A home-made time domain reflectometer saves the day for engineers working half-way between the Arctic Circle and the North Pole
While working with a team of engineers in Northern Greenland, we suspected that a long outdoor run of
coax had malfunctioned.
I went to the equipment locker to get the TDR (Time Domain Reflectometer)
only to find that it was out for calibration. TDR’s are
a type of oscilloscope that allows you to determine coax quality and
the distance to any anomalies. They do this by monitoring the
reflection of the rising or falling edge of a square wave. Knowing how
a TDR worked, I quickly assembled a square wave generator and
oscilloscope to make my own TDR but we didn’t have any reference for
time vs. distance.
Something the TDR will do when you select the proper coax parameters.
We called the supply depot asking for a spool of the coax and found
that they had a 1000 ft. spool that had not yet been cut. We took the
rigged “TDR” to the supply room and tested it to create a time vs.
distance correlation. We then took the “TDR” to the transmitter and
connected it to the suspected coax. Sure enough, there was an open at
about 6500 ft. and we were able to quickly find a connection between
two sections that had come apart. We fixed it and were back online in a
matter of just a few hours.
Had I not rigged the “TDR” we would have had to walk over two miles
outside in the dark in sub-zero temperatures looking for the problem.
Author Robert Bachellor
is a product engineer.