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Measuring DUT hot transmitter return loss.

Question asked by glemire on Jul 21, 2014
Latest reply on Jul 25, 2014 by Dr_joel
I am using a PNA5225A to measure the transmitter and receiver return loss measurements for multiple standards (PCIe 1/2/3) SATA (1/2/3), 10GKR, SGMII etc. All of these standard require a hot transmitter measuremenst with the DUT transmitter actively transmitting a standard pattern (LFSR31, nyquist/2, etc).

I have several questions.

1) the amplitude of my DUT transmitted waveform is about 1V pp. In general do you recommend using attenuators when measuring an active device with this ampitude. 

2) I have my IF_BW set to be about 1kohm. I am sweeping from 10MHz-18GHz in 10 MHz steps. This seems to be a reasonable value, but do you recommend using i) averaging, ii) smoothing and iii) differant IF_BW setting?

3) I notice that when I reduce the IF_BW, the sweep takes a longer time. From what i understand reducing the IF_BW will reduce the random noise and lower my noise floor, but I am not sure why the sweep would take longer. I assume the IF filter is right before the ADCs in the receiver. 

4) anything elsethat you can recommend when doing this type of a hot measurement?

Thank you
Guy Lemire