Dear all,
I wanted to do a S11 measurement in Time Domain on rather long cable (~420ns) and didn't manage. Therefore I would like to ask for an opinion what is going on.
We have the E5070B machine, 300kHz-3GHz with a time domain option.
I need to match several cables to have a same electrical length. As the far end of the cables is not accessible one way how to do it is to put short there and measure S11.
However, it seems the network analyzer cannot digest it. Measured phase is just chaos, electrical delay compensation doesn't give any reasonable results. S11 in time domain shows one peak at somewhat 32ns instead of 2*420=840ns. That is clearly wrong.
Does it have something with the start frequency, number of points, bandwidths? Is it even possible to do such a measurement with NWA starting from 300kHz?
How would you measure such long cables? We also have some even longer, how to measure absolute time delay of them?
Thanks a lot!
I wanted to do a S11 measurement in Time Domain on rather long cable (~420ns) and didn't manage. Therefore I would like to ask for an opinion what is going on.
We have the E5070B machine, 300kHz-3GHz with a time domain option.
I need to match several cables to have a same electrical length. As the far end of the cables is not accessible one way how to do it is to put short there and measure S11.
However, it seems the network analyzer cannot digest it. Measured phase is just chaos, electrical delay compensation doesn't give any reasonable results. S11 in time domain shows one peak at somewhat 32ns instead of 2*420=840ns. That is clearly wrong.
Does it have something with the start frequency, number of points, bandwidths? Is it even possible to do such a measurement with NWA starting from 300kHz?
How would you measure such long cables? We also have some even longer, how to measure absolute time delay of them?
Thanks a lot!
Step #1: READ THIS ARTICLE!: http://na.tm.agilent.com/pna/files/eld.html
Step #2: Make sure you are in stepped sweep mode (if available). If you are unsure, then slow the sweep down until you see no more changes in the displayed S11 trace.
You probably also want to limit the frequency span (decrease the stop freq.) and increase the number of points in order to limit the phase change per point. Does this cable support the higher frequencies? And if so, how much loss per foot does it have? You can't measure a long cable properly if it looks essentially like a load!
Try the above and report back.
I should add that for measuring the length of very long cables, you generally want to use the lowest frequencies possible and the least amount of frequency span that will get you the desired distance resolution needed. Also, you want to use the highest possible power (fortunately, this typically occurs at the lowest frequencies.)
Did you perform a cal before the measurement was made?