I still use a home made TDR (time domain reflectometer) for testing
cables. Old habits and methods die slowly.

Do you have any construction information available for your TDR?

You can do this with a function generator (fast-edge square-wave
pulses are what you want), possibly a resistive pad, a T connector,
and a fast oscilloscope. I used this approach to test out and
identify some poorly-labeled ham radio antenna cables at my city's EOC
a couple of years ago.

Connect a BNC "T" junction to the oscilloscope's vertical input. To
one side of the "T", connect a coax to a function/pulse generator that
has a 50-ohm output (or use a low-Z generator and a 50-ohm series
resistor pad). To the other side of the "T", connect the coax you
want to test. Set the o'scope vertical sensitivity so that it covers
3-4 times the step voltage of the generator, and set the horizontal
sweep rate to cover 2-3x the length of the coax you want to probe
(figure 1 nanosecond per foot as a starting value, and triple it).
Set the function/pulse generator for pulses that are at least twice
the sweep length, and (if it's a pulse generator) a reasonable
repetition rate (1 kHz or so). Set the scope for DC coupling, and set
it to trigger on the rising edge of the pulse.

If the far end of the coax is open, and the coax is in good shape,
what you should see during the sweep is an initial abrupt rise (to the
generator's nominal output voltage), a flat trace for 2x the cable's
end-to-end propagation time, and then an abrupt rise to twice the
generator's nominal outut voltage.

If you terminate the coax in its characteristic impedance, the second
rise won't occur (or you'll see just a tiny discontinuity at that
point, if the termination resistor isn't an exact match). If you
short the far end of the coax, the second rise will be replaced by an
abrupt dive down back to zero.

Any wiggles or bumps in the first part of the trace (between the
initial rise, and the reflection) will be the result of impedance
discontinuities in the cable... damage, bends, connectors, conductor
migration, etc. Measure the time delay between start-of-trace and
wiggle, apply the cable's propagation-speed factor, and you can tell
how far down the cable the discontinuity lies.

If you have a scope with dual sweep speeds and a sweep delay, you can
"zoom in" on interesting sections of the trace and look at them in
more detail.

If you don't want to lug a big pulse generator around with you, you
can build a small one which connects right onto the front of your
o'scope. A 555 driving a fast Schmitt-trigger inverter, a PIC with a
fast discrete output-driver circuit... there are probably about a
zillion circuits which would give a fast 50-ohm pulse that would work.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!