| Index | Thread | Archive | Apr-2003 | Archive | Send |
 |
  |
|
   |
|
  |
|
very same thing that I seem to be experiencing. I just measured the hillside - its a 23 degree incline directly east of the antenna, and for hundreds of yards. And when I work the longpath to the Southwest, I seem to be able to work anything that I can hear - and I break huge pileups about 90 percent of the time. Africa and the Middle East are difficult from the West Coast going NE, but I have no problems going SW. In fact, I usually will use my 30M horizontal dipole up 35' (oriented NE - SW) when there isn't too much high angle noise for short(er) path DX. Using that dipole on 20M and above I get a pretty nice pattern and TO angle - especially on 20M. I did sell my Sigma 40XK to a local good friend - and am trying to do what I want to do with only 2 antennas that are as inconspicuous as possible. I do seem to have what I want / need. (If that is ever possible in ham radio). For short path Oceania and Asia - I consistently can work anything with 5 watts on every band and mode this winter. At 100W I can break huge pileups - like VP6DIA with only a few calls. I worked AH3D, JD1, ZK3SA and T31MY on every band / mode they were on with either 5 or 100W. For the Middle East and anything but South Africa I need the amp - but never go much above 400W. I do follow the "use only what you need to get the job done" rule of thumb. I do believe that not only less is more - but its a better challenge. I don't think I ever stated my goal - which is to get to DXCC Honor Roll during this cycle. I have 266 entities and pretty much only need entities that are on the long or short path in the NE - SW direction. After this I will just settle on using my Argonaut V to work DXCC using only 5 watts - and these same 2 antennas. Thanks again - what a great thread! Rich KY6R ----- Original Message ----- From: "Alan Day" <k8al@juno.com> To: <rholoch@attbi.com> Cc: <Force12Talk@qth.com> Sent: Friday, April 25, 2003 09:05 Subject: Re: [Force 12 Talk] Sigma 5 Height > Hello, Rich... > > It appears that your questions regarding optimal mounting height for your > Sigma 5 have been very well addressed by the reflector members. I just > want to reply to the question in your initial message about the effect of > a hillside on an antenna's radiation pattern. The answer is a resounding > "Yes!" - it can make a huge difference. > > Theoretically, if your antenna were mounted on a continuous downward > slope of, say, ten degrees, and the slope extended throughout the fresnel > zone for a given frequency, you would simply subtract ten degrees from > the takeoff angle you'd have over flat terrain. In practice this is > seldom the case, as sloping terrain is usually irregular, and the takeoff > angles are formed by a complex interaction of reflection and diffraction. > About the only way to look at this is by computer simulation, and I like > Brian Beezley's (K6STI) old DOS-based TA program. From my own > experience, the plots shouldn't be taken too literally, but they seem to > give an excellent approximation. Note that it plots only for a > horizontally polarized wave, but I've found that the actual performance > of verticals seems to be similar. > > For quite some time now, I have had a second QTH in an old trailer on a > steep hilltop rising about 350' over average terrain (photo on QRZ.com). > I don't get to use it as much as I'd like, but it definitely works; when > I first started using it, it almost literally seemed magical. With 300 > watts and a modest 20m yagi at 63', I was easily working low-power > central Asian stations that almost no one else could even hear. Years > later, when the TA software came out, I saw quantitatively what was > happening. On the plots, sharp low-angle lobes in many directions were > as much as 20 db over the same-angle lobe formed on flat terrain. > > For long-haul dx, this very modest hilltop station usually holds its own > even against the really incredible superstations that have appeared in > recent years. However, it does not have the versatility/adaptability of > stations with multiple switched stacked yagis on 200' towers, and will > often lose out when propagation favors the higher angles. And, of > course, the brute force of four stacked six-element yagis over flat > terrain, fed with a 3 kw amplifier, is simply very effective. But I get > a lot more decibels per dollar! > > 73, Al K8AL > -------------------------------------------- Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. Force12 Web Site: http://www.force12inc.com To Submit Message to the List: Force12Talk@qth.com To unsubscribe and view the Message Archive: see http://qth.com/force12/list For problems with the list: contact n4zr@qth.com |