> hello,
> i need to calculate the noise variance of AWGN. i have the following info
>
>
> Noise power at the receiver:
> Boltzmann’s constant -228.6 dBW/K/Hz
> Bandwidth = 33 MHz 74.4 dB
> Temperature 20 oC = 273K+20K = 293K 24.7 dB
> Noise figure of the LNB 1.0 dB
> Noise power= -128.5 dBW
>
> i used the following formula
> Gaussian_sigma = 0.5 * sqrt(2) * ( 10^(0.05 * noise_level_dB ) )
> i put -98.5 dBm=noise_level_dB, the results comes 2.8150e-007 as noise
> variance, this is very low.
> Can anyone tell me where is the mistake.

You've totally lost your units -- 2.8e-7 what? Volts? Into what
reference impedance? Amps? Into what reference impedance?
meters/second? Newtons? Pounds per square inch? Into what reference
impedance?
Go back to your noise power and convert it to watts. The calculate your
noise level in your desired units, given your desired reference
impedance. I assume you want volts, into 50 ohms, but how would I know
that from your post?
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

Reply by sunshineshuvo●November 2, 20102010-11-02

hello,
i need to calculate the noise variance of AWGN. i have the following info
Noise power at the receiver:
Boltzmann’s constant -228.6 dBW/K/Hz
Bandwidth = 33 MHz 74.4 dB
Temperature 20 oC = 273K+20K = 293K 24.7 dB
Noise figure of the LNB 1.0 dB
Noise power= -128.5 dBW
i used the following formula
Gaussian_sigma = 0.5 * sqrt(2) * ( 10^(0.05 * noise_level_dB ) )
i put -98.5 dBm=noise_level_dB, the results comes 2.8150e-007 as noise
variance, this is very low.
Can anyone tell me where is the mistake.
thanks in advance
Reza