# Regarding Cable Loss - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Dreamer
Post subject: Regarding Cable Loss
Unread postPosted: Thu Jun 16, 2005 11:38 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.

Dreamer

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Guest
Post subject: Cable Loss Measurement
Unread postPosted: Fri Jun 17, 2005 1:26 pm

Assuming you've got cable and equipment with the same impedances (usually 50 Ohms):

1. Measure output of signal generator with power meter
2. Insert significant length of cable between signal generator and power meter.
3. Measure output from cable
4. a. Cable loss (dB) = dBm(gen) - dBm(cable output)
b. Cable loss (fraction) = Pout(cable)/Pout(gen) powers in W, mw, etc.

Note that some power meters require external termination - you will, of course, have to provide that.

An important point is that the terminating impedance must be equal to the characteristic impedance of the line for this simple method to work.

Remember that cable loss is a function of frequency, so measure at the frequency or frequencies that you're interested in.

Good luck.

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Dreamer
Post subject: Regarding Cable Loss
Unread postPosted: Fri Jun 17, 2005 1:45 pm

Thank you very much,

Both impedances are at 50 ohms also you have told to measure signal generator with power meter, so mean just input some power from gen into meter and check the reading on the power meter? for that frequency.

Thanks,

Dreamer.

Posted  11/12/2012

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