If all you need to measure
is the loss of the cable, then all you need is the
spectrum analyzer (SA)* and, if both ends of the
cable cannot reach the SA from the same place, a
signal generator (SG).
* If the SA has a
generator output built in.
If both ends of
the cable can reach the SA and it has a built-in
generator, then simply calibrate the SA and place
the two cable ends between the In/Out ports and
Otherwise, measure the
output of the signal generator and either se tthe
S/A to give a relative measurement from there, or
note the power level to do the math yourself. Then,
connect one end of the cable to the SA input and
the other to the SG.
A good thing to do is
place an attenuator (at least 3 dB, preferably 10
dB) at the output of the SG both when taking a reference
reading and when connection the SG to the cable.
Doing so helps minimize any error that might be
caused due to impedance mismatch between the SG
and the cable. When measuring down to tenths of
a dB, it can make a noticeable difference in the
In both cases, be sure that
the SG is injecting enough power that the SA can
measure easily after passing through the attenuator
and cable loss.
- Kirt Blattenberger