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 measure directly.
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 measurement.
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