Dear LF group,
ZL2CA wrote:
As half the circumference of the globe is nominally 20000 km, then
propagation between ZL and EU does not have a lot of difference between
long and short paths. The antipodean positions are ZL and Portugal. Any
minor tilt or disturbances in an "ionospheric shell" can influence the
angle of arrival for DX between EU and ZL. For amateur LF testing,
antennas are nominally omnidirectional, so if there does turn out to be
confirmed reception, the path will have worked itself out!
But the point is, since Europe 1 has a highly directional antenna
beaming in the long path direction, there is a large difference in the
ERP of the signal depending on whether it arrives by long path or
short path.
If I understand it correctly, the french text of the Europe 1 web
pages (http://home.worldnet.fr/~tvignaud/am/e1/fr-e1.htm) says the
forward gain of the antenna is 3, and signals off the back of the
antenna are attenuated by "1/1000", presumably a forward gain of
about 5dB, and -30dB front to back ratio. Taken literally, this would
mean a long-path signal of a few megawatts ERP, and a short path
signal of only a few kW ERP. If an amateur signal of 1W ERP is
generated with an omnidirectional pattern, it would be 60-70dB
down on the Europe 1 long path signal, but "only" 30-40dB down on
the short path signal.
So if the signals seen by ZL2CA are arriving by a short path, the
chances of amateur signals being detectable are much greater
than if they are arriving by the long path.
If the signals are going via a short path, other european
broadcasters with omnidirectional antennas should be considerably
stronger than Europe 1. Conversely, if the signal arrives by the
long path, Europe 1 should be somewhat stronger than the rest.
Cheers, Jim Moritz
73 de M0BMU
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