RE: Which Antenna?
Allen, We have used a biconilog for radiated emissions testing in our 3m semi-anechoic chamber for the past three years. We have done extensive correlation studies to the biconicals we own and found there to be little issue with using the biconilog. Its well balanced and therefore, we're not seeing an issue with coupling to the ground plane. You may recall in years past, when baluns weren't as well balanced as most are today, antenna manufacturers would tag the ground side of an antenna so you could point that side down in a vertical measurement. I've found that to be unnecessary with our biconilog. On the other hand, I'm merely an EMC engineer and not an antenna designer and therefore I can only share our experiences. That being said, I'll buy another biconilog if I build a second chamber. Don Rhodes Principal EMC Engineer 503.685.8588 voice 503.685.7256 fax don.rho...@infocus.com -Original Message- From: Tudor, Allen [mailto:allen_tu...@pairgain.com] Sent: Wednesday, November 15, 2000 8:36 AM To: emc-p...@ieee.org 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
RE: Which Antenna?
All, I didn't get out a tape measure, but I believe a bilog antenna is taller than a bicon antenna in the vertical polarity, and would be closer to the floor at the minimum antenna height of 1 m (for most test procedures.) For that reason, I believe there would be more coupling to the ground plane from a bilog than a bicon. However, since you have ferrite on the floor, there should be less coupling to the ground plane. If you had cones on the floor, too, I believe there would be even less coupling at the lower frequencies (near 30 MHz,) where the coupling effect is more pronounced. For emissions testing, I believe the FCC still lets you pretend that you are using a dipole antenna a minimum of 10 cm (?) off the floor when determining the minimum antenna height for vertical measurements. (For example, lamda/4 + 0.1 m = 2.6 meters minimum height at 30 MHz.) It's been a while since I set up a tuned dipole for a 30 MHz measurement, but if this FCC rule is still valid, the differences between bilog and bicon coupling effects at 2.6 m height would be minimal. Regards, Dan From: wo...@sensormatic.com To: emc-p...@ieee.org Subject: RE: Which Antenna? Date: Wed, 15 Nov 2000 12:00:19 -0500 MIME-Version: 1.0 X-Resent-To: Multiple Recipients emc-p...@majordomo.ieee.org X-Listname: emc-pstc X-Info: Help requests to emc-pstc-requ...@majordomo.ieee.org X-Info: [Un]Subscribe requests to majord...@majordomo.ieee.org X-Moderator-Address: emc-pstc-appro...@majordomo.ieee.org For emissions testing, the antenna should have a well balanced design when used over a ground plane. Perhaps the antenna you are considering is not well balanced. The balance issue shows up in the vertical orientation when there is coupling to the ground plane and is not unusual in some bicons. I am assuming that you will install a removable ground plan for FCC and ETSI emissions measurements. Richard Woods -- From: Tudor, Allen [SMTP:allen_tu...@pairgain.com] Sent: Wednesday, November 15, 2000 11:36 AM To: emc-p...@ieee.org 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 --- 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
RE: Which Antenna?
Thanks for your response. Since our lab will be used for pre-compliance in an RD 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
Re: Which Antenna?
Mr. Allen, I have had some experience with biconilog, log periodic, and biconical antennas for both emissions and immunity testing. I never had any issues with the biconilog when used for immunity testing. However, after using the biconilog for emissions testing on a 3 meter OATS, I went back to seperate antennas. I found that the discreet antennas offered better loss factors and a more linear calibration plot. I also found the biconilog to be VERY directional. This made it more difficult and tedious to ensure repeatable measurements with the biconilog. Just my 2 cents. Regards, Randy Flinders EMC Engineer Emulex Corporation randall.flind...@emulex.com aka Chairman Orange County Chapter IEEE EMC Society r.flind...@ieee.org Tudor, Allen wrote: 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
RE: Which Antenna?
Allen, We have a similar chamber with similar issues. We use the immunity chamber as a precompliance emissions chamber also. It's a lot of work to remove the tiles from the floor so we left them in place for precompliance emissions investigations. We use a biconilog antenna for both emissions and immunity. We have found that our correlation factor to our OATS is roughly +/- 8 dB. This works for us as the chamber eliminates the radio and TV ambients and we can see the entire profile at a glance. We now do 90% of our emissions mitigation in the chamber and then final compliance measurements at the OATS. Hope this insight helps. Don Umbdenstock Sensormatic -- From: Tudor, Allen[SMTP:allen_tu...@pairgain.com] Reply To: Tudor, Allen Sent: Wednesday, November 15, 2000 11:36 AM To: emc-p...@ieee.org 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
RE: Which Antenna?
For emissions testing, the antenna should have a well balanced design when used over a ground plane. Perhaps the antenna you are considering is not well balanced. The balance issue shows up in the vertical orientation when there is coupling to the ground plane and is not unusual in some bicons. I am assuming that you will install a removable ground plan for FCC and ETSI emissions measurements. Richard Woods -- From: Tudor, Allen [SMTP:allen_tu...@pairgain.com] Sent: Wednesday, November 15, 2000 11:36 AM To: emc-p...@ieee.org 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
