>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
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