On Sun, Jan 06, 2013 at 06:29:15PM +0100, Markus Vester wrote:

> The same Czech programme is also transmitted from Topolná on 270
> kHz, so that one would more likely be the heater. Interestingly the
> crossmodulation source is almost twice the frequency as the victim. Well
> almost, but not exactly - so that I still can't think of a simple physical
> mechanism to explain the asymmetry.

If one modulates a carrier simultaneously in phase and amplitude (with
the same audio signal), sidebands of the AM and the PM can (partially)
cancel each other on one side of the carrier, while reinforcing each
other on the other side. Thus, although one doesn't get a pure SSB
signal, one could get asymmetry.

Could this be the mechanism here; in other words, can ionospheric heating
produce both and amplitude and phase modulation?

73, Pieter-Tjerk, PA3FWM