Talk:Link budget

From Wikipedia, the free encyclopedia
Jump to: navigation, search
WikiProject Telecommunications  
WikiProject icon This article is within the scope of WikiProject Telecommunications, a collaborative effort to improve the coverage of Telecommunications on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
 ???  This article has not yet received a rating on the quality scale.
 ???  This article has not yet received a rating on the importance scale.
 

FSL Equation[edit]

FSL (dB) = 32.45 dB + 20*log[frequency(MHz)] + 20*log[distance(km)]

FSL (dB) = 36.6 dB + 20*log[frequency(MHz)] + 20*log[distance(miles)]

FSL in meters[edit]

I disagree with this formula:

FSL (dB) = -27.55 dB + 20*log[frequency(MHz)] + 20*log[distance(m)]

it should read:

FSL (dB) = 29.45 dB + 20*log[frequency(MHz)] + 20*log[distance(m)] since log of 1000 (number of meters in a km) = 3.

Kgrr (talk) 14:06, 1 October 2008 (UTC)


The formula is correct. The formula, with lambda equal to c/f, is

FSPL = ((4 * pi * d * f)/c)^2

With d in meters, f in MHz (= 10^6) and c equal to 3 * 10^8, we obtain

FSPL = ((4 * pi * d * f * 1 * 10^6)/(3 * 10^8))^2 = ((4 * pi * d * f)/(3 * 10^2))^2 = (0.041887893 * d * f)^2

Expressing this in decibels gives us:

FSPL(dB) = 10 * log10(0.041887893 * d * f)^2 = 20 * log10(0.041887893 * d * f) = 20 * log10(d) + 20 * log10(f) - 27.56 dB

ParadiseLost711 (talk) 18:45, 4 January 2009 (UTC)

so for 100 meters at 2,400 Mhz using formula 1.
FSPL(dB) = 20*log[4*π*distance/wavelength] = 20 log [4π * 100 m / (300/2400)m ]
= 20 log (10053) = 80.5 dB
and for 100 meters at 2,400 Mhz using formula 2.
FSPL(dB) = 20 log (0.1 km) + 20 log (2400 mhz) + 32.45 dB = -20 + 67.60 + 32.45 = 80.05 dB
and for 100 meters at 2,400 Mhz using formula 3. (100 meters = 0.1 km)
FSPL(dB) = 20 log (100 m) + 20 log (2400 mhz) - 27.56 dB = 40 + 67.60 -27.56 = 80.04 dB
and for 0.0621 miles at 2,400 Mhz using formula 4. (100 meters = 0.0621 miles)
FSPL(dB) = 20 log (0.0621 mi) + 20 log (2400 mhz) + 36.6 dB = -24.14 + 67.60 + 36.6 = 80.05 dB
OK ... My bad. It checks.Kgrr (talk) 16:19, 5 January 2009 (UTC)

The link to "Point-to-Point Link budget calculator" is to http://www.ligowave.com/linkcalc/ which requires a login is there not free, and either that is noted, or removed. --144.243.4.103 (talk) 16:44, 28 June 2010 (UTC)