This has been an eye-opening discussion for me! I have always preached the 'gospel' of vertical-is-usually-best based on W8JI, ON4UN, and *many* other long-time Topbanders. Someday I'll have to revise www.w0btu.com/160_meters.html and include a link to this thread.
I stand corrected. Thank you, gentlemen! :-) 73, Mike www.w0btu.com On Mon, Nov 26, 2018, 12:56 AM Steve Ireland <vk...@arach.net.au> wrote: > Hi Frank (and Rick) > > Somewhere I have a map of the lines of geomagnetic latitude superimposed > on a Mercator projection of the world, but I can’t find it right now. > Unlike the ruler-straight lines of conventional latitude, geomagnetic > latitude lines wander across the world like a collection of snake tracks. > > As a result of how geomagnetic latitude snakes across the globe, a > comparison can’t be directly made between similar geomagnetic latitudes in > the northern and southern hemispheres – where Tom W8JI lives is probably > very different to me in terms of the closeness of his geomagnetic latitude > to the electron gyro-frequency. As Carl K9LA points out, the geomagnetic > latitude relates to polarization and involves the ordinary and > extraordinary waves that propagate through the ionosphere, and how 160m is > affected by being close to the electron gyro-frequency. > > About 10 to 15 years ago, Carl, Nick Hall-Patch VE7DXR and Bob NM7M (SK) > (also a physicist like Carl, as I’m sure you recall) helped Mike VK6HD (SK) > and I to understand why our horizontal cloud-warmers outperformed efficient > vertical antenna systems in SW WA. > > You are quite correct, the Fresnel zone where I live (the mostly far field > region where ground gain is developed) has very poor conductivity. And, to > repeat your point as this is not as widely known as it should be, poor > Fresnel Zone conductivity has very little impact on the performance of > horizontally polarized antennas, while having a major impact on vertically > polarised ones. > > While the Fresnel (far field) zone of my location, is basically rock > (granite and ‘coffee rock’), Mike’s final location beside the Kalgan > estuary appeared to have much better Fresnel zone conductivity, with less > rock than me and, in around half the compass directions, salt water. > However, his inverted-L with an 80’ vertical section over 120 buried > quarter-wave radials at Kalgan performed only marginally better than our > previous attempts at vertical antenna systems did. > > On this basis, I came to the conclusion that the dominant problem was > likely to be the geomagnetic latitude issue, rather than poor conductivity > in the Fresnel zone – which it certainly is also an issue here. > > To investigate this further, I sought out the opportunity to operate > directly by the sea here with a good vertical antenna. After much > paperwork, I managed to get permission to operation from the Cape Leeuwin > lighthouse, which is 40m-plus high and on a narrow finger of land > surrounded by sea for over 300 degrees. > > In a Stew Perry TBDC in the early 2000s, with the assistance of my friend > Phil VK6PH, we put up a full-sized quarter-wave wire vertical on the most > seaward side of the lighthouse, less than 60 metres from the sea. This was > fed against a quarter wave counterpoise and the feeder decoupled with a > large ferrite choke to stop common mode effects. On the other side of the > lighthouse was an inverted vee half-wave dipole. Both antennas were > supported from the lighthouse balcony (at about 40m!) and detuned when not > in use. An Yaesu FT-1000MP was used, running less than 100W > > Unfortunately conditions were poor during our evening time into North > America, but at about three hours before sunrise the 160m band opened into > Europe. Right from this point, the vertical was slightly down on the > inverted vee by a few dB, but I would always call on the vertical first and > then switch onto the inverted vee if I got no response. All the way until > just after sunrise, the inverted vee outperformed the vertical, mostly > raising the stations who did not hear us on the vertical. > > The only time this situation was reversed was when 160m started to go out > as the sun started to rise and I had by then switched over to just calling > stations on the inverted vee. > > After about five minutes of this, the Europeans I could still hear were > not coming back to me anymore. Out of curiosity, I switched to the > vertical – and found I could still raise a few of them. I recall vividly > the last QSO with a CT1 using the vertical about 20 minutes after sunrise, > exchanging 559 reports. > > The crazy thing is that the vertical appeared to be doing exactly what a > dipole is known for doing on 160m in the northern hemisphere in some cases > – extending the sunrise opening. However, this was the only time the > vertical outperformed the inverted vee. > > As far as I know, Mike VK6HD never experienced this phenomenon when he was > comparing his inverted-L quarter wave antenna against his inverted vee > dipole. However, my vertical antenna was directly adjacent to the sea, > surrounded by sea, which may have helped. > > The final event was highly interesting, but did not sway me into repeating > the experiment the following year when I also operated from the lighthouse > in the Stew Perry TBDC. > > The fact was the inverted vee had been responsible for 80 to 90 per cent > of my QSOs - can’t remember exactly how many – while the vertical had only > accounted for three or four. > > Mike VK6HD, Phil VK6GX and I are not the only ones to have experienced the > “verticals aren’t always best for DX” situation here. About five to ten > years ago, I understand a group of German DXers came here and operated in > the CQ WW CW (I think). > > The group operated from the the Northern Corridor superstation > VK6ANC/VK6NC, using a quarter wave vertical on 160m. After disappointing > results, one of the ops (Mar DL3DXX, I think) recalled Mike, Phil and I > used inverted vees at 90 to 110’ and suspended a inverted vee dipole as > high as they could and changed over to using this. My understanding is then > they found they could work a much larger amount of DX stations on 160m. > ... _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector