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A 150 foot boom ( say 20
elements for example) beam might be perfect for picking up t he lower angle, which is what I thought you were looking for. The t hree element beam will bring in higher angle signals as the lobe will have a higher angle. A dipole will likely have even a higher, po ssibly a NVIS angle. ................................... Dunno...I've never compared super long yagi's vs short ones, but I don't think boom length has a drastic effect on the takeoff angle...The height above ground is what really determines that...Same for a dipole...A dipole has a very low takeoff angle *if* it's high enough..The various yagi's takeoff angles *should* be about the same as a dipole at that same height...Or seems to me, without looking into it farther. MK |
On Fri, 28 Jan 2005 23:25:19 -0800, Roy Lewallen
wrote: *Sigh* I tried. You can lead a horse to water..... Roy Lewallen, W7EL Buck wrote: On Fri, 28 Jan 2005 21:28:20 -0800, Roy Lewallen wrote: What does the takeoff angle have to do with which antenna is best? That would depend on the desired contact. If you want 80 meters DX, you want a very high antenna, if you just want to talk to your local buddies, a lower antenna provides a better NVIS. Verticals provide better omni-directional pattern but a slanted dipole provides better directivity than a vertical. Beams are obvious. |
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wrote in message oups.com... A 150 foot boom ( say 20 elements for example) beam might be perfect for picking up t he lower angle, which is what I thought you were looking for. The t hree element beam will bring in higher angle signals as the lobe will have a higher angle. A dipole will likely have even a higher, po ssibly a NVIS angle. ................................... Dunno...I've never compared super long yagi's vs short ones, but I don't think boom length has a drastic effect on the takeoff angle... Mark I never used the word "drastic" however the long boom antenna will lower the TOA by around a degree. The reader has to determine the value of this for himself. If one reviews the incomming signals in the ARRL literature one can see the percentage of signals that come in from Europe at 9 thru 13 degrees.These angles by the way are not to be confused with TOA and explains exactly why a silly db can mean a lot. It also shows that the long boom aproach has its limits with respect to lower TOA and height certainly changes the TOA more in terms of less complexity. What I am looking for is the latter method but with less emphasis on feed point height which will require a deflection method to achieve lower angles. I am sure that multiple reflectors and a single director can be manipulated to do this Regards Art The height above ground is what really determines that...Same for a dipole...A dipole has a very low takeoff angle *if* it's high enough..The various yagi's takeoff angles *should* be about the same as a dipole at that same height...Or seems to me, without looking into it farther. MK |
On Sun, 30 Jan 2005 05:29:13 GMT, "
wrote: Just think of what I could be describing, a 20 metre antenna with a ten to eleven degree TOA, turning radius of a conventional dipole and a feed point of something less than 75 foot high. Now thats good for small real estate and a light duty rotor tho the U.K. authority may baulk at the height. I have built very long boom yagi.s. for 20 M some with a couple of reflectors and some with as many as 13 elements but this direction is limited by minimal advances compared to complexity, thus my statement as to what the hobby needs for it to grow I see what you are asking for. I would definitely want one myself, but the problem I see with your theory is that the antenna can't change the earth's effect on electromagnetic waves. I have never had a beam up 75 feet. I had a TA-33 JR up 35 feet, about half of the height you recommend. I can't say I had the perfect TAO, but compared to the dipole and a vertical I was using before I got it, the beam significantly improved my operating. I was county hunting at the time (operating with mobiles in each US county) and the short beam made the difference between not hearing a car and exchanging 5-9 signal reports. While it wasn't perfect or optimum, it was an improvement. I guess that is the best we can hope for. A better antenna for the same space. I like building mostly wire antennas and I have a few designs in mind and in the works. There are many to choose from to try. Maybe one of them will be an improvement. When it comes to making a contact, I have resigned myself to this one fact: If there is no propagation between two points, there is no communications. If there is enough propagation, even the poorest of stations can communicate. I wish you the best on your DXing and antennas. I've enjoyed the topic. 73 for now. Buck N4PGW -- Buck N4PGW |
