On Wed, 15 Sep 2004 12:56:16 +0200, "Thierry" to answer direct see
http://www.astrosurf.com/lombry/post.htm wrote:

But usually, in propagation program (VOACAP, etc), the power strength at
receive expressed in dBW is far below such values. I read somewhere the next
equivalences :
- (minus) 93 ~ S9+10, -103 = S9, -127 = S5, -151 = S1.

With -93 dBW for a S9+10 signal at receive, that 'd mean that the power 'd
be only P(W) = 10^ (dBW/10) = 0.7 watt ?
IMHO this power is much to low... What is wrong in this relations (or in my
interpretation) ?

Hi Thierry,

S-9 is the reference point for a 50µV signal into the receiver's 50
Ohm input. This is -73dBM (level below one milliwatt). Translating
to levels below one Watt is performed by subtracting another 30 (the
milli) dB - hence -103dBW.

Power is a curious thing. Transmitter efficiency as measured by the
target population that receives the signal is pitiful. If every
person on the planet had a radio that picked up your 100W signal with
S-9 level, you would be pumping 99.9% of your 100W into the void
without anyone missing it anywhere. Efficiency 0.1%

Given that you are NOT heard by everyone (they don't care to listen),
then transmitter efficiency plunges at least 7 or 8 more orders of
magnitude. Efficiency 0.00000001%

73's
Richard Clark, KB7QHC