Microwave Protection

Mickster

Well-Known Member
As an engineer, you have been taught to approach a unknown situation and use reasoning/logic to come to a conclusion based upon sound test methods and evidence provided from those results.

Unfortunately, non-engineers tend to come to their conclusions based upon 'information' from many different angles. Internet user groups, coffee-break discussions, lazy tabloid journalism, woo-woo websites, biased political-pressure organizations, religious brain-washing cults, and many other sources of 'information' on a long list of non-science-based outlets.

Information-overload is in overdrive and the amount of unsubstantiated crap available, to those who don't actually know what they don't know, is frightening. Look at Youtube for instance.

JonSea

Well-Known Member
People who ask honest questions, even (or especially) when they come from a place of little or inaccurate information, should not be ridiculed.

rjenkinsgb

Well-Known Member
I would still like to know if such a gadget can be built that would cancel any such energy around me with out disturbing anything else.
To give you another explanation of why such things are not possible:

Radio waves, whether microwave bands or any other frequencies, are the same "stuff" - electromagnetic energy - as visible light, just different wavelengths (different colours beyond visible, in the simplest terms) and different materials may or may not be transparent or opaque to those "colours".

The general properties and what you can do and cannot do are mostly similar between light and radio waves, especially higher radio frequencies like microwave bands and upwards.

Now try and think of a way _anything_ small could block light getting to you from sources all around you? It's obviously not possible, a small object can only make a small shadow. To completely block light from your body would need a whole-body light-proof suit.

Exactly the same thing applies with any other EM frequency. The only block is a total cage or wrapping of metal or wire mesh.

The most important thing that panic mongering sites and videos do not tell you is that is is power levels which are important. Again, it's like with light.

Sunlight makes you feel warm, as your body is absorbing EM and dissipating it as heat, from the around 1000 Watts per square metre of energy that sunlight contains.
Use a lens or magnifying glass to increase the intensity in a small area and you can burn things with it.

A normal room filament light bulb typically emits around 100W of EM energy as visible light and infrared (radiant heat).

The intensity is far too low at a normal distance to feel any warmth from it - but it's still far, far stronger and having more effect on your body than any type of EM emission from any consumer gadget that uses radio frequencies.

That EM meter your friend has may well be a highly amplified device sold by some scammers to convince people there is "dangerous radiation" so they can sell them protection gizmos that do absolutely nothing.

Such a device could easily have been picking up WiFi signals from something nearby or in another building.

Saying signals of that incredibly low intensity are dangerous is like saying all flashlights should be banned because they use light - and you can burn things with "just light", using sunlight and a lens to "prove" how harmful light is!

It's not what, it's how much!

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unclejed613

Well-Known Member
The waiter said it was a professional combination rf ef emf meter as he does home wiring on the side.
i have used a real microwave leakage tester. if everything is properly assembled, the leakage from the cavity, waveguide section and magnetron are only detectable with the top cover removed, and even then it's well below safety limits. the only time i have ever seen measurable leakage from an oven was one where the cavity (the oven itself) had been visibly deformed from the unit being dropped. your co-worker's "EMF" meter is just picking up magnetic noise from the AC power lines, and not RF, and certainly not 2.4Ghz leakage from the oven (which actually requires very low capacitance diodes to measure). a real microwave oven leakage tester has a very distinctive cone-shaped pickup and the purpose of the cone shape is to get the antenna the proper distance and orientation from the surfaces and seams being tested.

Nigel Goodwin

Super Moderator
i have used a real microwave leakage tester. if everything is properly assembled, the leakage from the cavity, waveguide section and magnetron are only detectable with the top cover removed, and even then it's well below safety limits.
I would disagree, having spent decades repairing and servicing them I've tested many hundreds - and while it's fairly pointless testing with the top off, I've done that (as a matter of curiosity - as you do) a number of times, and never found any detectable leakage even with the top off.

The dangers of microwave ovens isn't any imaginary leakage, it's the seriously high voltages and current that are exposed with the top removed - which WILL kill you.

As a registered microwave service agent we weren't allowed to sell any parts to people that required removal of the top - so no fuses, no oven lamps (unless there was a little 'door' for changing the lamp), but we could sell waveguide covers which are accessed from the cavity.

unclejed613

Well-Known Member
Mr Cat says "once i get this off my head, i will shred my owner......" i have rarely seen a cat look so sullen...

