Hi Dave, The point was that for lower frequencies NEVER such an optimum or best height can be found within the 1-4 meter range ! Make such a run between 30 and 150 MHz for HOR polarization only and you will see what I mean. If you use a dipole as receive and transmit (DUT) antenna the effect will be quite clear. Using a real life EUT will obfuscate it....
Gert Gremmen ce-test, qualified testing From: [email protected] [mailto:[email protected]] Sent: maandag 22 maart 2004 21:14 To: [email protected]; [email protected]; [email protected] Subject: RE: What is wrong in my 3 meters FAC measurement To get around the error of assuming point sources one can use a simulation such as NEC. The receive antenna can be simple to model especially if it is a tuned dipole. The DUT "antenna" is more difficult but I believe it can be modeled as a short dipole. Using this one can find the best heights of the RX antenna and compare a 3 meter to a 10 meter measurement. Give me some more info and I'll run this for you. Info needed: Receive antenna type Polarization I'll cut and paste the results into a word document that anyone here can have copy of. Shouldn't take too long to do. Dave Cuthbert Micron Technology From: [email protected] [mailto:[email protected]] On Behalf Of Ing. Gert Gremmen Sent: Monday, March 22, 2004 4:06 AM To: John Woodgate; [email protected] Subject: RE: What is wrong in my 3 meters FAC measurement John, You are right, isotropic was what I meant. To be computable, an antenna needs to be infinitely small because of the following reason: - a distance between an EUT and an antenna can be defined only accurate when both sizes can be neglected compared to the measuring distance. Both antenna's and EUT's in real life don't have a single point of reception resp. emission, so waves of multiple distances and multiple angles of incident will add together in creating a mesurement result. In addition, the measurement distance is in the same order of magnitude as both size of antenna and EUT. For an antenna to have any other characteristic then omnidirectional, it must have substantial size compared to wavelength. As the size must be small in my explanation it implicates the omnidirectional requirement. As an EUT is basically a transmit antenna of unknown configuration the same demands apply as for the receive antenna for a computable system to deliver accurate results. Of course, compared to the allover accuracy of EMI measurements a reasonable accurate result may be estimated using maths, but then surprises may be expected in single measurements. I showed in the explanation below that the blindness of an OATS is a math problem that exists for point transmitters and receivers only, and that the effect is less prone for real life measurements. However, in some test setups, this theoretical set up may be very well approximated, thereby reproducing this effect and creating surpises in correlations. Regards, Gert Gremmen Approvals manager ====================================================== ce-test, qualified testing Member of EMC committee CENELEC/IEC + Independent Consultancy Services + Compliance Testing and Design for CE + Improvement of product quality and reliability + Testing services according to: Electro magnetic Compatibility 89/336/EC Electrical Safety 73/23/EC Medical Devices 93/42/EC Radio & Telecommunication Terminal equipment 99/5/EC Website: www.cetest.nl (english) www.ce-test.nl (dutch) Phone : +31 10 415 24 26 Fax : +31 10 415 49 53 ====================================================== From: [email protected] [mailto:[email protected]]On Behalf Of John Woodgate Sent: Monday, March 22, 2004 10:59 AM To: [email protected] Subject: Re: What is wrong in my 3 meters FAC measurement I read in !emc-pstc that Gert Gremmen <[email protected]> wrote (in <[email protected]>) about 'What is wrong in my 3 meters FAC measurement' on Sun, 21 Mar 2004: >I hope I made clear that FAR and OATS measurements cannot be compared at >all, but for strictly theoretical isotope receivers and transmitters >that behave as single points. I agree with the substance of your explanation, but I am puzzled by the word 'isotope', which is undoubtedly not the intended word. I thought about 'isotropic', but that is not usually applied to receivers ('omnidirectional'), and it isn't strictly necessary for the receiver to be omnidirectional for the comparison to be computable: it only needs to have a beamwidth great enough to accommodate the rather simple pattern of emissions from the point-source transmitter and reflections from the ground-plane. A cardioid directional response, for example, appears satisfactory. -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
