Being a recent newbie to the LEOs it had never even occurred to me that too narrow a beam width could present a problem with staying pointed at those satellites. Thanks, Reid, for bringing that thought up in my mind. I wasn't taking it out of context. I was just wondering if it was an unforeseen problem (by me) that I needed to address. It's things like this that allow us to learn.
It appears that a narrow beam width is not normally a problem and I thank John and others who pointed that out.
73, Tom, KØTW
I have used a Cushcraft 13B2 (13 elements) on 2m and a Cushcraft 719B (19
elements) on 70cm on the
satellites with no problem. Didn't experience either as being too narrow
beamwidth for sat use.
73s John AA5JG
I am amazed at how many people take things stated out of context on this reflector. I never said that any of the arrays would not work due to problem they were having hearing the satellites and it was stated that if none of the other suggestions worked to consider that the arrays they are using are pointed correctly in the correct direction of the satellite. Pointing being off, the nulls could easily block the satellite's reception. The larger the array the more this might be evident. The larger the array, stacked arrays and even dish antennas, pointing becomes a bit more critical.
Reid, W4UPD
On Mon, Nov 30, 2009 at 6:35 PM, Tom [email protected] wrote:
Being a recent newbie to the LEOs it had never even occurred to me that too narrow a beam width could present a problem with staying pointed at those satellites. Thanks, Reid, for bringing that thought up in my mind. I wasn't taking it out of context. I was just wondering if it was an unforeseen problem (by me) that I needed to address. It's things like this that allow us to learn.
It appears that a narrow beam width is not normally a problem and I thank John and others who pointed that out.
I'm going to elaborate on this discussion, for the benefit of beginners who are considering building new stations with tracking antennas. The narrower the beam, of course, the greater the gain when pointing at the bird, both transmit and receive, and -- this is the critical issue -- the lower the gain when you are pointed away from the bird. Now with LEO satellites, some of which cross the sky in say 15 minutes, you need to have everything spot-on if your beamwidth is very narrow: the station clock has to be accurate within a second, the keps have to be up-to-date, etc. otherwise, your computer is telling the rotors to point in the sky where the satellite is going to be in five seconds, or will be in five. Especially with high passes, you can be off by enough to not be able to hear the bird at all. So on receive, long antennas, besides the additional expense and challenge of mounting them, also add the challenge of getting your station perfectly aligned, or you'll hear zippo.
On transmit, long antennas present another challenge: they 'concentrate' your signal so that it might well be excessively powerful for the satellite in question. If my homebrew 7 - element 70cm yagi often needs to be down around 5w xmit on VO-52 to be in the right range of effective power, how will I deal with things when I have a 40-element beam? By all rights, I should put an attenuator between the rig and the antenna so that I can get down under a watt! It is my opinion, in fact, that a significant proportion of the over-powered signals on our birds are from people in just this situation: people using HEO antenna systems that simply can't provide a small enough signal!
In fact, LEO satellites do not require these sorts of antenna systems for reliable use. A beginner will be perfectly happy with, say, four elements on 2m and 6-7 on 70cm (assuming the use of low-noise preamps, which you are *crazy*to do without on long antennas, too). The beauty of this system is that if a high wind knocks it slightly out of whack in azimuth, it will not be the end of your satellite work: you'll just have weaker signals, not silence. The other beauty of this system is that it doesn't require an elevation rotor *at all*. Because the elevation pattern of the antennas will more-or-less fill the sky if you point the array up about 10-20 degrees (make it 10 if you have a clear horizon). Now, suddenly, you've avoided all the hassle of another rotor, you've made your array lighter and easier to work with, and you have way less of a demand on your pointing system. Heck, if you want to go ol' school, you can do the pointing yourself with a twist of the dial.
These yagis do not need to be brilliantly built: mine were made with welding rod and pine wood. They had very strange lobes off the side, and all the rest, but they netted me lots of Q's and were very reliable.
To be even more radical, I urge beginners to start with omni-directional antennas and low-noise preamps. A wire dipole or a vertical, both with almost no coax between them and the preamp, should hear 'stuff' really well. Not Q-5, but a start. Then use this as a baseline from which to compare the theoretical and real-world improvement you get with your yagi array. If you aren't getting improvement, then work out what's up.
This is not an argument against long arrays. I'm building some that I bought from someone on this list around this time last year. I want to do some exotic stuff like work Russia over the pole on AO-07 or hear every last beep out of the newest cubesat. But I'm aware that in my windy region these are going to be a bear to keep in place. So I'm putting as much work into an omni array, too. I plan to transmit from the latter when things get too QRO.
