You cannot rely on manufacturer’s specs on amplifier harmonic output unless you are operating at power levels they specify. At and above the power output they specify, harmonic amplitudes increase much faster than power output. The lesson here is to buy enough amplifier that the linear range provides the full power you need. That is very expensive. Ken Javor
Phone: (256) 650-5261 ________________________________ From: "ce-test, qualified testing bv - Gert Gremmen" <g.grem...@cetest.nl> List-Post: emc-pstc@listserv.ieee.org List-Post: emc-pstc@listserv.ieee.org List-Post: emc-pstc@listserv.ieee.org Date: Mon, 2 Nov 2009 16:40:01 +0100 To: "Pawson, James" <james.paw...@echostar.com>, <EMC-PSTC@LISTSERV.IEEE.ORG> Conversation: [PSES] 61000-4-3 and 61000-4-20 Field Uniformity Requirements Subject: RE: [PSES] 61000-4-3 and 61000-4-20 Field Uniformity Requirements Some numbers to help: Say if your power amplifier (@40 Mhz) had a third harmonics of -6 dB compared to the ground wave, and the antenna gain would be 0 dB at 40 Mhz, and +10 dB at 120 MHz, then the 3rd harmonic would exceed the ground wave with 4 dB ! So you can measure the problem in the directional coupler, if you add the antenna gain (+ cable losses + coupler losses) per frequency to the values measured. Beware that couplers have frequency dependent behavious also. BTW most solid state amplifiers have at least -20 dB of distortion within the specified power limits, so the problem won’t show up frequently. But with the (older) TWT amplifiers that was entirely different. Harmonics at -3 dB were not uncommon. Regards, Ing. Gert Gremmen g.grem...@cetest.nl <mailto:g.grem...@cetest.nl> <mailto:g.grem...@cetest.nl> www.cetest.nl <www.cetest.nl> Kiotoweg 363 3047 BG Rotterdam T 31(0)104152426 F 31(0)104154953 Before printing, think about the environment. Van: emc-p...@ieee.org [mailto:emc-p...@ieee.org] Namens Pawson, James Verzonden: Monday, November 02, 2009 4:05 PM Aan: EMC-PSTC@LISTSERV.IEEE.ORG Onderwerp: RE: [PSES] 61000-4-3 and 61000-4-20 Field Uniformity Requirements Hi Ken, thanks for the reply. So if one was to measure the output from the power amplifier into the test chamber (with a directional coupler and spectrum analyser say) and observed the harmonics, then that would that tell you if you had excessive harmonics or would that be a feature of the transmitting antenna and would only be measurable in the chamber itself? Also, would that apply to a GTEM? I would have thought a GTEM would be fairly efficient at low frequencies. Thanks, James ________________________________ From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: 02 November 2009 13:52 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] 61000-4-3 and 61000-4-20 Field Uniformity Requirements Your point number 2 is necessary because the field-sensing devices are broadband and if a signal harmonic is higher than the fundamental, the field sensor can’t tell the difference and the field will be leveled on the harmonic amplitude, not that of the fundamental. Thus you have not the case of an over-test, but an under test at the fundamental. This problem is the reason (my assumption) why 61000-4-3 starts at 80 MHz; the biconical antenna below 80 MHz becomes progressively less efficient and it is very easy to have second and third harmonics of signals below 80 MHz radiate at higher levels than does the fundamental. The actual 6 dB number is something of a traditional limit; with a broadband device performing an rss of everything in its bandwidth, a signal 6 dB under the fundamental will increase the overall measured level by 1 dB, so that you are under-testing at the fundamental by 1 dB if a spurious signal 6 dB below the fundamental is included in the mix. Ken Javor Phone: (256) 650-5261 ________________________________ From: "Pawson, James" <james.paw...@echostar.com> List-Post: emc-pstc@listserv.ieee.org List-Post: emc-pstc@listserv.ieee.org List-Post: emc-pstc@listserv.ieee.org Date: Mon, 2 Nov 2009 11:03:12 -0000 To: <emc-p...@ieee.org> Conversation: 61000-4-3 and 61000-4-20 Field Uniformity Requirements Subject: 61000-4-3 and 61000-4-20 Field Uniformity Requirements Hi, As far as I can tell, the requirements for field uniformity in 61000-4-3 and 61000-4-20 are the same. Primary field components within 6dB (after discarding 25% with the biggest deviation) and of these remaining points no secondary field components greater than 6dB of the primary. 1) Is there an issue if the secondary components were higher than 6dB of the primary? Even if the EUT was tested in multiple orientations? As far as I can see, it would result in an over test of the EUT and isn't compliant with the standards, but more importantly would testing like this mask an issue that would only occur if the field was primarily polarised in one direction? e.g. a slot orientation forming an antenna? Provided the EUT was rotated and the field component was high enough so this situation occurred, do we care that much about the secondary components? 2) Another scenario: what if due to some kind of resonance in the test facility the primary field component couldn't be achieved without overloading the amplifier, but the isotropic field (square root of the sum of the sqaures of the X, Y and Z components) was of the right level. That doesn't feel right because of the questions I outlined above. 3) Also the standard calls for the front face of the EUT to be "initially placed with one face coincident with the calibration plane" (61000-4-3, clause 8.2). Why the front face? Why not the central plane of the EUT? Do we not care what happens 'after' the calibration plane? Does anyone have any thoughts / experience that they could share on these points? Thanks in advance James James Pawson Leading Hardware Engineer EchoStar Europe T: +44 (0)1535 659000 e: james.paw...@echostar.com - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. 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