Member QRZ Page

    Could be the older one was just losing power over a long time, and never noticed it! It really was an oldie. :)
     
  4. K8ERV

    K8ERV Ham Member QRZ Page

    Maggys loose power in an odd way. As emission weakens they can "Mode" or jump to a wrong operating point which reduces their output
    power (and increases their internal temp).

    This shift can happen when the match changes, due to the "stirrer" blade position or the food on a turntable rotates to a different position.

    Or the type and amount of food changes.

    My tests show that maggys last a LONG time before failing, but that was 30 years ago and I don't know about present quality.

    NEVER thot I would see a $100 oven!!

    TOM K8ERV Montrose Colo
     
  5. KC9KXW

    KC9KXW Ham Member QRZ Page

    I have a dumb question; what mode does a microwave transmit with to cook food inside or is there no actual mode being used.

    Thanks and 73 Jim
    KC9KXW
     
  6. NI7I

    NI7I Ham Member QRZ Page

    You are forgetting the need factor... The newer ovens have a need sensor.. They can tell when you actually are in need of
    thecaffeinen fix andapplyy bursts of power to speed up the process.. Try the same thing when you are already into your tenth
    cup... OH .. be sure to stand near the oven door so the sensor can pick up a good reading..

    Lee
    NI7I[
    QUOTE=K8ERV;2490146]No, the RATE of heating is linear. But there are different ways of rating power, and different couplings (matching) that can cause varying results.

    There is one non-linearity tho. Cold water absorbs better than hot water, dunno why.

    Early on when actual RF power was measured the Japanese started with cold water and heated briefly so it didn't get too hot. Of
    course they came up with higher ratings than otherwise.

    Now I think most ovens are rated by the line INPUT power which does not always exactly correspond to the output power.

    I am surprised at the very large difference you see tho.

    TOM K8ERV Montrose Colo[/QUOTE]
     
  7. K8ERV

    K8ERV Ham Member QRZ Page

    If you mean the waveguide mode, I don't know the name but think it is the most common, where the 1/2 wave just fits the guide. Some ovens use direct insertion where the maggy antenna sticks right into the cavity or a very small box on the side. I don't know how that works. A maggy has to work over a wide variety of load sizes, locations, dielectrics, etc. I think it is sorta like a ducky, really not matched well to anything.

    Tube insertion/matching is done by heck and by gosh, not theory.

    The mode I am referring to is where the internal vane tips alternate +-+-+-. A bad mode is ++--++-- etc. This is discouraged by "strapping" or connecting each + together by a brazed ring, and each - together to try to force the correct mode. But it is not perfect.

    Trivia. If a guide is too small to propagate the energy at it's freq it is called a "waveguide below cutoff" and the wave won't travel very far. That is why the perf viewing screen doesn't leak (much), the holes are way small compared with a wavelength.

    Back to your regular channel.

    TOM K8ERV Montrose Colo
     
  8. KA9JLM

    KA9JLM Platinum Subscriber QRZ Page

    Not a dumb question at all.

    They operate CW Mode at 2450MHZ. The Frequency that excites water Molecules.

    Amana was the first , and they started at around $1500-2000, They were called a Radar Range.

    Popping Popcorn Voided the warranty, They could not tolerate NO load and the high SWR would damage the tube.

    They have come a long way.
     
  9. K8ERV

    K8ERV Ham Member QRZ Page

    Not so Kemo Sabe. Raytheon invented/first, but it was a huge commercial oven. Licensed the tech to Tappan which introduced the first home oven in the Summer of 1955. It was a large 240v built-in. I joined Tappan in Jan 57.

    Amana did have the first 120v countertop, about 1967.

    TOM K8ERV Montrose Colo

    tpn R4 intro (Large).jpg
    .
     
  10. AF6LJ

    AF6LJ Ham Member QRZ Page

    My grandmother had an Amana in 68 that was amazing back then.
     
  11. K1ZJH

    K1ZJH Ham Member QRZ Page

    The last two microwaves I've owned had labels stating power output. The current 99 dollar Costco special is listed
    at 1100 watts output, 2450 MHz.
    It also works a lot better than the "inverter technology" Panasonic (aka expensive) junker I owned before.

