Ronja Twibright Labs

Measuring Tetrapolis NED with bertest

Measurement of Ronja Tetrapolis Noise Equivalent Distance with Bertest


What is NED

NED (Noise Equivalent Distance) is a distance between transmitter (TX) and receiver (RX) at which the energy of noise that is mixing into the signal is the same as the energy of the received signal. In other words, it's distance at which SNR (Signal to Noise Ratio) is 0dB.



  • Mirror
  • A computer with 1 free full duplex network card or 2 free network cards
  • Linux where C programs can be compiled.
  • GNU R installed
  • Bertest installed
Postscript / PDF / EPS / BIG png / SVG (Inkscape)

Distance adjustment

First, setup bertest for packetloss measurement. Run the measurement and adjust the distance between RX and TX so that both second and third columns show numbers with 50 roughly between them (0 and 100 should never occur if possible). Example output:

1102885377.652586000    13.868  77.637  1024    2224
1102885378.222727000    14.649  80.372  1024    2224
1102885378.792451000    17.969  83.692  1024    2224
1102885379.362579000    17.188  85.157  1024    2224
1102885379.932404000    22.364  84.961  1024    2224
1102885380.502458000    15.528  79.883  1024    2224
1102885381.072232000    13.379  76.661  1024    2224
1102885381.642390000    15.918  75.196  1024    2224
1102885382.212091000    12.793  87.012  1024    2224


Choose output filename describing the measurement you are doing, we'll use example.dat for example. Let it run with output redirected into a file this way for a couple of minutes:
bertest <arguments> > rx_1.dat

Running GNU R

Now run ./analyze example.dat (replace example.dat with your datafile name). and example.pdf will be generated.


Display the resulting Postscript or PDF and goto page 17. Read SNR for 5MHz and 10MHz at bottom line of the graph. Take the smaller of them as SNR.


Measure the distance d the light travels between RX and TX. Calculate NED as d*10^(SNR/20) where SNR is in dB.

An expected information missing here?