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

...

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%

You really put the finger on something that I ignored during 25 years of ham
radio, hi !...
I know the correspondence between power expressed in dB or dBm, dBW but I
never see that under that angle...

Thanks
Thierry, ON4SKY

73's
Richard Clark, KB7QHC