> The NEC surface wave includes low-angle fields well above zero degrees > elevation that do not appear in a NEC far-field plot, and they are in fact > space waves (see link below).
And that's the piece that probably not been underscored in this discussion. Some have probably concluded that the surface wave plot in NEC only includes ground wave conduction. An interesting exercise I went through a couple days ago (using NEC/4.2): distance was varied between 1km and 10km from a 160m 1/4-wave vertical radiator over a 60-radial field. I then modified the ground conductivity between poor and very good while observing the surface wave plot with changing distance. Even over average ground, and unlike the far-field analysis, the surface wave and the space wave are reasonably close out to about 4-5 km. That's roughly 25-30 wavelengths on 160m. Over poor earth, you start seeing the effects low-angle field strength attenuation much earlier as is expected. So, just how much distance is required to effectively launch a 160m field into the ionosphere to the point where the ground surface and conductivity is no longer relevant? By 25 wavelengths, can we safely say that "it's launched" absent some other factor like a mountain range? How about 5-10 wavelengths -- is that enough? Clearly, the traditional far-field plots are at odds with the NEC surface wave plots (that also include the space wave as Richard mentions) in that unless the ground is extremely poor, the far field plots are not accurate as far as NEC is concerned. Yes, the far field plot does show the lobe from a ground-mounted vertical radiator coming down closer and closer to the earth as ground conduction improves but only gets there with super-conductive ground like salt water, leaving us to conclude that with normal earth conductivity there's no field at all below the far-field curve. A surface wave plot over salt water does show extremely close field strength over very long distances between the far field and surface wave as one might expect. So, if the NEC surface wave tool is accurate, we've not been looking at the entire picture when considering only far-field analysis. Paul, W9AC _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