On Sat, 29 Jan 2005 21:56:36 -0800, Roy Lewallen
wrote: Buck wrote: . . . If I hang the vertical here, the top will be about 65 feet above ground. The dipole feedline will be about 15 feet away and the center of the dipole about 50-55 feet high. I doubt they will interact with each other. The dipole feedline and the vertical will interact a great deal unless you take steps to prevent it. That would be to insert one or more "current baluns" (otherwise known as choke baluns and common mode chokes) in the dipole feedline. Roy Lewallen, W7EL Would the 'ugly balun' be suitable? (wrap 8-10 turns of coax in an 8 inch diameter loop) That is the standard 1:1 balun I use. Thanks. I did see a difference with my two 20 meter dipoles. I had one stretched, say, due north (0 deg) about 55 feet and another about 45 feet stretched about 75 degrees off. The shield side of both antennas is where they crossed. I noticed that when I lowered one antenna the signals seemed stronger from other directions. It didn't make either unusable though and after Francis hit Florida, I took down the lower 20 to take with me in case I needed it and never put it back up. -- Buck N4PGW |
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On Sat, 29 Jan 2005 07:54:16 -0600, Cecil Moore
wrote: Maybe a picture is worth a thousand words. Here's a comparison radiation pattern for my 130 ft dipole Vs my 40m vertical with elevated radials. In the dipole's favored direction, it's TOA is greater than the vertical's yet the dipole radiates more power than the vertical even at the vertical's TOA. Here's the pictu http://www.qsl.net/w5dxp/dipvsver.htm Exactly! |
Buck wrote:
I am thinking that I might be able to improve my contacts by using a vertical antenna since most mobiles use vertical antennas. I have heard that once the signal bounces off the ionosphere, polarity isn't as important as it is for local communications. However, when I was assembling a 2 meter dipole antenna, I held it horizontal and turned it vertical. I saw the s-meter go from nothing to s-7 and the repeater go from silent to full quieting when I did this. I can't help but wonder how much difference it will make with the mobiles. 2m signals don't bounce off the ionosphere. It is not clear what band you are talking about. For sky wave communications on HF, the polarization doesn't much matter. For ground wave communications, polarization matters. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
On Sun, 30 Jan 2005 12:56:05 -0600, Cecil Moore
wrote: 2m signals don't bounce off the ionosphere. It is not clear what band you are talking about. For sky wave communications on HF, the polarization doesn't much matter. For ground wave communications, polarization matters. -- 73, Cecil http://www.qsl.net/w5dxp Primarily 20 meters, maybe 40 meters. Thanks -- Buck N4PGW |
Roy, W7EL wrote:
"So you`ve improved your transmit effectiveness but haven`t improved your ability to receive." Exactly, for Roy`s mpre radials under a vertical antenna. For horizontal antennas, it`s another matter. The horizontal discriminates against vertically polarized signals. Both polarizations result from ionospheric reflection of a signal of either polarization. The most annoying noise usually originates locally and travels to the receibver by a vertically polarized wave, the only polarization propagated by a ground wave. A horizontal antenna is insensitive to vertically polarized waves, so improving its efficiency possibly improves reception of horizontally polarized waves without a corresponding increase in noise reception. I worked for years in a system which relayed its broadcast programs by HF radio. This was before satellites, jets, and great recording quality. We also needed immediate relay capability for breaking news. All HF relay systems were horizontally polarized. Best regards, Richard Harrison, KB5WZI |
Thing is....So did my model when using "medium" ground quality.
