Its a fool's errand to use only antenna modelling software to evaluate the complexity of topband transmitting antenna performance.
Why is that? Antenna models do not take into account polarization mismatch loss, a fact of life because the electron gyrofrequency is so close to 160 meters. See K9LA's excellent article: https://k9la.us/Polarization.pdf Antenna models also do not consider the lossy ground reflection in the Fresnel zone in front of the antenna. The Fresnel zone isn't a thin line along the ground in the direction of the distant receiving antenna, rather it has an elliptical shape with significant width. That's why HFTA analysis should always include ray traces at multiple azimuth angles in front of the antenna, unless the reflection zone has uniform terrain, such as several square miles of prairie or seawater. The classic reference on this topic is: https://nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote139.pdf While the NBS publication primarily addresses horizontally polarized antennas, its general conclusions also apply to topband vertical antennas. More than half of the low angle radiation from a 1/4 wavelength 160 meter vertical is formed in an approximately 500 foot wide zone in the direction of propagation from the transmitting antenna to the intended receiver. The far edge of the Fresnel Zone is several miles away for low angle radiation from a 1/4 wavelength 160 vertical, especially if the vertical is installed on a highly conductive surface such as sea water, salt marsh or wet marshy soil. The far edge of the Fresnel zone is much closer when a 160 meter 1/4 wavelength vertical is installed over poorly conducting dry, chalky or sandy soil. A specific worked example: For a 10 degree elevation angle more than half of the radiation from a 160 meter 1/4 wave vertical is formed in an area approximately 500 feet wide in the desired direction of propagation. The near edge of the reflection zone is approximately 3000 feet in front of the vertical and the far edge is about three miles from the the vertical Its obvious that an extensive radial system has no affect at all of the efficiency of the ground reflection in the Fresnel Zone. Radials affect only the efficiency of the antenna itself. 73 Frank W3LPL ----- Original Message ----- From: "K4SAV" <radi...@charter.net> To: topband@contesting.com Sent: Friday, December 18, 2020 4:48:20 PM Subject: Re: Topband: Low Dipoles On 12/18/2020 10:18 AM, Mike Waters wrote: > A few words of wisdom about 160m antennas from W8JI, ON4UN and others... > > https://web.archive.org/web/20180815141931/http://w0btu.com/160_meters.html After you read W8JI's comments, put these two antennas on EZNEC. It will say the dipole smokes the vertical at all elevation angles. I trust W8JI's information because of his experience and his attention to detail when running tests like this. NEC is not telling you the whole story. Jerry, K4SAV _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector