Two identical coffee mugs, one filled with hot water and the other with cold water, are placed in turn at some distance in front of a ku-band LNB. The distance is reduced until the satellite meter responds with an audible squeal and the LEDs light up. Both hot and cold mugs give a response, but the mug containing hot water is detected at a greater distance from the LNB than the cold mug. The general effect with hot water is more "energetic".



My tentative explanation for this phenomenon was that all objects with a temperature above absolute zero emit electromagnetic radiation in a continuous spectrum, which extends into the 3 cm satellite waveband at room temperature. A continuous range of frequencies was therefore present in the radiation emitted by the mug, and through a resonant effect, a signal peak was detected when there was 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 had to be emitted with a constant phase relationship over distance - a characteristic of coherent radiation. The findings seemed to be consistent with the hypothesis that the energy being emitted by the coffee mug was coherent.



Some commentators in the discussion group asserted that the wave effect was caused by the leakage of local oscillator signal from the LNB being reflected back from the coffee mug. Several tests have shown, however, that the effect of LO leakage is very small. This was established by bringing up a second identical LNB face to face with the first LNB, and toggling the power on and off. With the two LNBs set to the same frequency band and polarization, it was possible to detect a change in signal, but this could only observed at close range and was at least an order of magnitude less than the coherent wave effect. The LO signal is always present inside the LNB at a much higher level than any signal that might be reflected off a coffee mug, especially since both the ceramic of the mug and the water are good absorbers and poor reflectors of microwaves; and in any case, two signals of the same frequency do not give a difference product in the IF waveband.