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calculate noise variance of AWGN

Started by sunshineshuvo November 2, 2010
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


On 11/02/2010 07:51 AM, sunshineshuvo wrote:
> 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