Vitaliy wrote:

> Gerhard Fiedler wrote:
>> 5000 mW / (1609 m)^2 = 1.9 uW/m^2
> 
> [...] and both times it was you who pointed out the mistake. ;-D 

I wish I could have contributed something more substantial :)

> 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 ;) 

Not really :)  Just adding that you could factor in that the "other"
antenna is highly directional and yours is isotropic; then the 2.6 kW could
go down by the ratio between their and your antenna. Howard mentioned that
there are antennas with a gain of 12, and possibly it could be even higher.
So a transmitter with 216 W or less could do it -- and, depending on the
application, it also may not be a full mile away. Bringing that together it
seems that in the end you could get in trouble with a 5 W transmitter, with
a highly directional antenna, 250 m away... (assuming that same RF power
means trouble, which I don't know whether it does).

Gerhard

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