Updated July 12,
here to go to our main page on microwave measurements
New for July 2010! Yet
another topic that has been missing too long in the Microwaves101
index, as recently pointed out by Poul-Henning.
TDR measurements provide a means
toward fault isolation in systems where transmission lines are inaccessible,
like buried fiber optic.
For now, we'll merely paste in
Poul's email and hopefully get back to creating content on this
I was quite amused by the
entry titled "Can you measure
Z0 with a ohmmeter?" and would like to point out that
such ohmmeters in fact do exist and have been commercially available
for almost 50 years.
Not only will these instruments
measure Zo of your cable, they will also neatly present the result
graphically as function of the distance along the cable.
Journal Sept. 1963 v15/n1
introduces the instrument and HP
Journal Feb. 1964 v15/n6 explains
in detail and with many illustrative examples how useful this
With a moderately good digital
scope, and a good sharp squarewave, readily available from many
members of the 74xx familiy, you can cook up your own TDR analyzer
in no time. This is also a great demonstration of the (nearly)
speed of light in coax cables.
I am actually surprised
that Google is unable to find a little smart TDR construction
for radioamateurs, it is an incredibly useful way to locate antenna
and cable trouble.
The standalone TDR analyzer
has been replaced today with professional network analyzers, which
will present a TDR view by transforming a frequency sweep to the
time domain with a FFT.
But in fibre optical transmission,
TDR-meters still rule: That is how you find out where the ship
or backhoe tore your fiber cable.