>Formula for free-space loss (line of sight): > >L = 32.4 + 20Log(F) + 20Log(d), where L is in dB, F in MHz, d is in km > >To calculate the signal received: > >Ps = Po + Gt + Gr - L, where Po = power in dBm, Gt, Gr = gain in dBi >----------------------------------------------- >Example: >using d = 2.2 km (i.e. 1-mile), Po = 0 dBm, dipoles for antennas G = 2.1 dBi,
result is: >L = 92.1 dB >Ps = -137.9 dBm > >to calculate SNR = Ps - Pn >solve Pn = -198.6 + 10Log(Te) = 10Log(B), where Te is system noise >temp, B is bandwidth in Hz >Pn = -138.8 dBm if Te = 2100K and B= 500 Hz >Te = Tsky+Tant+Tr, where Tsky (50-MHz) is about 2000K at 6m Tsky dominates over typical receiver noise figures; Tr = 80K for NF=1 dB, K3 sensitivity is -138 to -140 dBm with 500-Hz filter >SNR at 2.2 km (1 mile) = 0.9 dB > >These formula do NOT work for over horizon paths, of course, since >there is additional loss due to refraction and ground-wave losses. and perhaps enhancement due to reflections >I have a spreadsheet program that you can merely enter the >parameters (numbers) and get an answer: >http://www.kl7uw.com/MROCalc.xls > >Note d is in millions of km so to enter d in km divide the number by 1,000,000 Program was written to analyze free-space signals from spacecraft so d is in units of million km. >Have fun! 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 50-1.1kw?, 144-1.4kw, 432-100w, 1296-60w, 3400-? DUBUS Magazine USA Rep [email protected] ====================================== ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
