noise variance of AWGN calculation

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