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A couple of questions about IMD in PNA-X

Question asked by RAVONCAPD on Sep 30, 2009
Latest reply on Oct 12, 2009 by RAVONCAPD
While setting up to measure IP3 on the PNA-X (using external software not option 087) we noticed that the noise floor was at aprox. -70dBc with an input signal of -20dBm at freq. range 10MHz-6GHz with 600 points.
Setup consisted of standard measurment in 2-tone signal routing with Out1 and Out1 Src2 set to On,
frequency offset=1MHz
reciever B attenuator=10 dB.
Power calibration was preformed using U2000A power sensor at 0.05dB tolerance.

A second setup was attempted using ports 1 and 3 in default signal routing going to an external directional bridge (Agilent 86205A) with Out 3 replacing Out1 Src2 but otherwise using the same calibration. This setup resulted in -75dBc noise floor.
Any suggestions on how to improve the setup? Aplication note 1408-17 seems to say we should be getting around -90dBc with these setups.

Second question, we were told that when using an external amplifier to amplify Out1 Src2 we must use the power offset option to account for the amplifier, however any value in 'power offset' seems to change the power that the source power calibration locks on to. Is this correct or are we missing some step?

Thanks in advance