KN5L measurement of JSC 1318 windowed ladder line – MLL @ 4.2MHz

John, KN5L, published some interesting measurements he made of a recent purchase of JSC 1318 windowed ladder line. JSC Wire & Cable is now known as Seminole Wire & Cable, and this is their 1318 product.

Product with apparently similar specifications are sold by many ham retailers, they may or may not be sourced from Seminole.

Some sellers specify the % IACS rating of the copper clad conductor, usually 30%, some just don't mention it.

John carefully measured the DC resistance of his line section, and found that it reconciled well with the Copperweld datasheet for 21% CCS.

He also used a VNA to measure S11 of the line section with S/C and O/C terminations, and he gives links to the Touchstone files at the top of his page.

The O/C Touchstone file allows calculation of Zin. The O/C line exhibits resonance at 4.2MHz, at Zin=3.7Ω. His fuller set of measurements showed that Zo at 4.2MHz is very close to 400Ω. We can use those measurements to calculate Matched Line Loss (MLL).

Above, MLL is 0.50852dB/100m.

A graph was made of:

  • MLL calculated above from KN5L's measurements for 21% IACS line;
  • MLL inferred by the physical parameters for 21%, 31% and 100% cladding as described at A model of current distribution in copper clad steel conductors at RF;
  • An extrapolation of N7WS's measurements of Wireman 551 at 50MHz (where it behaves essentially as a 100% copper conductor). The extrapolation is unsafe because the conductors are unlikely to be as good as copper at 4.2MHz, and this will be an underestimate of loss; and
  • TLDetails estimate of MLL for Wireman 551, a similar line though specified as 30% IACS.

Above, the modelled current distribution in the conductor.


Above, the different values charted for comparison.

The closest value to the measurement is that found from the 21% CCS current distribution model.

The furthest from measured is TLDetails, and although it is for a 30% IACS conductor, it gives 65% higher MLL.

The 100% copper conductor model reconciles very well with extrapolation of N7WS's measurements.

We can reasonably draw the conclusion that the 21% CCS line has MLL a little higher than the 100% copper equivalent at 4.2MHz. Note that this is a single core conductor, stranded 21% CCS is likely to be worse.

John's measurement raises questions for the technical audience of the IACS specification of market products, and then their RF performance at the lower end of HF and MF.