Mickster

Well-Known Member
Mr Cat says "once i get this off my head, i will shred my owner......" i have rarely seen a cat look so sullen...
Do any of the cats-with-hats look happy?

Stupid owners.

ronsimpson

Well-Known Member
Do any of the cats-with-hats look happy?
I tried to find a picture of a cat warring a colander, but that seemed too political. Tinfoil hat seemed to state what I was thinking.

Picture of a cat full of meat balls. He did not touch the pasta.

Nigel Goodwin

Super Moderator
Do any of the cats-with-hats look happy?

Stupid owners.
I have cats, two of them currently, it would be folly to try and make them wear a hat.

One of our previous cats, Cleo, had the sharpest claws you've ever seen on a cat - and she wasn't afraid to use them!

unclejed613

Well-Known Member
when i was a kid, i found two things that made the cat act weird... so weird in fact that one would be almost certain to die laughing....
1) scotch tape around the paws made the cat do a crazy dance...
2) use scotch tape to tape the whiskers back made the cat walk backwards...

after those adventures the cat would hide upon hearing somebody using scotch tape

gophert

Well-Known Member
when i was a kid, i found two things that made the cat act weird... so weird in fact that one would be almost certain to die laughing....
1) scotch tape around the paws made the cat do a crazy dance...
2) use scotch tape to tape the whiskers back made the cat walk backwards...

after those adventures the cat would hide upon hearing somebody using scotch tape
I had seen cat whiskers taped together (bundled in front) and that poor cat didn't know what to do - it was paralyzed.

be80be

Well-Known Member
If I was betting the thing was reading the lights or motor.
If a microwave leaked much we all be cooked by now LOL

Here a pic of a real tester tho

Mickster

Well-Known Member
As a child, we had a cat (female) as a pet. Apart from when it came to feeding time, she never wanted anything to do with my sister or my mother.
She came to me for attention and was fine with any form of stroking, but not belly-rubs. If I attempted to rub her belly, she would jump up and bat both sides of my head with her paws, but never with the claws extended.

Granny also had a cat which was particularly greedy and got to around 17 pounds. She would climb on the back of a chair and open the latch on the pantry door, in order to get into the sugar bowl. Any un-attended coffee cup was fair game and she went crazy for rice pudding when it was around. She did not like to be brushed and had very thick fur - in order to be able to brush her, she had to be drugged and the only way to get her drugged was to wrap the pill in some cheese......anything else would result in her spitting the pill out.

DrG

Active Member
And they say Electrotech is hostile towards new users. How do people get such wacky ideas?

Oh yeah, they read posts like this one. Frank asked a reasonable question; a question in an effort to learn something. This was an opportunity to educate and share information, and possibly get someone interested in electronics.

Instead of taking the opportunity to explain that:

A: There is no magic "personal shield" he can wear.

B. That the measurements are very suspect and probably wrong.

I know in your combined thousands of years of experience, you-all personally have never seen a leaking microwave, you DO NOT know the condition of the microwaves in this kitchen. Equipment in many restaurants lives a hard life, and you don't know who might have "fixed" these microwaves in the past.

Instead, you guys have all ridiculed the original poster and provided him approximately ZERO information.

Good show guys.
You have a point, but I am now considering that it could be trolling as has already been stated. How can one tell the difference?

When I saw the post on another board, I answered in a reasonable and respectful manner and was thinking along the lines that you said. I provided links to the electromagnetic spectrum and for microwaves. I queried what the device was and indicated suspicion that it was not measuring what the user thought that it was measuring. I indicated a candid but skeptical evaluation of the idea that they could be emitting MWs when not on.

This (my post) was after an educated and experienced user wrote intelligently (and possibly too technically) about the safety efforts in microwave ovens. Subsequently there were a few "tin foil" posts.

The OP came back and said that he learned about the spectrum and asked how he could build an RF "jammer" that would block the MWs. A moderator then locked the thread...and then it was re-opened for "non-jamming" discussion.

I just can't tell about the trolling. If it is/was, mission accomplished, but it is not much of an accomplishment.

