Matched Line Loss of generic RG6/U Quad Shield CCS

This article documents a measurement of Matched Line Loss (MLL) of a 35m test section of generic RG6/U Quad Shield CCS.

It has become impossible in recent years to buy low cost RG6/U with solid centre conductor locally, and the imported product with solid copper conductor is prohibitively expensive (~$6/m as against $0.35/m for the CCS).

The CCS cable does have near copper like performance at UHF and above, but what is its behavior at HF?

Above is calculated MLL from a S11 scan of the test section with S/C and O/C termination. There is a little ripple on the response due to measurement error. The graph also has a curve fit, MLL=0.0285f^0.1506 (F in MHz).

Were the conductors homogenous and subject to well developed skin effect, and on account of the fact that conductor loss dominates in this type of cable, we would expect that MLL=k*f^0.5, but the exponent in the curve fit is quite a low lower at 0.1506, evidence that simple skin effect is not well developed, the CCS conductor apparently having too little copper cladding to exhibit copper like performance in this range. MLL at 1MHz is about four times that of an equivalent copper cable.

The results cannot be inferred for other low cost cables as they are quite likely to use different cladding thickness. This sample certainly shows worse MLL than some Belden CCS RG6/U cables. If you want to use this stuff at HF, measure your own stock to determine its suitability.

A quick confirmation can be obtained from the Return Loss (Zref=75Ω) plots of S/C and O/C sections.

The above chart from AIM 910B (the ‘current’ version 914 is broken, 910B is less broken) is of Return Loss (upside down… a quirk of AIM software) at at the cursor (3.721MHz) the Return Losses are 2.72 and 2.19dB, so MLL is approximately (2.72+2.19)/4dB/35m=1.23dB/35m=0.035dB/m which reconciles with the previous chart.

As a side observation, the disparity between the Return Loss for O/C and S/C (with circles) shows how unsound is the ‘classic’ / popular Half Return Loss method base on S/C or O/C alone.