More on cable modeling

In our efforts to understand cable models a little better we took some measured data from Analog Devices ( Analog Dialogue, Vol 38, July 2004, "An adjustable cable equalizer combines a wideband differential receiver with analog switches", Johnathan Pearson) and an approximate expression provided by David A. Johns and Daniel Essig,( "Integrated circuits for data transmission over twisted pair channels", IEEE Journal of Solid State circuits, March 1997. A little dated but very useful, since this is one paper that actually had something we could get our hands around and use practically.)We used MATLAB to generate the loss characteristics as per David Johns et al's paper and plotted it along with the Analog Devices data. From this it appears that at small cable lengths there is generally good agreement between the two sets of data. As cable lengths increase the correspondence gets worse and worse. If one has to use the approximate expression, then a correction factor of from 2.5dB to 7.5dB may be needed to get closer estimates using the theoretical approximate expression. The results are in the "Engineer's Corner" on our website at www.signapro.biz.