Andrew Beckett
Senior Fellow
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Life, don't talk to me about Life...
Posts: 1742
Bracknell, UK
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In this case the reference side band is most likely to be (0 0) because if it's an amplifier, the transfer function that you're interested in for the purposes of calculating the noise figure is that the output frequency is at the same frequency as the input. In general the reference sideband determines the input frequency given the output frequency sweep - i.e. for a specified output frequency, fin=fout+k1*f1+k2*f2 where f1 and f2 are the "large/moderate" signal frequencies, and k1 and k2 are the number of shifts to be applied.
Recent versions of DFII give you a means of selecting the reference side band from a list - so you can more easily see the frequency range. That said, you still need to ensure you've got the right transfer function, so simulating with qpxf is often useful anyway to ensure you've got a reasonable transfer function.
With an amplifier, the two large signals are effectively blockers which are not needed for correct operation of the amplifier - they're presumably only there because you want to see the effects of compression and/or intermodulation when doing the noise analysis.
Regards,
Andrew.
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