Hi, When I set the Conducted immunity test up for folks I ALWAYS add an attenuator on the front end of the spectrum analyser. Typically I use a 25 watt 10 dB pad followed by a 20 dB 1 watt pad. I use a good quality attenuator, and if accuracy is really critical, I characterise them and compensate in the software.
What I've seen is that setup using automated software, poorly tuned, work the signal source very hard. After a time this chap begins to put out transients that are faithfully amplified and end up at the front end of the SA. SA's seem to handle 30 dBm, just, but anything, even for the shortest time, over that and the front end goes. I've found that you should also include the 6 dB pad at the input of your coupling device. Apart from the Standard requiring it, it really does help. Also, don't rule out a degrading cable as the source of your problem Best regards, Derek Walton Schaffner USA RF Systems Specialist.
