Regarding Cable Loss - RF Cafe Forums

 Post subject: Regarding Cable Loss

Posted: Thu Jun 16, 2005 11:40 pm 

Hi all,

I had a question regarding measuring cable loss, How to connect the equipments to calculate the cable loss from one end of the cable to another if you have a Signal Generator, Spectrum Analyser and Power meter. How should I connect the cable to and what are the parameters Should I change to know the cable loss.

Thanks in Advance!

Dreamer

 Post subject:

Posted: Fri Jun 24, 2005 11:15 am 

Greetings Dreamer:

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