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![]() "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 |
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