Phase shift affect power readings? - RF Cafe Forums

 Post subject: Phase shift affect power readings?

Posted: Fri Jan 25, 2008 6:42 pm 

Hello all, this is Sergio Chavez, I work as a test engineer and I was recently assigned to work in a RF product, this is a motorola two way radio.

I don't have too much RF experience and I'm looking for help understanding how a phase shift can cause bad power readings.

Someone in the group knows a book or site where I can find information
how the phase affect the reading?
I have a Network Analyzer (Agilent E5062a) and I can read the phase but I don't know if a 10 or 20 degrees affects the power readings.
a phase shift of 10 degrees, how much power can loss?

any help will be appreciate

thanks
sergio

_________________
Serch

 Post subject:

Posted: Sat Jan 26, 2008 2:02 pm 

Hello Sergio,

To measure the output power you should use RF Power Meter. VNA is usually not used for power measurements.

When you use RF Power Meter, phase shift should not affect your RF power reading. RF Power Meter does a scalar measurement. The sensor of the power meter reads the average level of the power by integrating the measured RF power over a given period of time.

Hope this helps!

 Post subject:

Posted: Mon Jan 28, 2008 1:01 pm 

Thanks IR for your help.

we are using a power meter (agilent 437B) to measure power.

I mention de VNA just to let you know that I found that testers have different phase, the phase shift is different between testers 10 or 20 degrees. we also read the return loss and we don't see too much different between testers.

I was wondering if different phase shift between testers could be the reason that we are getting different power readings.

Your explication about how the sensor and power meter works help me to understand that the phase shift does not affect the power readings.
I think I have to read more how the sensor and power meter works.

thanks again for your help
sergio

_________________
Serch

 Post subject:

Posted: Mon Jan 28, 2008 1:17 pm 

Hello Sergio,

You are welcome!

More about RF power meter and sensors you can find here:

http://www.radio-electronics.com/info/t ... logies.php

http://archive.evaluationengineering.co ... meters.htm

Enjoy!!

 Post subject:

Posted: Tue Jan 29, 2008 4:30 am 

Hi Sergio,

Just want to add a little bit on the above information. I think power sensor calibration might be the issue when experience different reading. Cal factor, frequency setting, offset, zeroing play important role in power reading accuracy.

I hope it helps.

Regards,

Jean Almira