>> Can you please explain why? The receiving antenna just responds to the field strength at its position; it doesn't 'know' anything about the source - it cold be an EUT at 10 m or a distant TV transmitter or even a cosmic source. <<
This isn't the issue. The receiving antenna, as you say, can't tell. The problem is the substitute antenna. We assume the source is a dipole (or, here, a bilog) at every frequency. Our substitute antenna has a simple pattern (even a bilog - we spend a lot of money to get it, too). The source is not so simple. Even if it IS a half-wave dipole at (say) 100 MHz, at harmonics it is a wavelength long or more, and radiates in sheaves of cones oriented at some angle along the axis of the wire (a LP does NOT do this!) - most of which may miss the receiving antenna completely on an OATS. The angles along the wire decrease as the frequency increases. It will have gain over a dipole; the lobes off its ends narrower and stronger than those from a dipole fed with the same power, and at high enough harmonics, close enough to the axis of the conductor that they are again directed towards the receiving antenna as we turn the EUT. This will bias calculations which assume the source has a simple pattern at _every_ frequency. It doesn't. Cheers! Cortland ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ 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: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
