[Fwd: LF: Luxembourg Effect.]
Mon, 31 Aug 1998 09:27:38 -0400
Peter Martinez wrote:
> >From Peter Martinez G3PLX Kendal Cumbria:
> I too can hear the broadcast audio modulation on the 139 kHz signal at night, but had assumed it was cross-modulation from a nearby BC transmitter. But if we are all hearing different programs, then this must surely be the Luxembourg effect. Reading up about it, the effect will be most pronounced when the modulating transmitter is in the 0.8-1.4 MHz region, since this band is where an upward-going wave will be absorbed most by the D-layer: it's the gryo-resonance at which frequency electrons tend to spin around the earths magnetic field lines. What happens is that the medium-wave RF heats the D-layer in sympathy with the audio, and this temperature variation modulates any other signal that is attenuated by the D-layer. LF waves are certainly more affected by the D-layer than higher frequencies so we hear this modulation on 139kHz. For Rik, the audio we are all talking about is modulated ONTO the carrier at 138.82, so you can hear it best by zero-beating with it on USB, or even better
> on an AM receiver.
> SInce it is medium-wave transmitters that are more likely to heat the D-layer, it could be that the German programs heard modulating the 138 kHz signal are coming from a medium-wave transmitter carrying the same program and not from the longwave ones, although if the longwave transmitters are high power....
> Most mediumwave transmitters will not radiate any power vertically upwards, so the strongest effect might not be from a mediumwave transmitter exactly on the path, but offset a bit so that part of a ring of D-layer around the transmitter is along the path. I will try to identify which signals I am hearing in the modulation.