Microwave cooker modulation

Nigel Goodwin · Jul 30, 2017

MrAl said:
Hi again,

No problem.

That's interesting that the oven powers are limited over there. I have to wonder why that is so.

That's the power that standard magnetrons provide - as I said I've never heard of higher power ones - possibly yours is quoting the power consumed from the mains, rather than the actual RF output?.

Yes we only have 120vac here so it's not as good. I wish that they started using 230vac long ago. Looks like we are stuck with it.

We're actually 240V in the UK, the 230V rating (for the EU) is for equipment specifications and must cover the UK's 240V and the rest who are 220V.

flatfootskier · Jul 30, 2017

I'd bet many ovens have lousy efficiency - magnetron losses can be very significant.

MrAl · Jul 30, 2017

Nigel Goodwin said:
That's the power that standard magnetrons provide - as I said I've never heard of higher power ones - possibly yours is quoting the power consumed from the mains, rather than the actual RF output?.

We're actually 240V in the UK, the 230V rating (for the EU) is for equipment specifications and must cover the UK's 240V and the rest who are 220V.

Hi,

Well the input current is over 15 amps i think it's 16 amps, and 16 times 120 is 1920 watts input power. With 1200 watts cooking power that is about 62.5 percent efficient which is about right. My older oven only drew much less current on high from the wall and that was known to be a lower power unit. When i turn this new oven down to power level 3, it draws around 6 amps from the wall, so i know it has to be lot higher power than the old oven.
How they do this i dont know, but i never heard of a limit on the power of a magnetron, that they could never design one over 700 watts or something like that. I might note that i read about them being able to get much higher. I dont think they are using two in this oven, but i'd have to take it apart to find out for sure.
I also did a test when i first got the oven and it boiled 8 oz of water in something like a minute or a minute and a half, which is quite fast. Cant remember the exact time now though.

flatfootskier · Jul 30, 2017

I've never known a microwave to regulate power other than by adjusting its duty cycle - seconds per burst, rather than bursts per second.

Nigel Goodwin · Jul 30, 2017

MrAl said:
How they do this i dont know, but i never heard of a limit on the power of a magnetron, that they could never design one over 700 watts or something like that.

I'm certain you can buy magnetrons FAR higher than the standard ones used in ovens, after all they were invented for radar applications.

As I mentioned previously, all the commercial ovens I've repaired simply used two magnetrons to give double the power though, and didn't use any 'unusual' magnetrons.

MrAl · Jul 30, 2017

flatfootskier said:
I've never known a microwave to regulate power other than by adjusting its duty cycle - seconds per burst, rather than bursts per second.

Hi,

Most of them do that, but then Panasonic came out with their line of "inverter ovens" that use a inverter to regulate the power in a way that does not need pulsing. This means the actual power level goes down so the input current geos down too. Not just the average current, but the instantaneous current goes down so it gives a continuous cooking power rather then a pulsing cooking power.
If you measure the input power to a regular oven it will go from every low to very high, then back to very low, then back to very high, etc., on the lower cooking levels. That way it obtains an average cooking power that is less than full power.

davenn · Jul 30, 2017

Mosaic said:
Wonder if I can build a wave guide to channel that power into a dish.

good grief, why do you need a dish, is 500 - 600W not enough ??

Nigel Goodwin · Jul 31, 2017

davenn said:
good grief, why do you need a dish, is 500 - 600W not enough ??

To match the output of the magnetron, the cavity of the oven is designed to give such a match.

Like any transmitter you can't just use it without an aerial, it will destroy the transmitter - and not work well either.

flatfootskier · Jul 31, 2017

davenn said:
good grief, why do you need a dish, is 500 - 600W not enough ??

I can think of 500-600 reasons why this is a bad idea...

davenn · Aug 3, 2017

Nigel Goodwin said:
To match the output of the magnetron, the cavity of the oven is designed to give such a match.

Like any transmitter you can't just use it without an aerial, it will destroy the transmitter - and not work well either.

though, you would be surprised how well a transmitter works straight out the end of a length of tuned waveguide

edit, I have done that on 10 and 24 GHz quite successfully

davenn · Aug 3, 2017

flatfootskier said:
I can think of 500-600 reasons why this is a bad idea...

and yet you couldn't even give me one or two reasons

you DO NOT want to be using that sort of power level or a terrestrial point to point, you will cook ( pun intended) people and other living organisms

the only real valid reason for that much poser would be for doing amateur radio moon-bounce.

throbscottle · Aug 4, 2017

MrAl said:
Yes we only have 120vac here so it's not as good. I wish that they started using 230vac long ago. Looks like we are stuck with it.

I thought you guys had "bi-phase" mains power, so you could get 240v for electric ovens. Although I suppose running plug in appliance with 2 live wires isn't a good idea...

JimB · Aug 10, 2017

Have a look at this:

https://www.n5dux.com/ham/files/pdf/High Power Magnetron Transmitter.pdf

JimB

flatfootskier · Aug 10, 2017

throbscottle said:
Although I suppose running plug in appliance with 2 live wires isn't a good idea...

We do it in the UK though - centre tapped at earth, and yellow...

throbscottle · Aug 10, 2017

Huh? You talking about site transformers? CTE... But the difference is it's 55v live, not 115v. A lot less deadly :/

GromTag · Aug 10, 2017

A moon bounce signal.... Hmmm, lets see here, just watch out for space debris that might bounce the signal somewhere else and turns some ones house into a popcorn bash party. And 2, be sure not to hit those really expensive Geminids, Leonids, or Orionids Sattelites. Might be charged a big bill to replace those gems....

The Wifi use, the signal would have to ride the wave at some point during its stable points as most Magnetrons can self resonate unless cranked up in frequency. As far as I know on that.

m3vuv · Dec 21, 2018

using a sat dish with this,is it gonna be some secret death beam wheapon? m3vuv

JimB · Dec 21, 2018

m3vuv said:
,is it gonna be some secret death beam wheapon?

Could be useful at Gatwick airport.

JimB
(GM3ZMA)

unclejed613 · Dec 28, 2018

davenn said:
it has been done and varies well enough for ATV which is reasonably wideband ...
I do have the paperwork for a project presented in 73 Amateur Radio mag of some years back, that an amateur radio op used for doing ATV on 2.4GHz using around 500W microwave magnetron

just wondering, how linear is the cathode voltage/vs/output power curve? there is a cutoff threshold where current doesn't flow in a magnetron, as well as shifts in the output frequency caused by cathode voltage changes.

unclejed613 · Dec 28, 2018

m3vuv said:
using a sat dish with this,is it gonna be some secret death beam wheapon? m3vuv

interestingly, that's how RADAR was discovered...

Microwave cooker modulation

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