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lining up microwave antenna's
Maybe somebody can shed some light on the following matter:
Recently I have installed an 18 GHz Microwave link, consisting of NEC- Pasolink gear and Andrews Microwave Dishes. Because it was a first for me, I had thought over the process of lining up the dishes. I had heard of and read about the side-lobe vs the main- lobe. So I figured out the my coworker on the other end of the link should move his dish and I would tell him the reading on my voltmeter. The higher the better and at the peak reading he would fix the dish. Then I would do the same on my end. And then his end a second time and then my end a second time We would repeat this procedure for the vertical line-up as well. I had calculated an expected attenuation which could be converted in a voltage reading. Assume the reading should say 3,5 V. Well I never got anything better than 2.8 / 2.9 volt. COnsequently I asked NEC for advice and they said that 'you should line up you own end using the voltmeter, and not the opposite end'. With this advice we repeated everything and reached the expected reading of 3.5 volt. The 2.8 volt was a sidelobe of the antenna-beam What I don't understand is that when I rotate my dish (either horizontally or vertically) I can go from sidelobe to mainlobe to sidelobe. I don't move the dish further left or right, I only rotate it around a vertical or horizontal axis. When I would move the dish further left or right or up or down, than I can visualize going from lobe to lobe. Not by rotating the dish That is why I used the opposite end to move the beam. Anybody can explain where I go wrong Regards, Ad |
On Fri, 11 Jul 2003 21:35:16 +0200, wrote:
Anybody can explain where I go wrong Regards, Ad Hi Ad, Looks like cross-polarization issue. As you rotate, they come into conflict (the polarizations) and then re-emerge from conflict. Actually, it sounds fairly bullet proof with what you got (plenty of signal, the system probably doesn't need more than a volt, as you would measure it). 73's Richard Clark, KB7QHC |
On Fri, 11 Jul 2003 21:35:16 +0200, wrote:
Maybe somebody can shed some light on the following matter: Recently I have installed an 18 GHz Microwave link, consisting of NEC- Pasolink gear and Andrews Microwave Dishes. Because it was a first for me, I had thought over the process of lining up the dishes. I had heard of and read about the side-lobe vs the main- lobe. So I figured out the my coworker on the other end of the link should move his dish and I would tell him the reading on my voltmeter. The higher the better and at the peak reading he would fix the dish. Then I would do the same on my end. And then his end a second time and then my end a second time We would repeat this procedure for the vertical line-up as well. I had calculated an expected attenuation which could be converted in a voltage reading. Assume the reading should say 3,5 V. Well I never got anything better than 2.8 / 2.9 volt. COnsequently I asked NEC for advice and they said that 'you should line up you own end using the voltmeter, and not the opposite end'. With this advice we repeated everything and reached the expected reading of 3.5 volt. The 2.8 volt was a sidelobe of the antenna-beam What I don't understand is that when I rotate my dish (either horizontally or vertically) I can go from sidelobe to mainlobe to sidelobe. I don't move the dish further left or right, I only rotate it around a vertical or horizontal axis. When I would move the dish further left or right or up or down, than I can visualize going from lobe to lobe. Not by rotating the dish That is why I used the opposite end to move the beam. Anybody can explain where I go wrong Regards, Ad When aligning the antennas you must swing each all the way left and all the way right to where you are well past the beam width and any lobes. Of course you note the signal strength as you do this. That is the only way to be sure that you are not on a side lobe. Just moving it a little each side of a peak or even moving it until you loose the signal is not sufficient. You could hit a null between the main and a side lobe and think that you have gone far enough but you still could peak on a side lobe. By swinging way past the lobes, each way, and noting the signal strength as you go will assure that you find the main lobe. Do the same in the vertical plane also. 73 Gary K4FMX |
Gary, K4FMK wrote:
"Do the same in the vertical plane also." Never had a minor lobe identification problem. Never improved over the bubble-level set of vertical elevation angle on long paths either, but I always tried. I had always calculated my path gains and losses, and my best received carrier power was very nearly always within a db of my calculations. If not, I had a problem. Fortunately, that was very rare. Best regards, Richard Harrison, KB5WZI |
Floyd Davidson wrote:
"Did you actually do very many?" I`ve done single-hops, several-hop systems, and transcontinental systems. I`ve done them on-shore, off-shore, and in a multi-hop loop system on-shore and off-shore. I`ve done several systems with paths sandwiched between tall buildings. I`ve done 960 radio, 2-GHz, and 6-GHz systems. I`ve done space-diversity systems, hot-standby, and unprotected systems. I`ve done solid-state systems, vacuum-tube systems, etc., etc. I have no reason to say anything which is untrue. Floyd knows of an anomalous hop in the desert. The path suffers reflections, else it would not have great variation of signal with height. I know of many anomalous systems, but I never built one. All of mine worked as designed. Best regards, Richard Harrison, KB5WZI |
