Gerhard Fiedler wrote:
> Maybe your intuition wasn't that wrong, after all... Probably when you
> divided 5000 by 2588881 (that's 1609^2), you took the 10^-3 of the result
> as meaning "milli", but with milli already going in, it's "micro":
>
> 5000 mW / (1609 m)^2 = 1.9 uW/m^2

This is the second time my math skills embarrass me.. and both times it was 
you who pointed out the mistake. ;-D

Then Howard Winter wrote:
> Hang on, chaps!  While the ratio of field strengths in the above 
> calculation is correct (1 : 0.0019) it's
> wrong to give them a dimension - the actual field strengths certainly 
> won't be the figures shown above.
>
> If you assume an antenna with no gain (isotropic, giving a perfectly 
> spherical radiation pattern) field
> strength of 100mW at 10m will be about 0.079 mW/m^2 (calculated using the 
> area of a sphere, 4 pi r^2).  Now
> isotropic antennae are kept in the same drawer as frictionless pulleys and 
> light, inextensible string - they
> are theoretical only, but a practical antenna for the appication under 
> discussion is unlikely to have a gain
> over isotropic of more than about 2 or 3.  You'd need a highly directional 
> antenna with a gain of about 12 to
> get 1 mW/m^2, and it's very unlikely that that's what would be used in 
> this case.

What you are saying about field strengths makes perfect sense, but I guess 
in this particular case I was only interested in the ratio. Jose Da Silva 
said:

> Your 100mW may still be overshadowed by a transmitter a mile away
> pumping out 5W....

Which is obviously wrong, assuming the same radiation pattern for both 
antennas a transmitter one mile away would have to output 2.6 kW to match 
the signal of the local 0.1 W transmitter (Gerhard, let me know if my 
calculations are wrong again ;)

Vitaliy


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