Checkout of a roll of Commscope 4510404 CCS RG11A/U – Zoc, Zsc based MLL calculation

Checkout of a roll of Commscope 4510404 CCS RG11A/U documented a simple and quick test of the matched line loss (MLL) of a roll of new RG11A/U just delivered. The test used is simple, and quite suited to the case where the far end of the cable is not accessible, eg buried inside the drum.

In this case, the far end of the cable was accessible and a series of measurements of impedance with a short and open termination could be made. This is a more comprehensive test, but involves more complicated calculations.

\(MLL=\frac{20}{2len} log_{10}| \frac{1+\sqrt{\frac{{Z_{sc}}}{Z_{oc}}}}{1-\sqrt{\frac{{Z_{sc}}}{Z_{oc}}}} |\; dB/m\\\)

The measurements were made at 1979 points linearly spaced (~15kHz) from 1-31MHz using a VNWA3E. Touchstone files were save of each scan and analysed in a custom Python script.

Above is a plot of MLL calculated from Zoc and Zsc of the 305m line section. Also plotted is a curve fit of the points from 15-31MHz to the model \(MLL = k_1\sqrt f+k_2f\). The departure of the measurements from the model are a result of insufficient copper thickness to deliver copper like performance. The departure is quite small at 7MHz, and progressively worse on the lower bands.

The plotted MLL reconciles with the spot figures published in Checkout of a roll of Commscope 4510404 CCS RG11A/U.

Above, the measurements also reveal the small reduction in velocity factor at the lower frequencies, a natural effect of transmission lines but somewhat increased by the CCS construction.

Note that not all CCS RG11A/U will behave exactly like this, though good quality cables using a 21% IACS 1.63mm (#14) CCS centre conductor should be similar.

Could you do this with a nanoVNA? Possibly, but I did a sweep of 2000 points in one pass and nanoVNA does not natively support that. But, try it and compare your results.