[amsat-bb] Re: satellite average elevation new birds
... asking Bob to comment on his earlier thoughts on using antennae at fixed elevations? The geometry of LEO satellites has not changed. The optimum angle for a fixed tilt modest gain YAGI is about 15 degrees (assuming you have a decent horizon). See: http://aprs.org/LEO-tracking.html That said, if your antenna is seriously blocked from all directions below say 10 degrees, then you are not going to hear anything down there anyway. So bump it up to say 20 or 25. But 70% of all LEO passes are below 22 degrees so just recognize that you are giving up most of your operations. Bob, Wb4aPR -Original Message- From: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] On Behalf Of Clayton Coleman Sent: Tuesday, December 17, 2013 8:35 PM To: Ted Cc: AMSAT-BB Subject: [amsat-bb] Re: satellite average elevation new birds Just a short time ago after I moved into a new shack, I operated for a month with an Elk at 15 degrees on a tripod. Armstrong rotor. I worked all the current satellites right up through the first week we had AO-73's transponder available. Pay close attention to comments WB4APR has made about setting the fixed elevation based on the lowest horizon you can work. For example, if it takes ten degrees for you to clear a mountain, twenty five degrees is probably okay. If you have a clear horizon view, fifteen is probably okay. The goal is to have as much gain available at your lowest elevation to increase your available range. YMMV PS A preamp goes a long way in a fixed elevation setup. 73 Clayton W5PFG On Dec 17, 2013 7:24 PM, Ted k7trkra...@charter.net wrote: I'm kind of looking for an update from Bob, but can't find his email right now... But the question is, in view of what appears to be some renewed interest in working the new cube sats, et al, is asking Bob to comment on his earlier thoughts on using antennae at fixed elevations. For me, I'm using my Elk on a Rat Shack rotor at a fixed el per Bob's recommendations. (I'm still struggling with PCSAT32...!!!%^*!!) but, this antenna set up is very cost effective and seems to perform pretty well. For example, Joel Black has asked for some advice in an earlier posting. My concern is that new operators or those returning run out and spend a bunch of $$$ on a new setup. No one knows how long the current crop will last or if a new crop is in the future, so probably some caution on the Visa is warranted. Just asking (and especially Bob) 73, Ted K7TRK -Original Message- From: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] On Behalf Of Bob Bruninga Sent: Tuesday, April 12, 2011 8:23 AM To: amsat-bb@AMSAT.Org Subject: [amsat-bb] Re: satellite average elevation we used a horizontally polarized yagi fixed at 30 degrees above the horizon. That worked very well.. Thanks for the confirmation. Yes, elevation rotation is simply not needed at all for LEO spacecraft and modest beams. A mild, fixed tilt modest beam is just perfect. But, the 30 degree angle myth is very pervasive throughout amsat, whereas, the optimum angle is more like 15 degrees. A 30 degree up-tilt gives up too much gain (-3 dB!) on the horizon where signals are weakest and where satellites spend most of their time, and puts the gain in an area of the sky where the satellite is already 6 dB stronger and is rarely there (giving you max beam gain where you need it least). If you look at the sketches on the web page, the optimum angle is more like 15 degrees up-tilt. It preserves max gain on the horizon within 1 dB (where it is needed most) and focuses the breadth of its gain on the area of the sky where the satellites spend something like 95% of their time. For the missing 5%, the satellite is right on top of you and almost 10 dB stronger without any beam at all. Oh, and the 15 degree up-tilt beam is also perfect for Terrestrial operations as well. See the sketch on: http://aprs.org/rotator1.html In some future life, if we ever get back to HEO's and huge OSCAR arrays, then elevation rotors have a place. These high-gain beams have such narrow gain patterns, that higher precision tracking is a must. (Though it is complete overkill for LEO's). Using these OVERKILL arrays for LEO's adds significant complexity to LEO operation requiring higher precision tracking, elevation rotors, better timing, fresher element sets and automated operation. Using a TV rotator and 15 degree fixed tilt beam is much more forgiving... Bob, Wb4APR ___ Sent via AMSAT-BB@amsat.org. 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 ___ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur
[amsat-bb] Re: satellite average elevation new birds
Just a short time ago after I moved into a new shack, I operated for a month with an Elk at 15 degrees on a tripod. Armstrong rotor. I worked all the current satellites right up through the first week we had AO-73's transponder available. Pay close attention to comments WB4APR has made about setting the fixed elevation based on the lowest horizon you can work. For example, if it takes ten degrees for you to clear a mountain, twenty five degrees is probably okay. If you have a clear horizon view, fifteen is probably okay. The goal is to have as much gain available at your lowest elevation to increase your available range. YMMV PS A preamp goes a long way in a fixed elevation setup. 73 Clayton W5PFG On Dec 17, 2013 7:24 PM, Ted k7trkra...@charter.net wrote: I'm kind of looking for an update from Bob, but can't find his email right now... But the question is, in view of what appears to be some renewed interest in working the new cube sats, et al, is asking Bob to comment on his earlier thoughts on using antennae at fixed elevations. For me, I'm using my Elk on a Rat Shack rotor at a fixed el per Bob's recommendations. (I'm still struggling with PCSAT32...!!!