# Phase shifts for cable VOP

Question asked by tigerblood on Mar 3, 2011
Latest reply on Mar 10, 2011 by SOLT_guy
I am a novice with network analyzers and I have some confusion interpreting the wrap-around phase-shift and want to understand how to fundamentally interpret this.

A method of measuring Velocity of Propagation for a cable is measuring the total phase-shifts across a frequency range and applying it to some formulas to obtain VOP.  But before we even talk about the formula, I just want better understanding of the phase-shift.  When I think of phase-shifts, I think of a sinusoidal signal lagging/leading a reference signal.  So when I see the wrap-around phase-shift every 360 degrees, is it correct to interpret the phase-shifts as a lag/lead in the signal?

And for the cable we are measuring to calculate VOP via the phase-shifts, I've been informed at the starting frequency we are measuring, the phase should start at a NEGATIVE phase in order to get the 'correct' total phase-shift for VOP calculation.  Why negative?

Thanks !