For a tuned dipole the AF will be within 1 dB at distances of 3 and 10 meters above 100 MHz. Below 100 MHz, and at a distance of 3 meters, the distance in wavelengths falls below 1 wavelength. The AF is then lower at 3 meters at the lower frequencies.
I don't think that a biconical is as sensitive as a tuned dipole (below 50 MHz, anyway). And with a log periodic the phase center moves with frequency thereby causing a difference between the 3 and 10 meter AF. The manual for your antenna should have an AF graph with both 3 and 10 meters. Dave Cuthbert Micron Technology From: [email protected] [mailto:[email protected]] On Behalf Of Wan Juang Foo Sent: Wednesday, April 21, 2004 2:32 AM To: [email protected]; [email protected] Subject: Re: Measurement distance and antenna factor Hi, Whatever the measurement distance, 3 m or 10 m each will have a different set of antenna factors (mostly less than 0.5 dB difference) for any given antenna. Ken Javor <[email protected]> wrote on 21/04/2004 03:52 PM > If the antenna factor is measured in the far field, whether that be > either 3 or 10 meters, then it will not change if you measure it at > a larger distance. But if the antenna factor is measured in the Agreed only if the antenna is calibrated in free space condition. I presume free space is x>>lambda/2pi > near field, whether at 3 or 10 meters, then it will change at any > other separation. A near field 'antenna' in the very near field is nothing but a E or H field 'probe'. AFAIK, Antenna Factors for any antenna calibrated in the 'far-field' are also know to be slightly dependant the height of (the 'measurement antenna') used during the calibration (above the ground plane). Off the cuff, I can recall that there was a paper on this some years ago. Can anyone recall the title and details? Tim Foo 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 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
