Grace, read the appendix 3 of the NPL paper. They state that " free-space antenna factor is appropriate for 3 m measurements". This is what we also use as it minimises the uncertainties from height scanning. Note that the free-space AF should not be used if you check your site NSA; there you need height-specific antenna factors. Regards, Ari Honkala
_____ From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of ext Grace Lin Sent: 29. helmikuuta 2008 4:29 To: Luke Turnbull Cc: emc-p...@ieee.org Subject: Re: Free Space Antenna Factor Dear John, Ken, Luke and others, Thank you so much for your comments. I printed out the document from the link Luke provided. I ran out of time in the office to read it. Please allow me to explain my question more detail. One of antennas I purchased came with free space antenna factors. According to ANSI C63.5: 2006, free space antenna factors are done at 10-meter distance. I will perform radiated emission measurement at 3-meter. Should I use the free space antenna factors without any calculation? Or, is there any equation to convert free space antenna factors for measurement distance other than 10-meter? The antenna vendor told me to use the free space antenna factors, then compare limit to 10-meter limits. I am not convinced to do so as this will have about 10 dB difference. To confirm my concern, I had a friend, who works at a well-known commercial lab and has the same model of the antenna, fax me his antenna factors at 3m and 10m. I list some data below for your reference. Free space antenna factors are from my antenna. 3m and 10m data are horizontal polarization. 30MHz-19.6 (3m), 18.7 (10m), 17.8 (free space) 40MHz-14.2 (3m), 13.7 (10m), 11.9 (free space) 50MHz-9.9 (3m), 9.1 (10m), 7.3 (free space) 60MHz-6.8 (3m), 7.1 (10m), 5.45 (free space) 70MHz-7.2 (3m), 7.3 (10m), 5.2 (free space) 80MHz-8.7 (3m), 7.4 (10m), 6.5 (free space) 90MHz-10.2 (3m), 9.4 (10m), 8.75 (free space) 100MHz-11.8 (3m), 11.3 (10m), 10.5 (free space) 200MHz-10.9 (3m), 10.3 (10m), 9 (free space) 300MHz-14.5 (3m), 13.2 (10m), 13 (free space) 400MHz-17.1 (3m), 16.2 (10m), 15.9 (free space) 500MHz-18.6 (3m), 17.5 (10m), 17.25 (free space) 600MHz-19.9 (3m), 18.6 (10m), 18.5 (free space) 700MHz-20.2 (3m), 18.8 (10m), 19.18 (free space) 800MHz-21.3 (3m), 19.9 (10m), 19.6 (free space) 900MHz-22.2 (3m), 20.8 (10m), 20.35 (free space) 1000MHz-22.9 (3m), 20.9 (10m), 20.9 (free space) >From the above data, I don't find any difference between 3m and 10m close to 10 dB. Thank you and look forward to your help. Best regards, Grace On 2/28/08, Luke Turnbull <luke.turnb...@trw.com> wrote: Grace, Have a look at the following guide from NPL, Page 41. (Sorry, you have to give them your name and address to download it). The correction is because the actual receiving element of a log-periodic may vary in distance between about 2.5 and 3.5m. The correction gives the field that would be at 3m distance from the product. http://publications.npl.co.uk/npl_web/pdf/mgpg4.pdf Good Luck, Luke Turnbull >>> "Grace Lin" <graceli...@gmail.com> 27 February 2008 18:48 >>> Dear Members, Could someone please teach me how to scale free space antenna factors for my 3-meter distance measurement? One antenna vendor told me that I could scale free space antenna factors. I couldn't reach this vendor at the moment. Thank you and look forward to hearing from you. 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