I guess in summary I'd say that in my opinion a big antenna array isn't like a high-power computer, which works the same as a lower-powered one, but has the umph when you need it; it is like buying a high-powered plane as a new pilot: significantly more challenging, and possibly leading to frustration.
73, Bruce VE9QRP
I have used a Cushcraft 13B2 (13 elements) on 2m and a Cushcraft 719B (19
elements) on 70cm on the
satellites with no problem. Didn't experience either as being too narrow
beamwidth for sat use.
73s John AA5JG
I am amazed at how many people take things stated out of context on this reflector. I never said that any of the arrays would not work due to problem they were having hearing the satellites and it was stated that if none of the other suggestions worked to consider that the arrays they are using are pointed correctly in the correct direction of the satellite. Pointing being off, the nulls could easily block the satellite's reception. The larger the array the more this might be evident. The larger the array, stacked arrays and even dish antennas, pointing becomes a bit more critical.
Reid, W4UPD
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
All excellent points Bruce and I might add to any beginners out there, the reason I went the way I did with my antennas back when I had my full blown satellite rig is that I "wanted" the challenge of building a homebrew AZ/EL setup. I did enough research to know that it certainly wasn't necessary for LEO's, omni's are fine. I'm considering homebrewing some eggbeaters, groundplanes and turnstiles just to experiment with. I guess I got it from my late father ( the original W4HIJ), I like to play with antennas. :-) Michael Bruce Robertson wrote
I'm going to elaborate on this discussion, for the benefit of beginners who are considering building new stations with tracking antennas. The narrower the beam, of course, the greater the gain when pointing at the bird, both transmit and receive, and -- this is the critical issue -- the lower the gain when you are pointed away from the bird. Now with LEO satellites, some of which cross the sky in say 15 minutes, you need to have everything spot-on if your beamwidth is very narrow: the station clock has to be accurate within a second, the keps have to be up-to-date, etc. otherwise, your computer is telling the rotors to point in the sky where the satellite is going to be in five seconds, or will be in five. Especially with high passes, you can be off by enough to not be able to hear the bird at all. So on receive, long antennas, besides the additional expense and challenge of mounting them, also add the challenge of getting your station perfectly aligned, or you'll hear zippo.
On transmit, long antennas present another challenge: they 'concentrate' your signal so that it might well be excessively powerful for the satellite in question. If my homebrew 7 - element 70cm yagi often needs to be down around 5w xmit on VO-52 to be in the right range of effective power, how will I deal with things when I have a 40-element beam? By all rights, I should put an attenuator between the rig and the antenna so that I can get down under a watt! It is my opinion, in fact, that a significant proportion of the over-powered signals on our birds are from people in just this situation: people using HEO antenna systems that simply can't provide a small enough signal!
In fact, LEO satellites do not require these sorts of antenna systems for reliable use. A beginner will be perfectly happy with, say, four elements on 2m and 6-7 on 70cm (assuming the use of low-noise preamps, which you are *crazy*to do without on long antennas, too). The beauty of this system is that if a high wind knocks it slightly out of whack in azimuth, it will not be the end of your satellite work: you'll just have weaker signals, not silence. The other beauty of this system is that it doesn't require an elevation rotor *at all*. Because the elevation pattern of the antennas will more-or-less fill the sky if you point the array up about 10-20 degrees (make it 10 if you have a clear horizon). Now, suddenly, you've avoided all the hassle of another rotor, you've made your array lighter and easier to work with, and you have way less of a demand on your pointing system. Heck, if you want to go ol' school, you can do the pointing yourself with a twist of the dial.
These yagis do not need to be brilliantly built: mine were made with welding rod and pine wood. They had very strange lobes off the side, and all the rest, but they netted me lots of Q's and were very reliable.
To be even more radical, I urge beginners to start with omni-directional antennas and low-noise preamps. A wire dipole or a vertical, both with almost no coax between them and the preamp, should hear 'stuff' really well. Not Q-5, but a start. Then use this as a baseline from which to compare the theoretical and real-world improvement you get with your yagi array. If you aren't getting improvement, then work out what's up.
This is not an argument against long arrays. I'm building some that I bought from someone on this list around this time last year. I want to do some exotic stuff like work Russia over the pole on AO-07 or hear every last beep out of the newest cubesat. But I'm aware that in my windy region these are going to be a bear to keep in place. So I'm putting as much work into an omni array, too. I plan to transmit from the latter when things get too QRO.
I guess in summary I'd say that in my opinion a big antenna array isn't like a high-power computer, which works the same as a lower-powered one, but has the umph when you need it; it is like buying a high-powered plane as a new pilot: significantly more challenging, and possibly leading to frustration.
73, Bruce VE9QRP
participants (3)
-
Bruce Robertson -
Michael Tondee -
Tom