"Ian White, G3SEK" wrote in message
...
Fractenna wrote:
A radar telescope--using a dish--can be dangerous and the EIRP can be
megawatts.

More techno-folklore.

The only heating power available is the power supplied up the feedline.
"Magnification" by the antenna is irrelevant, and EIRP figures only
serve to scare people.

Actually, the exact opposite is true. RF hazards are a function of power
density (mW/cm^2 or W/m^2). The higher the antenna gain is, and the
higher the far-field EIRP, the larger the aperture area must be and
therefore the lower the power density becomes.

Ok Ian
I think that I can compute it now. I know the gain and MW sent by some RT,
the RF limits for the health, etc.

Thanks.
Thierry, ON4SKY



The most dangerous antenna is the smallest, for example, an open-ended
waveguide or a small horn. That is because all the available power is
concentrated into such a small area. Looking into an open waveguide is
like looking into the barrel of a gun - you don't do it until you've
made darn sure about the other end!

But if you take that horn outside and mount it on a big dish where it's
hard to come anywhere near, it is immediately much safer. And the larger
the dish is, the smaller the RF hazard becomes.

Bottom line: "EIRP" and "RF hazard" don't belong in the same sentence -
except this one.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek