Our new 2M EME station will have Adaptive Polarity capability via MAP65. MAP65 requires that received signals from the Horizontal and Vertical planes of our antennas arrive at the receivers in our shack precisely in phase with each other. We used a VNA to precisely measure coax cable length…

Source: EME Station 2.0 Part 3 – Phase Tuned Receive Coax Cables

We are continuing to make progress on our new 2M EME Station. The MAP65 adaptive polarity aspect of our plans requires that the phase relationship between the Horizontal and Vertical elements of our antennas be precisely maintained by our receive coax cables.

The construction of these coax cables required us to use a Vector Network Analyzer (VNA) to precisely measure and equalize the electrical lengths of our receive-coax cables. We know that a 1/4 wavelength section of coax cable which has an open-circuit at one end will appear as a low (resonant) impedance at the opposite end. If we use a VNA to precisely measure the minium resonant frequency of our coax cables in this way, we can use a simple formula to determine the cables’ lengths.

The article associated with the link above explains how a VNA can be used to measure the length of a coax cable. A frequency accurate antenna analyzer can also be used to make these measurements.

Fred, AB1OC