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Technology Stocks : LAST MILE TECHNOLOGIES - Let's Discuss Them Here -- Ignore unavailable to you. Want to Upgrade?

To: Scott C. Lemon who wrote (6450)	2/18/2000 9:40:00 PM
From: Dennis O'Bell	Read Replies (1) \| Respond to of 12823

Hi Scott... The calculation he cites is in any book on communications engineering or antenna handbook. One assumes an isotropic source of power at the center of a sphere, so the power density per unit area will be the reciprocal of the surface area of the sphere. power density = (transmitter power)/(area of sphere of radius R) power density = (transmitter power)/(4 pi R^2) Next, one assumes an isotropic receiving antenna which has an effective aperture depending on wavelength aperture area = wavelength^2/(4 pi) Just take the product and express the ratio in decibels 10 log (1/(4 pi)^2 * ((0.186 / f)/R)^2) 20 log (.186/(4 pi)) - 20 log (f) - 20 log (R) the .186 is from speed of light in miles/microsecond Et voila... To take account of antenna gains, be sure they are relative to an isotropic antenna - the usual theoretical benchmark that is unrealizable in practice but simplifies formulas.