Thanks for your response. Since our lab will be used for pre-compliance in an R&D facility, I foresee several engineers wanting to use the equipment. I would hate to see someone drop an antenna or knock one off the wall that isn't being used. I didn't think of the scenario you mentioned where an unused antenna is left in the room but I can definitely see that happening.
As for the standard, I have referred to a preliminary standard from BSI. Its document number is 96/216005. The title is "CONCEPT EMC STANDARD ANECHOIC CHAMBERS: PART X: EMISSION MEASUREMENTS IN FULLY ANECHOIC CHAMBERS. I ordered it from Global for about $35. One of the interesting things in the standard is that instead of calculating the absence of reflected signal from the ground plane, it recommends a 6dB fudge factor. The reasons we are building a FAR chamber is that you don't have to raise and lower the antenna to compensate for reflected signal from the metallic ground plane. Also, theoretically, you get a much better correlation to a 10-m OATS than you do with a 3-m SAR. There was a very good article on FAR chambers in the May/June issue of Compliance Engineering magazine entitled "Examining the Use of Fully Anechoic Rooms for Full-Compliance EMC Testing". -----Original Message----- From: eric.lif...@ni.com [mailto:eric.lif...@ni.com] Sent: Wednesday, November 15, 2000 1:41 PM To: Tudor, Allen Subject: Re: Which Antenna? Allen, Use the biconolog. When I hear people knock it I reply with - how much wear on the N connectors can the antenna and cable take before it's a bigger factor? Also, each time a bicon and log antenna is changed on the mast or tripod, you take a risk of an accident that renders the antenna clearly out of calibration; you could be shut down for weeks unless you can afford a spare set of antennas. Also, people tend to rush things and will leave the unused antenna sitting on the pad during a test, almost directly under the antenna in use! I've seen this at an accredited test lab. That alone introduces error. Our chamber is just a semi-anechoic 3 meter box and uses the same biconolog as our OATS does. When I justified the purchase, I added a 3rd biconolog to the order as a spare. The spare also acts as a 3rd identical antenna so we could self-cal the antennas, and it lets us run NSA checks on the OATS without shutting down the chamber. We're thinking of adapting our 3 meter chamber for the new fully anechoic (FAR) test method, but is the new test standard published yet? Is that why you are buidling a FAR? Best Regards, Eric Lifsey Compliance Manager National Instruments Please respond to "Tudor, Allen" <allen_tu...@pairgain.com> Sent by: owner-emc-p...@ieee.org To: emc-p...@ieee.org cc: Subject: Which Antenna? Greetings, I am having a fully anechoic pre-compliance test chamber built. By fully anechoic, I mean ferrite tiles will be installed on the floor as well as the walls and ceiling. The inner dimensions of the chamber will be 24 feet long by 14 feet wide by 13 feet high. The chamber will be used for radiated emissions as well as radiated immunity. Radiated emissions testing will be from 30MHz to 1GHz. I am looking at a biconilog antenna that can be used for emissions and immunity testing. However; for emissions measurements, the salesman recommends that I use separate biconical and log-periodic antennas. He says that if I use the biconilog antenna for emissions measurements, there will be some coupling to the ground plane when the antenna is in the vertical position. However, this chamber will have ferrite on the floor, so I don't know if that is a valid argument. Aside from the expense of two additional antennas, I have two conflicting concerns. 1. I would rather not have to work with more than one antenna if I don't have to due to down time and possible damage to an antenna. 2. On the flip side, I want to make sure that I have repeatable results, especially at the low end of the spectrum. Any advice would be greatly appreciated. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
