Induction cooktops and RFI?

wb4jfi at wb4jfi at
Thu Apr 12 22:57:45 CDT 2012

Thank you Karl, and others.

Maybe I should have been more clear... we are looking at replacing the electric cooktop in the kitchen of our house, which is used to cook food.

We were looking at using natural gas, which the house has, but someone suggested we look at induction cooktops instead.  They appear to be more efficient, and easier to clean.  But, they clearly generate significant magnetic fields that couple enough energy into the pot to cause it to heat up dramatically.  I am always concerned about devices that generate “powef” magnetic fields (wireless phone chargers, etc), since often they operate at higher than the power mains frequency, to be more efficient.  They also often create unwanted RF signals, either directly, or as a byproduct of the fast switchers used.  Hence my question.

Karl appears to have provided an on-point answer, that I may indeed need to be cautious.  High-technology giveth, and high-technology taketh away.  Oh well, I don’t do much LF listening anyway... and now I can have a test signal generator!!  Fire up burner three, with a five-quart pan 1/2 full of water for exactly 75kHz signal at –80dBm thirty feet away...

From: Karl W4KRL 
Sent: Thursday, April 12, 2012 10:43 PM
To: tfox at ; andre.kesteloot at 
Cc: tacos at 
Subject: Re: Induction cooktops and RFI?


Induction cooktops operate between 24 and 50KHz. There is probably a lot of potential for RFI near the range.

73 Karl W4KRL 

Terry Fox <tfox at> wrote:

Thanks Andre!  My spec an only goes to 3GHz.  The whole idea was to know what they (induction cooktops) do BEFORE I buy one.

Maybe you could camp out at the local Sears with your spec an, and test for me??

From: André Kesteloot 
Sent: Thursday, April 12, 2012 8:11 PM
To: Terry Fox 
Cc: mailto:andre.kesteloot at ; mailto:tacos at 
Subject: Re: Induction cooktops and RFI?

Well ,I have here a spectrum analyzer that goes to 200 MHz.

Buy me a similar cook- top, have it delivered free-of-charge to my castle, and I shall be pleased to investigate whether it nastily radiates  HF waves, or not .
This service will be at no charge to you 

Sent from my iPhone; eventual mIstAkEs should be blamed on the thickness of my fingers :-)

On 12 Apr 2012, at 19:48, "Terry Fox" <tfox at> wrote:

  From: Andre Kesteloot 
  Sent: Thursday, April 12, 2012 6:59 PM
  To: tacos at ; Terry & Judy Fox 
  Subject: Re: Induction cooktops and RFI?

  On 4/12/2012 18:31 PM, Terry Fox wrote: 
    Does anyone use an induction cooktop, and can tell me if there is any RFI from it to ham bands?
    Terry, WB4JFI


  We don't have an induction cook-top, but
  isn't the induction coil powered by the 60Hz mains ?

  I was more worried about the control circuitry, and if there is a solid-state switching of the element.  Since induction is designed to radiate a magnetic field (albeit at 60Hz?), if that field is controlled by higher-speed devices, there might me more radiation?  Or not.. 

  Do they do PWM for the control?  It also seems that there are a lot more “steps” in the control than a traditional electric cooktop.

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