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snip

Basically what you do is calibrate the instrument at the measurement
point, whether that point is the instrument connector or at the end of
a length of coax.

You attach an open, a short and a known resistance; 50 ohms by default
but it is user definable.

The instrument than frequency sweeps and stores the results in a user
definable calibration file.

When you make a measurement of an unknown, you define which calibration
file to use and the instrument corrects the readings to display the
characteristics at the measurement point.

Given that this is a $500 insturment and not a $20,000 labratory
instrument
there are going to be limits to how accurate all this is.

When I inspected antennas, we had two multi-kilobuck "Site Master"
instruments from Anritsu, mentioned here, that had a set of calibrated
terminations. IIRC, to calibrate the unit(s), we had to connect the
terminations, a short, a 50-ohm resistor and a shielded open circuit, one at
a time, to the instrument and tell it which one was connected. It swept the
frequencies of interest and stored its own baseline behavior over that band
of interest. Then, anything connected to it was referenced to that
baseline. We could also store a range of sweep frequencies (usually by the
name or type of antenna we intended to sweep) and it would recall all the
parameters. Automated, repeatable sweep testing is not available (yet) in
lower cost instruments.

I presume we could have calibrated any given cable, too. (Never required by
our test memos.)

Sal