Originally Posted by rib1948
I sailed from Tenerife to Madeira and was astonished
to get half the way near Islas Salvages
a call from Tenerife Traffic over a distance of 135 nm.
The reason is the antenna in Tenerife is located
at apr. 2.500 meter high (with 25 Watt).
I got a PM and will explain the argumentation.
With a very high antenna the power of 25 Watts is still suficient to provide a comunication over 135 miles.
The quality was very noisy , so I estimate that distance as a maximum.
The rangers of the Islas Salvages national park told me,
that they can listen regulary to transmitter based on Tenerife,
even handy comunication was possible some years before.
So the coverage of 135 miles is not a effect of a propagation abnormity.
When the line of sight is less, eg only 5 miles, than there is sufficient power for a good comunication.
In the area of the line of sight there is a power loss of 6 dB when the distance is doubled.
The power loss outside of the line of sight, yust over the radio horizon,
must be asumed to be quite high.
Only a small fraction of the VHF energy is bend.