U shd have noise source and FFT option in the SA(Its by default).Get the output displayed on the SA in FFT format and find the maximum peak at the desired frequency and max peak at the base level.The difference between will get u the noise ratio. Just try it. or use noise source and compare with the output signal and using the formula of SNR(just check this) u will get it.
0.8 dB is a very good and very low value.
When NF values are so low, the uncertainty became dominant.
The keys to do a measurement (not say good measurement) is the followings:
1) an accurate Noise Source
2) a Noise Figure Meter
3) leave the SA to people working with 5 dB NF or worse.
4) read Agilent AN57-1 and 57-2
I think you will check input noise source level and just read the output level at a specified frequency. Since you know the amplifier gain, you can calculate the noise figure.