From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Fri, 17 Aug 2001 12:17:23 +0000
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Subject: Re: LF: 183 carrier received in ZL
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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