Re: TEKTRONIX 491 measuring wifi signals


Chuck Harris
 

When the first commercial microwave ovens were made, they
had simple mechanical timers, and no "heat" settings. The
next generation had simple mechanical timers, and thermal
timers similar to turn signal "clickers" to adjust the on
vs off time. Every enhancement since has been simply
refinements of the same basic formula: Turning mechanical
timers into electronic timers, into microprocessor timers.
Turning mechanical bells into electronic bells. Turning
linear transformers into switching power supplies...

But the basic on/off, "bang-bang" method of controlling the
heat has remained intact: how many seconds on, out of 10
seconds, determines the "heat" from the oven.

Some researchers wanted to take the microwave oven into the
realm of laboratory heating, and found the "bang-bang" style
of heat adjustment way too brutal. For instance, if you
wanted to heat a saline solution in a watch glass, it would
explode around the edges where the water was so very thin,
even though the "heat" was on low... even one second at full
power followed by 9 seconds of being off was too brutal.

So, a colleague of mine developed a precision microwave that
took the duty cycle modulation of the magnetron from seconds
on out of 10 seconds, to power line cycles on out of 10 power
line cycles. And, even balanced the distribution of on
cycles so that if you were at 50%, it was every other cycle
of the 60Hz power, (that may have been my suggestion, I don't
remember anymore) ... Saline in a watch glass was his
standard test.

Heading back to 491's, and wifi signals:

Modern microwave ovens have replaced the heavy, and copper
laden, power transformers with switching power supplies...
which is why they are now available for less than $100.

There is a big cost, however. High voltage capacitors are
still expensive, so the new supplies aren't at all well
filtered, and end up modulating the 2450MHz nominal magnetron
output at the switching supply rate, and the switching
supply rate is not at all stabilized, so it changes with
load. This wreaks havoc with wifi routers which occupy the
same ISM band as do the ovens.... Only the ovens leak way
more power than the routers put out.

A friend once asked me why his "smart" house, and his cordless
phones, stopped working every so often... I asked him if he
had a microwave oven. He said yes. I asked him to notice
if his wife was using the microwave oven when his "smart"
house stopped being so "smart".

You should be able to see this wandering RF noise fest on your
491 whenever the microwave oven is running.

-Chuck Harris
on off timer that im Ford wrote:

I stand corrected (not all that unusual).  Thanks, Chuck.  My guess would be that microwave oven manufacturers either don't know about or don't want to deal with the subtleties of magnetron anode and filament voltages and currents.JimSent from my Verizon, Samsung Galaxy smartphone

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