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Sunday, 21 August 2016

Reflectometer measurements with the SMA Spectrum Analyzer


I just did some trials to use the SMA Spectrum Analyzer as a reflectometer using my software (see previous post).

You need:

  • 1x SMA Spectrum Analyzer 138MHz-4.4GHz
  • 1x Noise Generator - I used the cheap BG7TBL one (20 Euro at eBay)
  • Cables and adapters
The setup is shown in this picture:

Using my software, the reflected patterns can be shown in the spectrum:

The patterns are characteristic to the location of the cable fault (i.e. a not properly terminated cable).

Measuring the distance between the "valeys", you can determine the location of the cable fault, if you now the cable propagation speed. The above pictures shows a non-terminated cable with  600mm length.

This picture shows the pattern of a non-terminated cable with 2300mm length.

This resulted in the following measurements:

57 MHz > fault at 2300 mm
200 MHz >  fault at 600 mm

Using simple math, we can calculate the location of a cable fault at unknown distance, measuring the frequency-width of the "valley". Note that this requires that the cable to be measured has the same cable propagation speed as the cables used for determination of the calculation factor.

I am considering a calculation button on my software... Does this interest anyone?


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