```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&rsquo;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
impedance. I assume you want volts, into 50 ohms, but how would I know

--

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
```
```hello,
i need to calculate the noise variance of AWGN. i have the following info

Boltzmann&rsquo;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.