NF and sensitivity calculations made easy

• Subject: [amsat-bb] NF and sensitivity calculations made easy
• From: Bob Nielsen <nielsen@xxxxxx>
• Date: Mon, 21 May 2001 08:01:04 -0700
• User-Agent: Mutt/1.2.5i

```In case the various formulas floating around are confusing some of you,
(the articles referenced are several years old and not readily
available) it all boils down to the relatively simple equation for
noise power, N= KTB, where N is the noise power in watts, K is
Boltzmann's constant (1.38062 x 10^-23 Joules per degree K), T is the
temperature in Kelvin and B is the bandwidth in Hz.

Since Boltzmann's constant was pounded into my head in a physics class
some 40+ years ago, that number was all I have ever needed to remember
in order to calculate noise power.  Converting Boltzmann's constant
to decibels give us -228.6 dBW/deg K/Hz.

Converting to dBm adds 30 dB and converting to room temperature (20 C)
adds another 24.4 dB to give -174.2 dBm, usually rounded off to -174
dBm.  All you need to do next is add in the factors for the bandwidth,
noise figure and S+N/N and you have your system sensitivity.

--
Bob Nielsen, N7XY                          nielsen@oz.net
Bainbridge Island, WA                      http://www.oz.net/~nielsen
IOTA NA-065, USI WA-028S
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