I was not at the convention so did not see the biconical antenna presentation. I will make it a point to look for a copy of the paper and read it.
I disagree that vertical antenna factors should be used to remove the "surface wave" from the measurement. Site attenuation measurements are intended to measure the propagation of a signal over a test site ground plane. If the "surface wave" is a component of the propagation being measured than it cannot be removed from the result and still yield a valid measurement. I am not entirely sure what it is that you are referring to as the "surface wave". As a wave propagates over a ground plane there are two signal paths, a direct wave between the source and receiving antenna and a wave that reflects off the ground plane to the antenna. I suspect the reflected wave is what you are referring to as the "surface wave". What distance are you making you measurements at? Are you calibrating your antennas in a semi anarchic chamber or performing site attenuation measurements on the chamber? I am interested in continuing this discussion but will be out of the office until after Labor Day, at which time I will respond to any further dialog. Tom Donnelly EMC Engineer Lucent Technologies ************************************************************************************************************** Original message: Tom, Did you get to the presentation about getting the most out of a biconical antenna? Some thoughts contained there on antenna calibration, too. I found some time ago that using antennas does lead to the kind of mutual coupling Martin talked about, and also -- and this is not mentioned much -- even with small sources, there is a definite surface wave near the ground plane at 30-35 or 40 MHz. This skews reading upwards, but as it is part of the site propagation, I think it has to be factored out by doing that vertical antenna factor measurement. A couple more meters, and the surface wave is no longer a problem. I say surface wave, because I don't think this is a mutual coupling problem. Even small sources seem to generate it. I am presently working on an antenna calibration for a semi-anechoic chamber in which I shall be able to investigate this more closely. Regards, Cortland
