Michael, Note that Brian has a bidirectional coupler and checks power in both directions. Checking power in both directions is a very good indicator that things are as they were when the field was calibrated (when the original forward and reverse power readings were made), even indicating that the antenna is radiating as well (or as poorly) as it did when the field was calibrated. The reflected power is especially sensitive to the condition of the coax cables and antenna. The only thing I think of that a bidirectional power check would not catch (that the field measurement would catch) is an improperly aimed antenna. A quick eyeball check should catch that problem.
As a practical matter, forward power alone is usually sufficient to catch typical gross problems (coax cable broken or not connected). My canned test software checks forward power and compares it to the forward power measured during field calibration. I never have had the power check allow the test to progress more than a handful of frequency steps when there was an open coax cable. The high reverse power reflects off of the imperfect output SWR of the power amplifier. This power that reflects off the power amplifier output adds to or subtracts from the forward power at certain frequencies sufficiently that the forward power is driven out of error limits I set. Donald Borowski Schweitzer Engineering Labs Pullman, WA, USA From: "Sundstrom, Michael" <[email protected]> To: "Kunde, Brian" <[email protected]>, "[email protected]" <[email protected]> List-Post: [email protected] Date: 09/28/2011 07:42 AM Subject: RE: BS EN61000-4-3 and calibrated fields. Sent by: [email protected] Hello all, I.E. forward power: That will only tell you if you have power going down the coax. Not if it is actually being radiated. The probe in the field will tell you that all is working, the calibration file will set your levels. Michael Sundstrom OHD / TREQ Dallas Electronic Lab Analyst, EMC Lead 2170 French Settlement Rd, Suite B Dallas, Texas 75212 (214) 579 6312 (940) 390 3644c KB5UKT Albert Einstein once said, "The definition of insanity is doing the same thing over and over again and expecting different results". From: Kunde, Brian [mailto:[email protected]] Sent: Wednesday, September 28, 2011 7:43 AM To: [email protected] Subject: Re: [PSES] BS EN61000-4-3 and calibrated fields. Can?t you measure Forward Power via a power meter and bi-directional coupler and compare it to your calibration data as a sanity check? We actually do a quick check test prior to running an official test by measuring forward and reverse power with modulation turned OFF at 10% frequency points. We compare the data with our calibration data and calculate the amp wattage output and SWR. So if the antenna or cable was going bad this pre-test would find it without messing with the field probe. From: [email protected] [mailto:[email protected]] On Behalf Of Gärdin Petter Sent: Wednesday, September 28, 2011 5:55 AM To: Bryce Stammerjohan; [email protected] Subject: RE: BS EN61000-4-3 and calibrated fields. And anyone not having a field probe present during test should need a personal sanity check. How would you make sure you really have a field and not a broken antenna or something else. As per 17025 you need to make sure that you know what you are doing. Petter From: Bryce Stammerjohan [mailto:[email protected]] Sent: den 27 september 2011 22:19 To: [email protected] Subject: Re: [PSES] BS EN61000-4-3 and calibrated fields. I asked this just a few days ago when at a lab ? this particular tech said it was a ?sanity check?. The displayed 3-axis RMS value was close to the V/m setting I requested, but did vary with frequency and polarity, unsurprisingly. Bryce From: Kunde, Brian [mailto:[email protected]] Sent: Tuesday, September 27, 2011 1:19 PM To: [email protected] Subject: Re: [PSES] BS EN61000-4-3 and calibrated fields. Not to hijack this thread, but why do some test labs setup the Field Probe in the chamber next to the EUT during the test? The measurement with the EUT in the field should be all over the place and would have little value. Am I missing something or are some labs leveling off the Field Probe during testing? From: [email protected] [mailto:[email protected]] On Behalf Of Ian White (UK) Sent: Tuesday, September 27, 2011 6:00 AM To: IEEE Forum ([email protected]) Subject: BS EN61000-4-3 and calibrated fields. Could you please help: Could you explain what is the correct procedure when using an anechoic chamber which is calibrated and operating to EN61000-4-3. During calibration of the chamber, a calibration file is made and it is assessed according to the guidelines laid down under BS EN61000-4-3. During calibration the chamber is empty. During a normal test run a UUT is put into the chamber. The questions is : a) Do you use the calibration file as the starting point and adjust the field strength which may have changed due to the UUT being in the chamber. b) Just take the calibration file and run it and except the filed strengths would have changed due to the UUT being in the chamber. Thanks Ian White Compliance and Reliability. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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