Re: Microwave oven leakage test
- From: "M.I.5¾" <no.one@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Fri, 12 May 2006 09:20:46 +0100
"Dr Ivan D. Reid" <Ivan.Reid@xxxxxxxxxxxx> wrote in message
news:slrne61r6e.f03.Ivan.Reid@xxxxxxxxxxxxxxxxxxxx
On Tue, 9 May 2006 15:29:56 +0100, Dave Doubleyew~ <waifs.strays@org>
wrote in <PrKdneTbxZ77Ov3ZnZ2dnUVZ8t2dnZ2d@xxxxxx>:
"Dr Ivan D. Reid" <Ivan.Reid@xxxxxxxxxxxx> wrote in message
news:slrne610lt.7ab.Ivan.Reid@xxxxxxxxxxxxxxxxxxxx
On 9 May 2006 04:10:38 -0700, Norbet <norbet@xxxxxxxxxxxx>
wrote in <1147173038.369329.59040@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>:
Could a small paint chip affect the safe operation of a microwave oven?
No. The paint is only a cosmetic covering over the metal cavity
of the microwave oven. There should be no risk of sparking as the
cavity
walls are nulls in the standing-wave pattern. The only place you should
normally be concerned with leakage of a microwave is at the door seal --
assuming no-one has been silly enough to interfere with the magnetron
feeding the cavity. Dirt on the seal or damage could allow leakage but
given that the wavelength is about (3x10^10/2.45x10^9)=12.2 cm, you need
a fairly large gap to get any significant leakage -- consider the size
of
the holes in the door-screen which allow you to see into the oven but do
not
let any microwaves escape.
Huuummm, interesting, Ivan; is it possible to pad the cavity out so
altering
its resonant frequency, and furthermore is it also possible to give some
idea what kind of modulation transformer would be needed so that one
could
use the oven as a source on 23 cms for EME? ;-}
Well, you're starting to get beyond my area of expertise. As a
licenced ham you're probably better equipped to judge (I was just 2nd
operator on VK0KC in 1980...) I'm not sure it's necessarily a
_resonant_ cavity, but by definition the nulls had better be at the
walls. I assume it's something else that sets the actual 2.45 GHz
operating frequency -- I've had much more experience with thyratrons
than magnetrons. :-0!
The resonant frequency is determined entirely by the geometry of the
resonant cavities cut into the anode block and the way they are strapped
together. Thus it is not possible to alter the frequency of a magnetron
without breaking the device open first. Although it is possible to
amplitude modulate a magnetron by varying the anode voltage, the function is
very non linear and operating range sufficiently narrow for this to be
impractical. Magnetrons were originally used in areas where either
continuous wave operation is required or pulse operation (radar). In
microwave ovens, they are fed from an unfiltered rectified AC supply*, and
as such they only output useable power for a relatively small part of the AC
cycle. The peak power is several times the 650 watts or so average power
that the oven is rated at.
In some very cheap and nasty ovens, they use the rectifying capability of
the magnetron itself, giving a half wave rectified operation. The peak
power has to be higher, but the magnetron's life is substantially shortened.
.
- Prev by Date: Re: Plane hijackers get UK asylum!!!
- Next by Date: Re: Plane hijackers get UK asylum!!!
- Previous by thread: Re: Microwave oven leakage test
- Next by thread: Re: Microwave oven leakage test
- Index(es):
Relevant Pages
|