But I know in the real world, my vertical smoked the dipole on long haul/low angles. I'm almost positive that the verticals are "underpowered" when modeling, unless you bump up the ground quality. Or at least when used on the low bands at night. To make the model of my dipole vs vertical actually pan out as in real life, I had to bump up the ground quality to "excellent". Even then, it might have been a bit lower than real life. I'm not sure what to make if this.... I'm not the only one to notice this also.... Talk to W8JI about his nearly 300 ft dipole vs his verticals on 160m...He always thought the dipole would be better. After all, modeling says it should be. But it didn't quite pan out... I basically ignore Cecils bad experience, because #1, his vertical needed more radials, and he never used it for long haul paths. So of course, the vertical should have lost in his case. Heck, even with my vertical, that was a bit better than his, I had to get over 1000 miles to start seeing the vertical overtake the dipole. Those dipole vs vertical modeling plots are *very* misleading. Or to me anyway... Myself, I think the ground qualities applied are in error for some reason.. They overly stunt the vertical when modeling...Either that, or my ground here is really good...My ground quality is pretty good, but it's not *great*, being I'm in the city cement jungle of Houston. MK |
On Sun, 30 Jan 2005 12:56:05 -0600, Cecil Moore
wrote: Buck wrote: I am thinking that I might be able to improve my contacts by using a vertical antenna since most mobiles use vertical antennas. I have heard that once the signal bounces off the ionosphere, polarity isn't as important as it is for local communications. However, when I was assembling a 2 meter dipole antenna, I held it horizontal and turned it vertical. I saw the s-meter go from nothing to s-7 and the repeater go from silent to full quieting when I did this. I can't help but wonder how much difference it will make with the mobiles. 2m signals don't bounce off the ionosphere. It is not clear what band you are talking about. For sky wave communications on HF, the polarization doesn't much matter. For ground wave communications, polarization matters. A couple of years ago I was keeping a sked with a friend on 10 meters. The path was about 1800 miles. I mounted a vertical element on the end of the 3 element beams boom. I wanted to try circular polarization. By using proper feed line lengths and switches I could switch between right or left hand circular polarization. The beam had a little more gain than the single vertical element but the effects were dramatic at times. Sometimes right hand was best sometimes left hand was best. But what turned out to be interesting was when both vertical and horizontal where in phase and connected together. It lowered overall signal strength a little but the fading was much less. At times signals would fade deeply on either vertical or horizontal polarization. Circular helped a lot but the signal kept changing between left hand and right hand so you had to keep flipping the switch. With both antennas in phase it would receive vertical or horizontal without changing anything. Very smooth constant signal. At other times just the beam was better alone. Transmit appeared to benefit the same. He could hear me with less fading with the in phase antennas as well. My friend on the other end only had horizontal polarization. He was going to try a vertical element too but never got to do it before 10 meters died. 73 Gary k4FMX |
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All HF relay systems were horizontally polarized.....
I wonder about the time of day and freq? I'd almost bet many were in the daytime, and using fairly high frequencies as far as HF. IE: 31,25,19 m, etc... Seems the choice was as much a receiving/noise consideration rather than absolute signal strength. I think the choice is much more complex than any theoretical gains seen in modeling, ect. In the daytime, I don't think it really matters much. So in that case, it would probably make sense to use horizontal to reduce local noise pickup. That would improve the receive s/n. As far as transmit strength, probably not a whole lot of difference either way. But at night, it seems to be a different ballgame. I think the differences in propagation skew things towards the vertical on the low bands at night. The farther the path, the better the advantage. It could be stated that most horizontal wire antennas are lower to the ground in terms of wavelength on those bands. This is true. But you still have cases where people have tried the high antennas on the low bands, and still see the verticals usually win on long paths. I've never tried it, but any interested could model my 36 ft high dipole, and then model my 10 ft center loaded mobile whip, on a ford truck. I'd almost bet the dipole creams the mobile antenna in the model at low angles as far as the gain numbers shown. But I know in the real world, that mobile beats the 36 ft high dipole from Houston to Jacksonville Fla at 2 AM. Yes, even I was surprised the first time I saw it. But I tried it over, and over again, and it was not a fluke of nature. If you could have two 160/80/40 m antennas at 1 wave up, both with the same exact gain, IE: one a 1/2 wave vertical with any radials needed to equal the ground loss of a horizontal dipole, I'd bet money the vertical would win on long paths 95% of the time. It's not just a pure "gain" thing.... I think even verticals with less gain will win over the dipoles once the path becomes long enough. Note my mobile... I know for a fact from real life, if you are going to run a dipole, and expect to equal my 36 ft high ground plane, you better plant that puppy *WAY* high, or you won't have a chance. I'm talking over a 1/2 wave up. More like a full wave, and even then you might lose, once the path gets to about 4k or so... BTW, these days in Houston, local noise has just as good a chance being horizontal as vertical...Most is powerline noise...So with my vertical, I never really noticed any extra noise. The s/n ratio was always better on the vertical, for long haul. IE: if the noise comes up 1 s unit, but the desired signal 2 s units, the noise is a non factor...Many times I saw no extra noise on the vertical. MK |
Well...Depends on what part of town...On the coast, it's great. A 30...
