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: [email protected] > To: [email protected] > Subject: RE: Which Antenna? > Date: Wed, 15 Nov 2000 12:00:19 -0500 > MIME-Version: 1.0 > X-Resent-To: Multiple Recipients <[email protected]> > X-Listname: emc-pstc > X-Info: Help requests to [email protected] > X-Info: [Un]Subscribe requests to [email protected] > X-Moderator-Address: [email protected] > > > 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:[email protected]] > Sent: Wednesday, November 15, 2000 11:36 AM > To: [email protected] > 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: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Jim Bacher: [email protected] > Michael Garretson: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Jim Bacher: [email protected] > Michael Garretson: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
