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Time domain measurements on long cable - problem (E5070B)

Question asked by dvaluch on Nov 13, 2006
Latest reply on Nov 14, 2006 by dvaluch
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!  

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