But in town, they rate it as about a 15. But that would vary greatly I'm sure...I'm in a suburban area, so I might be maybe a "20" ??? I know that I had very mediocre results using ground mounted verticals. I had one with 32 full length radials, and it was poor compared to my ground plane at 36 ft, with 4 radials. It was probably about as good as Cecils vertical he ran....LOL...:/ MK |
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Gary Schafer wrote:
Sometimes right hand was best sometimes left hand was best. Indicating that, for a single antenna, polarization doesn't much matter for HF skip since it is continuously changing. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Mark, NM5K has raised some interesting questions. Time of day and
frequewncy? We operated almost around the clock with both broadcasting and program relay. For broadcast, the schedules are based on propagation predictions and must be published far in advance. The schedule must be followed no matter how propagation actually turns out. The best likely frequency is picked for the path. Also scheduled is something in the next lower frequency band and something in the next higher frequency band. For program relay, you can make unscheduled frequency adjustments at any time it is convenient to do so. Triple space diversity was the method we mostly used. (3) separate receiving antennas, spaced about 10 wavelengths apart laterally at 40-meters (400 meters) were used to receive all relayed programs. Each antenna fed a multicoupler so that receivers could be connected without interaction. The three receivers tuned to a particular program (not necessarily the same frequency) had their outputs fed to a single TDR combiner (Crosby or Pioneer). The combiner accepted the best output of the three receivers and rejected the other two. An operator checked the reception regularly to see if the signal could be improved by selection of either the upper or lower sideband, or other means. The height of the antennas was about 20 meters. High enough for single-hop propagation over the path at midday on the 20-meter band. We had fixed height so it had to serve from 5 MHz to 18 MHz at all hours. For relay, we adjusted frequencies almost 24-hours to pick those frequencies which were working best at the time and might also be transmitting in the next higher and/or lower band during changing conditions For relay we used 3 to 5 KW. For broadcast we used 50 KW and 100 KW. Antennas had about 15 dBd gain on both relay path ends. For broadcast we used 15 dBd gain on the transmitter. The receiver may have had a wet noodle for an antenna. If it was good enough for the jammers it was probably good enough to receive us too. Mark also wrote: "I`d bet money the vertical would win on the long paths 95% of the time." The vertical has its null directly overhead, and it has its maximum radiation at low vertical angles from the horizontal. A hazard for the vertical is low uncorrected soil conductivity benearh the antenna. Put the horizontal antenna up high and it works with either low conductivity or high conductivity soils. Low height is the hazard for the horizontal antenna if you want DX. Best regards, Richard Harrison, KB5WZI |
Hummm. Maybe that explains the large difference I saw between it and
the ground mount. I know the antenna seemed to really come alive once it's up about a 1/4 wave. I never was too crazy about ground mount verticals. To me, it's like ground mounting a dipole...Makes about the same sense....Of course, the GP may not be for everyone...Not really hard to put up, but it's a 68 ft tall antenna, the way I had it installed. I took it down a couple of summers ago, because the lightning had been so bad. Was paranoid I'd take a hit eventually...It was boom-boom every day at that time...It's now resting on the side of the house.. MK |
Put the horizontal antenna up high and it works with either low
conductivity or high conductivity soils. Same for the vertical. Low height is the h azard for the horizontal antenna if you want DX. Yes, but even high, they aren't always the best choice on the low bands. In a way, I think the same can apply to the verticals. Low height is a hazard for those too, unless you have a load of radials...:/ MK |
Dear MK (NM5K):
I do not understand. Why speculate? In the over forty years that I have been involved with the prediction of HF propagation, huge progress has transpired in the ease with which one may investigate the issues that seem to be of interest. Today, one may download and run a series of computer programs that will provide statistically significant answers to your questions. The programs have evolved over decades and are refined. Go to: http://elbert.its.bldrdoc.gov/hf.html As Reg might say: ready to run. Numbers tell the story. Enjoy. 73 Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: |
J. Mc Laughlin wrote: Dear MK (NM5K): I do not understand. Why speculate? In the over forty years that I have been involved with the prediction of HF propagation, huge progress has transpired in the ease with which one may investigate the issues that seem to be of interest. I'm not sure I understand. Why speculate about what? Verticals vs dipoles? Or do you mean propagation only? Or you talking about qround quality per a certain area? Today, one may download and run a series of computer programs that will provide statistically significant answers to your questions. The programs have evolved over decades and are refined. Go to: http://elbert.its.bldrdoc.gov/hf.html As Reg might say: ready to run. Numbers tell the story. Enjoy. Tell what story? I might try downloading them, but what is it I'm trying to find out? What are my questions? I'm not overly keen on downloading a potentially large program, I then have to install, and take up more room, without knowing what it is I want to do with it, or even what it does... You are leaving me in the dark too much as to what this program does...Even they don't give a real description.. MK |
