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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 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.
     
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