OT: uneven cooking in microwaves

[rbowman]

Do not attempt to microwave raw chicken livers...

[Mark Lloyd]

[snip]

I see some things here with fused plugs, mainly miniature holiday lights with 3A fuses.

[snip]

During a long power outage, when I needed to run my garbage disposal. I was probably too careful, first making no one else was inside and locking the doors, then turning off all breakers, finally putting the ends on the cord. Afterward, undoing all that in reverse order.

[snip]

[Mark Lloyd]

I've wanted to do that since 1988, when there weren't any PVRs. Once I got one (ReplayTV 2020) in 1999, I found I preferred to have it record things automatically.

BTW, I still have that 2020, although it is almost useless now since cable went to all-digital and all-encrypted, and that unit won't control modern cable boxes.

[jrwalliker]

which makes it practically usless for anything out doors and perfect for cooking food

The main reason I mentioned it was that TNP thought it was important when he wrote: Actually there is something specail. It is heavily absorbed by water which makes it practically usless for anything out doors and perfect for cooking food

Anyway its good to get this out of the way. Water vapour in the atmosphere does not significantly absorb microwave signals in the

2.4 to 2.5GHz band. There is no water molecule resonance in that range. Lots of people think there is, but the evidence against it is very clear.

You snipped the rest of what I posted, showing that there is nothing special about 2.4 to 2.5GHz in liquid water or saline. Frequencies hundreds of MHz higher or hundreds of MHz lower would work perfectly well. There is a trade-off between penetration depth which increases with decreasing frequency and the cost of the magnetron which gets more expensive at lower frequencies because it needs a larger copper block and a larger magnet system. The overall product size would also be larger at lower frequencies (although recently developed high-power RF transistors may dramatically change this).

The original developers of microwave ovens were also probably motivated by the ready availability of S-band radar magnetrons which had been manufactured in large quantities towards the end of WW2.

The selection of the 2.4 to 2.5Ghz band was not necessarily optimal for cooking food but was part of a set of engineering compromises.

Once the band had been enshrined in international standards, and other nearby frequencies allocated for other purposes it would have become impossible to change.

However, another frequency which is widely used for microwave cooking of food and for which there is a frequency allocation is 915MHz. The higher cost of the equipment at this frequency means that it is almost exclusively used in industrial ovens.

Have a look at table 3 which lists penetration depths for different kinds of food at 915MHz and 2.45GHz.

There really is nothing special about 2.45GHz apart from regulatory standards and engineering tradeoffs.

John

[ZakJames]

That?s bullshit. I share my wifi with my back neighbour and plenty use wifi outdoors.

Because of the absorption peak at frequency.

Because the atmosphere has nothing to do with FOOD.

Repeating that claim changes nothing.

[jrwalliker]

I completely agree with you. I was not the one who claimed that. Atmospheric attenuation at 2.45GHz is negligible.

There is no absorption peak at 2.45GHz either in water vapour or in liquid water or in salt solutions. Food is going to be variable because there are so many different kinds of food, so water is used for the regulatory testing of microwave ovens, even though it does not have an absorption peak at 2.45GHz.

No, repeating it changes nothing. Nor does snipping all the evidence that contradicts your position make that position true.

I have quoted data that relates to the behaviour of water, salt solutions and food.

Let me requote the one about food that gives data on relative penetration depths at 915MHz versus 2.45GHz for a variety of FOODS.

table 3

There are commercial microwave ovens that operate at 915MHz, although they are only used in the USA and not Europe for regulatory reasons. They give better penetration into the food than

2.45GHz ovens, but are larger and more expensive.

John

[ZakJames]

Wrong and food isnt just water either.

But food is mostly just a few things that absorb RF.

Irrelevant to what gets heated by the microwaves in a microwave.

Yes food does.

What I snipped had nothing to do with FOOD which is why it was removed.

In the atmosphere, and so not relevant to the heating of food in a microwave.

That?s a lie.

That says nothing about whether there is an absorption PEAK at 2,45 MHz.

[jrwalliker]

It would be odd for manufacturers and regulators to agree on testing with water if it is not relevant to normal use. In any case, many people do heat water (often in the form of drinks, soup etc.) in microwave ovens.

What evidence do you have to show that "food" has an absorption peak at 2.45GHz? It would help if you could specify which food you are thinking of, as there are so many different kinds and they can't all be the same.

I gave you this link earlier. It does report on salt solutions and water, so there is no lie:

I didn't claim that it did. However, it shows that some commercial microwave ovens operate at 915MHz and gives comparative data in relation to penetration depths. This clearly demonstrates that microwave ovens can work well at frequencies other than 2.45GHz.

Do you have any data to support your assertion that there is an absorption peak at 2.45GHz in water or in "food"?

John

[ZakJames]

Its useful for TESTING but that?s irrelevant to what is being discussed, whether there is an absorption band at 2.45GHz with FOOD.

Duh,

If this is the best you can manage, here goes the chain on your even more irrelevant shit.

[spuorgelgoog]

915MHz industrial ovens are permitted in the UK with a higher 'interference' output level compared to the EU, which is why the UK is a popular location for such industrial processes.

Owain

[tabbypurr]

There's no point arguing with Rod Speed the troll, aka zak james & many many other aliases.

NT

[Commander Kinsey]

So is that why Wifi is so shit? It hardly travels very far at all until it starts dropping out. Presumably some moisture in the air kills it too. Someone wasn't thinking when they chose that frequency.

[Commander Kinsey]

What is reverse baked? Frozen?

[Commander Kinsey]

It's true that if you stand in front of a Wifi router, the person sat behind you loses signal.

[Commander Kinsey]

Grow and cook the vegetable in one easy process!

Only if you leave the door open while cooking.

Not in a frozen lump of veg. Loads of ice everywhere. Anyway, I told you the problem was frozen bits were left. As in ice. That should have absorbed.

[Commander Kinsey]

I just checked argos.co.uk and they sell them from £60 to £600.

Why pay more for something you use less often? And to me, a washing machine shouldn't cost more, it's just a motor. A microwave has that magic thing in it!

I never buy a new washing machine, or a new car, both are way overpriced.

[Mark]

I wonder how many they actually sell at £600. I would guess not many.

As I said a malfunctioning washing machine can flood the house.

Oh. It's bit more than just a motor. They would usually have different programmes for different fabric types. One size doesn't fit all. ;-)

I also have never bought a brand new car. I would agree that they are way overpriced. But I wouldn't buy a used washing machine. Why would anyone sell one unless there was something wrong with it?

[Mark]

Isn't this a spork? ;-)

[tabbypurr]

People moving in together don't need 2 machines. Moving somewhere that already has a machine. People buy new appliances for all sorts of silly reasons. Owner died, went into care, going to jail etc. There are many good used machines available, and many not ok but easily fixed.

NT

[Steve Walker]

We have a pair of microwaves that were around £300 each. The reason being that they are more than just microwaves, they are also conventional ovens and grills and are large sized (you can fit a turkey in).

One mainly gets used as a conventional oven and the other as a microwave, but we do use the flexibility of having two conventional ovens or, less commonly, two microwaves at times.

Our dishwasher was second-hand. A £400 machine for £100 at only 8 months old. The owners had just moved house and were putting in new kitchen, with integrated machines.

SteveW