Power Loss Measurements in Feeder

You can always measure power loss in two separate steps, but you have to make sure your equipment is working at the very same load condition. If you can assure this, so you can. If your load varies and you cannot stablish at least an average power consumption, than an instant power measurement and comparison may give you better indications. But if it varies a lot, I think even with simultaneous measurement it will be hard to tell...

From Sleepy,

A precise method of understanding losses in feeders is to measure the VSWR or Return Loss of the feeder at it's input.

Unfortunately this is not the whole story as you will need to understand the loss cause by the impedance mismatch at the source; Can you measure the source impedance?

I once had great fun measuring the Rieke diagram of a Reflex Klystron, which showed the frequency and power output of the klystron against load impedance. The theory of Klystrons and Magentrons shows that they oscillate when the output impedance is the conjugate of the load.

If the source is something more tractable then the method above works.

Reverting to your question:

You can measure power at both ends simultaneously using accurately calibrated directionally couplers. This ought to be more accurate than measuring separately at both ends as the power measurements will depend on source impedances.

Ultimately I asume that you are interested only in the exit power from the feeder to the load. Presumably an antenna. But beware again the the delivered power will depend upon the load impedance. All of the above depend upon the frequency of operation and the frequency of measurement.

High Power levels sometimes cause problems that are not easily forseeable.

Have fun

Sleepy

Thanks a lot for the reply.The power has to be meaured at one end is a generator 18.5MW and other end is a transformer.Voltage 6.6KV freq 50Hz.Need to carry measueremnts to findthe losses in the cable.I would be grateful if u can provide some references as my search in google has not produced the required results.

Thanks again

Hi,

My comments were all aimed at high frequencies, 50 MHz to 50GHz.

I have almost no expertise on Power measurements at 50HZ.

Sorry for any confusion, I guess that it pays for all of us to be as careful as possible when phrasing questions and answers.

We knew what me meant! And we knew the constraints of our questions and answers; we just need to tell someone!!

Sleepy