They are 50 ohms nominal impedance, but their VSWR tends to be higher than a typical spectrum analyzer. Let’s say the VSWR of your SA44B had a typical return loss of 16 dB (probably even worse than this at high frequencies). If you add a 3 dB pad to this, it increases to 22 dB, assuming it’s a good pad with excellent return loss (signal goes through pad, reflects, then through pad again). Add a good 6 dB pad, and return loss would be 28 dB. You could even try 10 dB pads, which would give you maybe 36 dB return loss, but then your signal might be noisy enough that the extra return loss isn’t worth it…
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