AnalogKid

Well-Known Member
Some things ...

All electrical and electronic devices leak electromagnetic fields. All. A.L.L. A*L*L. Every single one. ALL of them. From Flashlights to F-15 targeting radars, ALL electric / electronic devices produce some amount of electromagnetic radiation that is not useful / unwanted / unintended / etc. ALL.

That being said, the issue is whether or not the radiation is greater than or less than some determined safe value. The debate about whether or not the safety levels are realistic is completely separate from how to apply the findings. What is undisputed is that there is a cumulative effect. The errant field of one oven might be completely safe, but 10 of them in the same room could be *way* beyond the intent of the testing. The question has merit, but the advice he has received so far has the appearance of value while actually creating unnecessary concern with false data.

Determining the radiated field strength of a microwave oven is not a simple task, not nearly as simple as pointing a field strength meter (of any kind) at it. Devices are placed inside a shielded room or cage (sometimes called an anechoic chamber, although that is only one of its required properties). A high-gain antenna is pointed at the device, and a receiver and spectrum analyzer show the field strength at whatever the frequencies of interest are. The test is repeated for each of the six sides, and development testing includes focusing on the hinges, door seals, and the screen in the front door. Yes, the screen leaks a little bit; ALL shields leak (see above), which is why it is so carefully designed and verified.

The hard part about testing is making sure you are measuring *only* the device, and not the building security system or wifi (which almost certainly are in the same frequency band). This is why amateur on-site testing is (almost) by definition of low or no value.

ak

Nigel Goodwin

Super Moderator
Determining the radiated field strength of a microwave oven is not a simple task, not nearly as simple as pointing a field strength meter (of any kind) at it. Devices are placed inside a shielded room or cage (sometimes called an anechoic chamber, although that is only one of its required properties). A high-gain antenna is pointed at the device, and a receiver and spectrum analyzer show the field strength at whatever the frequencies of interest are. The test is repeated for each of the six sides, and development testing includes focusing on the hinges, door seals, and the screen in the front door. Yes, the screen leaks a little bit; ALL shields leak (see above), which is why it is so carefully designed and verified.
I seriously doubt such tests are ever carried out these days, and haven't been for decades (if at all?) - the incredibly low prices and tiny profit margins mean it's not viable to carry out such pointless tests, it's a very old and well understood piece of technology.

But in any case, the entire thread has NOTHING to do with any imaginary leakage from Microwave ovens, as the toy meter (whatever it may have been?) provided readings even when no ovens were in use.

AnalogKid

Well-Known Member
First, the leakage is not imaginary. By definition it is real. And the health hazards of both ionizing and non-ionizing radiation are very real, and lethal at high enough levels.
I seriously doubt such tests are ever carried out these days, and haven't been for decades (if at all?) - the incredibly low prices and tiny profit margins mean it's not viable to carry out such pointless tests, it's a very old and well understood piece of technology.
In order:
In the US, for decades, anything for sale that has internal frequencies at or above 10 kHz must be type accepted (or whatever the current term is) by the FCC. For many products there are two applicable emission level profiles, Class A and Class B. B is harder than A to meet, but not as tough as MIL-STD 461, which is not as tough as TEMPEST.
The tests are not pointless. Every year products are rejected because of radio interference with other devices (a solid state light ballast jamming an FM radio receiver) and hazardous emissions levels. Back in the 80's, Radio Shack had to eat thousands of PCs because they went to manufacturing before testing was complete, and the model failed. Of course, companies do not brag about this in their advertising. "Hey, buy our new oven! It took us only 5 tries to get the RF leakage down below 'death ray' levels!" That doesn't mean it doesn't happen.

Seriously ?!?!? I really don't want to pick a fight with a mod, but that's like saying it doesn't need to be safety-certified because AC power is old and well understood.

A microwave oven is an unlicensed 1 kW 2.4 GHz radio transmitter. As dozens of YouTube videos show, that is a dangerous and lethal amount of energy. My basement bar one (GE) cost $79 in 2004, and has an FCC ID number right below the UL Listed ID. So does the brand new one in the remodeled kitchen. So does a$5 LED bulb for a desk lamp. The cost of an item is not an exemption; if anything, it is a red flag.

ak

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