The Legon Effect - Demonstration of Coherent Thermal Radiation emitted by a coffee mug filled with hot water.
A universal (ku-band) LNB for a TV satellite dish is connected through an ordinary satellite meter to a satellite receiver, which supplies power through a coaxial LNB signal cable.
As the mug containing hot water is brought closer to the feedhorn of the LNB, the meter responds with both audible squeal and visual LED display. Further movement towards the LNB yields a series of peaks and troughs in the signal level. Careful measurement shows that the wavelength of the detected radiation is 27.7 mm, corresponding to a microwave frequency of 10.8 GHz.
Since the frequency of the local oscillator in the LNB is set to 9.75 GHz, the intermediate frequency which is detected by the meter is 1.07 GHz. The meter circuit seems to be broadly tuned to this IF, which is within the normal operating range.
Explanation: All objects with a temperature above absolute zero emit electromagnetic radiation, in a continuous spectrum which extends into the 3 cm waveband at room temperature. A continuous spectrum of frequencies is therefore present in the radiation emitted by the mug, and a signal peak is detected when there is an integer number of half-wavelengths in the distance between the mug and the LNB feedhorn.
To have this effect, the radiation for a given frequency must be emitted with a constant phase relationship over distance - a characteristic of coherent radiation. The present findings are consistent with the conclusion that the energy being emitted by the coffee mug is coherent.
The demonstration also works with cold water in the mug - and indeed with other objects - but hot water in the mug is more energetic and gives a much stronger response.
John Legon, 6th January 2011. http://www.john-legon.co.uk/thermal.htm