    Pete
     
  12. K8ERV

    K8ERV Ham Member QRZ Page

    Sounds good, but I would like to know how they measure the output power. There are many ways and I don't think there is a
    universal standard. Lotta ways to fudge the test method.

    TOM K8ERV Montrose Colo
     
  13. KK4DKE

    KK4DKE Ham Member QRZ Page

    You drink food and water that comes out of a radioactive machine?
    You do know that if you used microwaved water (cooled) to water plants they will die.
    More 'power' to you brother.
    :confused:
     
  14. K8ERV

    K8ERV Ham Member QRZ Page

    Badly wrong. Microwave energy is NOT radioactive, in any sense. It does NOT change (ionize) atoms, you need photon energy
    that is MUCH higher (ultra-violet) light.

    Please check your facts.

    I have never heard the plant water bit, it is simply not true.

    While I am not quite a plant, I drink oven-heated water/milk for cocoa every morning, and I was 81 several days ago. Maybe in
    better shape than most.

    TOM K8ERV Montrose Colo
     
  15. W9GB

    W9GB Ham Member QRZ Page

    Tom -

    You have already responded to DKE, but the confusion is likely terminology usage and never learning the principles.
    What is Ionizing Radiaition? The consumer/home microwave ovens do not produce it

    BTW, this concept is taught in radio amateur classes in Chicago area (I want to be a Radio Amateur).
    Most health-care workers / EMT tech have already been trained in the concepts.


    IONIZING Radiation
    http://en.wikipedia.org/wiki/Ionizing_radiation
     
  16. AF6LJ

    AF6LJ Ham Member QRZ Page

    The water issue is clouded by the fact that if plastic items are placed in a microwave they can leach chemicals into the water.

    Keep the plastic out of the microwave and all will be well.
     
  17. K8ERV

    K8ERV Ham Member QRZ Page

    Good point (finally---) you can heat things in a microwave oven you would not likely heat otheriwise.

    I doubt if plastic would be a problem if you are heating water as the plastic would not be hotter than the water anyways.

    But something to consider.

    Trivia: At one time some were concerned about food/bacteria on the oven walls. These would not be heated/killed by the RF as
    they would be in a conventional oven. Did not hear anything about this later, doubt if it turned out to be a problem.

    But "verrrrryyy Inereestingggggg"

    TOM K8ERV Montrose Colo
     
  18. KK7EL

    KK7EL Premium Subscriber QRZ Page

    I once owned an Amana microwave. Somewhere in my gray matter I recalled Raytheon owning Amana. Googled it and turns out they bought Amana in 1965.

    Sidenote: When I was wearing a funny green suit every day, I repaired HAWK missile guidance systems and later CW radars, including the illuminator radar that put out about 2500 watts at 10 GHZ. (HAWK missile system was made by Raytheon and was the precursor to the Patriot system now in use.)
     
  19. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Cool on that. I worked on the IHAWK (Improved HAWK missile pgm) as well as Patriot and then AMRAAM pgms at Raytheon...Bedford Labs for development, Andover for production. You might recall if you had a chance to dig into the guts of the illuminator RADAR on HAWK that the rectifier assemblies were potted solid and made by Semtech in California, who was my employer: They were called SA-50s and we used to call them "rectifier compensated capacitor arrays.":p The rectifiers were ten times more reliable than the capacitors used across them, so if anything failed it was always a capacitor.

    I convinced the Army to ditch the capacitors on the Patriot system. It took a lot of talking.
     
  20. KK7EL

    KK7EL Premium Subscriber QRZ Page

    WIK, the recifier assembly was (likely) inside the HVPS -- we called it the "bomb" because that is what it looked like. I tested and repaired probably only 3 or 4 "bombs" total, not a lot of failures, but no recall what components I replaced (this would have been in 1970).

    By chance in your dealings with Raytheon on the aforementioned systems, did you run across Glen Williams (Raytheon Field Eng)?
     
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