(Richard Harrison) wrote:
Floyd Davidson wrote: "Did you actually do very many?" I`ve done single-hops, several-hop systems, and transcontinental systems. I`ve done them on-shore, off-shore, and in a multi-hop loop system on-shore and off-shore. I`ve done several systems with paths sandwiched between tall buildings. I`ve done 960 radio, 2-GHz, and 6-GHz systems. I`ve done space-diversity systems, hot-standby, and unprotected systems. I`ve done solid-state systems, vacuum-tube systems, etc., etc. I have no reason to say anything which is untrue. Floyd knows of an anomalous hop in the desert. The path suffers reflections, else it would not have great variation of signal with height. I know of many anomalous systems, but I never built one. All of mine worked as designed. As I pointed out, that was the most _interesting_ example that I know of. However, you've just stated something that I can't quite get my arms around. "All of mine worked as designed." is stated as if the "anomalous systems" that have a path which "suffers reflections" are somehow not common, or not well designed, or not normal. Yet you mentioned "on shore" and "off shore" each twice above, and I'm having a real difficult time thinking you've ever designed a microwave shot across tidal waters without having "reflections" which could not specifically be calculated. And there is simply no way that it "worked as designed" unless you mean you just allowed for a large enough fudge factor to account for signal swings from day to day. The original claim that they *all* came in within 1 dB is just hilarious. My bet is that you have hung around and do know how these paths function over time, and I'll bet you just exaggerated a little, that's all. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
Floyd Davidson wrote:
"---I`ll bet you just exagerated a little, that`s all." Too many hours of daylight on Floyd are taking their toll. Everything you work with is known. precisely, including path attenuation under normal propagation conditions. Normally, you don`t have a path grazing at a highly reflective point. Your path survey discloses path detractions and you adjust for the possibility of distructive interference. You may opt for a high / low antenna placement for the path ends, diversity, more clearance, shorter paths, and brute-force fade margins. The high / low option lets you move the reflection point and the reflection. Long microwave systems must have huge fade margins anyway due to noise buildup from individual path contributions. A receiver not too much below the overload signal point is a very quiet receiver and contributes almost no noise to a system. When the path design is right, the as-built numbers are almost exactly as calculated, whether you believe it or not. Best regards, Richard Harrison, KB5WZI |
(Richard Harrison) wrote:
Floyd Davidson wrote: "---I`ll bet you just exagerated a little, that`s all." Too many hours of daylight on Floyd are taking their toll. Look like you need some daylight. Everything you work with is known. precisely, including path attenuation under normal propagation conditions. Normally, you don`t have a path grazing at a highly reflective point. Your path survey discloses path detractions and you adjust for the possibility of distructive interference. You may opt for a high / low antenna placement for the path ends, diversity, more clearance, shorter paths, and brute-force fade margins. The high / low option lets you move the reflection point and the reflection. Long microwave systems must have huge fade margins anyway due to noise buildup from individual path contributions. A receiver not too much below the overload signal point is a very quiet receiver and contributes almost no noise to a system. When the path design is right, the as-built numbers are almost exactly as calculated, whether you believe it or not. Lets see, now you are saying that you go out and *measure* the path, rather than calculate it. And of course you measure it, *every* *single* *time*, on a day when you *know* whether it is giving you the best path, the worst path, or some specific point in between. Richard you can cut the bull**** out. I've been measuring microwave paths for 40 years. You don't calculate them to within 1 dB. You might find out what that is after measuring it on a regular basis for a year. (I've done *continous* path measurements of several paths for over a year, and on two for 10 years.) -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
Floyd Davidson wrote:
"Richard you can cut the bull**** out." Floyd claims to have measured microwave paths for 40 years. I`ve been doing it since 1960, so that`s about as long. I`ve made repeated measurements over a number of years on the same repeaters. During normal propagation, which is by far most of the time, path loss like other system losses is very constant. Of course there are periods of anomalous propagation. It depends on location, season, and time of day. It`s worse when the atmosphere is stagnant. I`m sure that marginal paths with insufficient clearance and other problems may have propagation which comes and goes. I`ve seen some, but I haven`t built any like that. Best regards, Richard Harrison, KB5WZI |
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