If you'd like something simpler, I highly recommend W6ELProp, a free and
very capable propagation program. (Note that's W6EL, not W7EL.) Shel, W6EL, created the DOS program MiniProp and sold it for many years. When time came for the major job of rewriting the program for Windows, Shel did it -- and generously made the program free, as W6ELProp. It doesn't do the fancy graphics of the big government programs, but its predictions are quite good, and it's very easy to use. I've used it and its predecessor MiniProp for a long time. You can get W6ELProp at http://www.qsl.net/w6elprop/. Roy Lewallen, W7EL wrote: Tell what story? I might try downloading them, but what is it I'm trying to find out? What are my questions? I'm not overly keen on downloading a potentially large program, I then have to install, and take up more room, without knowing what it is I want to do with it, or even what it does... You are leaving me in the dark too much as to what this program does...Even they don't give a real description.. MK |
Dear MK:
You speculated about the performance of some antennas. Performance includes antenna gain distribution and ionospheric propagation. The programs that I, and others, mentioned would provide you with meaningful performance numbers. I thought that you might wish to know the performance of the antennas you discussed over the paths mentioned (and other paths). Such knowledge might reduce the uncertainty of the speculations. It is an engineering sort of thing. Not all are enamored of changes in entropy. Please disregard my suggestion. It was not matched to your desires. Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: wrote in message oups.com... J. Mc Laughlin wrote: Dear MK (NM5K): I do not understand. Why speculate? In the over forty years that I have been involved with the prediction of HF propagation, huge progress has transpired in the ease with which one may investigate the issues that seem to be of interest. I'm not sure I understand. Why speculate about what? Verticals vs dipoles? Or do you mean propagation only? Or you talking about qround quality per a certain area? Today, one may download and run a series of computer programs that will provide statistically significant answers to your questions. The programs have evolved over decades and are refined. Go to: http://elbert.its.bldrdoc.gov/hf.html As Reg might say: ready to run. Numbers tell the story. Enjoy. Tell what story? I might try downloading them, but what is it I'm trying to find out? What are my questions? I'm not overly keen on downloading a potentially large program, I then have to install, and take up more room, without knowing what it is I want to do with it, or even what it does... You are leaving me in the dark too much as to what this program does...Even they don't give a real description.. MK |
J. Mc Laughlin wrote: Dear MK: You speculated about the performance of some antennas. Performance includes antenna gain distribution and ionospheric propagation. The programs that I, and others, mentioned would provide you with meaningful performance numbers. I thought that you might wish to know the performance of the antennas you discussed over the paths mentioned (and other paths). Such knowledge might reduce the uncertainty of the speculations. It is an engineering sort of thing. Not all are enamored of changes in entropy. Please disregard my suggestion. It was not matched to your desires. If you say so...I just wanted to know what the program does.. I don't have a lot of room on my drive, and when they start talking about "install" programs, ect, it makes me think the program is pretty large. I don't think I really "speculated" about the antennas. I just described my results with them. I did speculate as to why I have to bump up the ground qualities in the modeling programs to match my real life results. But I think Richards theory about the elevated performance was about as good as any. I may try some of the programs later. I need to get a new drive..My present one is crammed full..I have to shuffle junk around to make room for big programs. My flight sim, and 1000's of old pictures I store, hog all my room...Not to mention a zillion zip files...I'm like a packrat when it comes to data....:/ Time for a new big drive...I rebuilt my puter last summer, but not the drive yet...I'm still on a puny 6.8 g. I need about a 100 g... BTW...I'm not sure why my type is constantly messed up as far as the lines, etc. I'm using google, and I *hate* their post entry window...It doesn't autowrap like I'm used to, and I never know how to make it look normal...If you try to let it autowrap the lines, it just types off to the right forever...I never had this problem with the old google...If I try to match the width of the previous post, it still usually ends up all goofed up...Don't worry...It's not an excess of wine causing the problem. :/ MK |
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