Measure MLL using the half ReturnLoss method – a spot test with a hand held analyser
At Exploiting your antenna analyser #14 I gave an explanation of the method of approximating MLL of a line section by taking the average half Return Loss with o/c and s/c terminations.
This article demonstrates the technique using the Rigexpert AA-600 analyser in hand held mode.
The task is to assess whether a section of RG58A/U coax has MLL at 3.5MHz similar to specification or not.
The specification loss of 10.13m of RG58A/U has MLL=0.29dB.
Above, the first test with an o/c termination. Return Loss is 0.4dB.
Above, the second test with an s/c termination. Return Loss is 0.7dB.
The average of half Return Loss is (0.4+0.7)/4=0.28dB. Given the tenth dB resolution of the measurements, the measured value supports the proposition that the cable is good.
It is worth making set of male and female s/c terminations in your favourite connector types for such measurements.
If your antenna analyser purports to make a MLL measurement in one pass, and it doesn’t matter whether the termination is o/c or s/c, the two measurements above demonstrate that it DOES matter in some circumstances. The best way to determine if it matters in some scenario is to make both measurements, if they happen to be the same then averaging them is a no-brainer.
Watch the blog for continuing postings in the series Exploiting your antenna analyser. See also Exploiting your antenna analyser – contents.