Phase shift affect power readings? - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues - primarily having to spend time purging garbage posts from the board. At some point I might start the RF Cafe Forums again if the phpBB software gets better at filtering spam.

Below are the old forum threads, including responses to the original posts.

-- Amateur Radio
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews

-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

Sergio Chavez

Post subject: Phase shift affect power readings?

Posted: Fri Jan 25, 2008 6:42 pm

Lieutenant

Joined: Thu Jan 24, 2008 4:29 pm
Posts: 2

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

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 406
Location: Germany

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!

Sergio Chavez

Post subject:

Posted: Mon Jan 28, 2008 1:01 pm

Lieutenant

Joined: Thu Jan 24, 2008 4:29 pm
Posts: 2

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

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 406
Location: Germany

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!!

Jeanalmira

Post subject:

Posted: Tue Jan 29, 2008 4:30 am

General

Joined: Tue Mar 15, 2005 11:43 pm
Posts: 67
Location: Singapore

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

Posted 11/12/2012

Webmaster:

Kirt Blattenberger,

BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website: AirplanesAndRockets.com

My Daughter's Website: EquineKingdom