PSP is a little complicated to set up - it's got rather clearer
in the UI from IC5032 onwards (it now allows you to select
from a list of frequencies, for example).

Here's what I'd expect you to set up:

1. RF signal as DC - no sine wave input here (you can
   treat it as small signal, unless you're trying to measure the
   noise/s-parameters in the presence of a blocker, or a
   signal driving the mixer into compression).
2. LO as large, of course. This means that your PSS
   frequency will be the LO frequency, and hence 1.8GHz.
3. I always recommend using sweepmode "relative"  in
   PSP, because it's easier to understand. The frequency
   of each port is then determined by f+k*PSSfund where
   f is the spot frequency, or sweep range of the sweep.

   So in this case, you'd  have port 1 as the RF port,
   port 2 as the IF port. No need to have the LO port
   mentioned at all (unless you're trying to find the
   s-parameters between IF and LO or RF and LO, which
   I doubt).

   Then have either:

   frequency sweep around 1.9GHz (or a spot frequency)
   Input port harmonic as 0  (no shift)
   Output port harmonic as -1 (shifted down by 1.8GHz)

   or

   frequency sweep around 100MHz (i.e. output frequency)
   Input port harmonic as 1 (to get to input frequency)
   Output port harmonic as 0.

Absolute mode is very confusing, because the frequency
sweep is always used for the first port in the mode, but
the remaining ports are shifted relative to the input port.
Relative mode is where the "harmonic" number specifies
the amount of PSSfund shifts on that part relative to
the frequency sweep.

Hopefully that will clarify things a bit?

Regards,

Andrew.