On 17/03/2012 02:21, MatSav wrote:
"Roland wrote in message
...
In , at 15:01:49 on Fri, 16
Mar 2012, remarked:
That has been alleged to have happened on English south coast
shores/beaches which are screened from the local transmitter
by
high
cliffs but within range of French base stations.

Sometimes, exceptional atmospheric conditions can cause this
from
elevated inland points as well.

I was at the Great Dorset Steam Fair http://www.gdsf.co.uk at
Tarrant Hinton, and made some calls to friends who were
elsewhere
on the very large fair site. When I got the bill, I discovered
I
had apparently made calls in France *and* the UK within a few
seconds of each other.

The mobile phone systems utilise a transmission protocol known
as
TDMA (Time Division Multiple Access). In theory, this should
block connections where the propogation delay is more than 28
milliseconds (equating to a distance of about 90km). In my
case,
the nearest point of the French coast was at least 130km away -
so it shouldn't have been possible, but it definitely happened.

Coastal base stations (such as the one which you contacted in
northern France) can be adjusted to allow twice the normal
propagation delay, so that large areas of sea are covered.

Thanks Roland - I didn't know that. It makes sense, I suppose,
given that there are numerous reports of ill-prepared "sailors"
calling for assistance at sea by using their mobile 'phones,
rather than using a marine-frequency VHF radio.


I thought the relevant distances were 35KM and therefore 70KM for when
double-slots were in use (for long distance usage).

It sounds like something else is going on, but for the life of me I
can't work out what.