%^*!!) but, this antenna set up is very cost effective and seems to perform pretty well. For example, Joel Black has asked for some advice in an earlier posting. My concern is that new operators or those returning run out and spend a bunch of $$$ on a new setup. No one knows how long the current crop will last or if a new crop is in the future, so probably some caution on the Visa is warranted. Just asking (and especially Bob) 73, Ted K7TRK -Original Message- From: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] On Behalf Of Bob Bruninga Sent: Tuesday, April 12, 2011 8:23 AM To: amsat-bb@AMSAT.Org Subject: [amsat-bb] Re: satellite average elevation we used a horizontally polarized yagi fixed at 30 degrees above the horizon. That worked very well.. Thanks for the confirmation. Yes, elevation rotation is simply not needed at all for LEO spacecraft and modest beams. A mild, fixed tilt modest beam is just perfect. But, the 30 degree angle myth is very pervasive throughout amsat, whereas, the optimum angle is more like 15 degrees. A 30 degree up-tilt gives up too much gain (-3 dB!) on the horizon where signals are weakest and where satellites spend most of their time, and puts the gain in an area of the sky where the satellite is already 6 dB stronger and is rarely there (giving you max beam gain where you need it least). If you look at the sketches on the web page, the optimum angle is more like 15 degrees up-tilt. It preserves max gain on the horizon within 1 dB (where it is needed most) and focuses the breadth of its gain on the area of the sky where the satellites spend something like 95% of their time. For the missing 5%, the satellite is right on top of you and almost 10 dB stronger without any beam at all. Oh, and the 15 degree up-tilt beam is also perfect for Terrestrial operations as well. See the sketch on: http://aprs.org/rotator1.html In some future life, if we ever get back to HEO's and huge OSCAR arrays, then elevation rotors have a place. These high-gain beams have such narrow gain patterns, that higher precision tracking is a must. (Though it is complete overkill for LEO's). Using these OVERKILL arrays for LEO's adds significant complexity to LEO operation requiring higher precision tracking, elevation rotors, better timing, fresher element sets and automated operation. Using a TV rotator and 15 degree fixed tilt beam is much more forgiving... Bob, Wb4APR ___ Sent via AMSAT-BB@amsat.org. 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 ___ Sent via AMSAT-BB@amsat.org. 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 ___ Sent via AMSAT-BB@amsat.org. 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
[amsat-bb] Re: satellite average elevation
I saw on this bb a site or note that shows the overall average elevatation. As I remember it elevation is surprisingly low for most passes. Where can I find it? I have a sketch on my web page: http://aprs.org/rotator1.html It shows that 70% of the time LEO satellites are below 12 degrees. The good news is that for the 30% of the time they are above say 12 degrees, they are 6 dB stronger. You can visualize this anytime by recognizing that the radius of the earth is about 4000 miles. And the radius of a LEO satellite is about 4400 miles. So swing an arc on a sheet of paper (the earths surface), and then swing another one only 10% above it (the LEO satellite) and then draw the tangent through your station. It is amazing to see how far away the horizon is and how much time a satellite is way out there... Bob, WB4APR ___ Sent via AMSAT-BB@amsat.org. 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
[amsat-bb] Re: satellite average elevation
Back in the goode olde dayes (i.e. OSCAR VI and OSCAR VII), before elevation rotors were popular, we used a horizontally polarized yagi fixed at 30 degrees above the horizon. That worked very well even for overhead passes. Glen, K9STH Website: http://k9sth.com --- On Tue, 4/12/11, Bob- W7LRD w7...@comcast.net wrote: I saw on this bb a site or note that shows the overall average elevatation. As I remember it elevation is surprisingly low for most passes. Where can I find it? ___ Sent via AMSAT-BB@amsat.org. 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
[amsat-bb] Re: satellite average elevation
we used a horizontally polarized yagi fixed at 30 degrees above the horizon. That worked very well.. Thanks for the confirmation. Yes, elevation rotation is simply not needed at all for LEO spacecraft and modest beams. A mild, fixed tilt modest beam is just perfect. But, the 30 degree angle myth is very pervasive throughout amsat, whereas, the optimum angle is more like 15 degrees. A 30 degree up-tilt gives up too much gain (-3 dB!) on the horizon where signals are weakest and where satellites spend most of their time, and puts the gain in an area of the sky where the satellite is already 6 dB stronger and is rarely there (giving you max beam gain where you need it least). If you look at the sketches on the web page, the optimum angle is more like 15 degrees up-tilt. It preserves max gain on the horizon within 1 dB (where it is needed most) and focuses the breadth of its gain on the area of the sky where the satellites spend something like 95% of their time. For the missing 5%, the satellite is right on top of you and almost 10 dB stronger without any beam at all. Oh, and the 15 degree up-tilt beam is also perfect for Terrestrial operations as well. See the sketch on: http://aprs.org/rotator1.html In some future life, if we ever get back to HEO's and huge OSCAR arrays, then elevation rotors have a place. These high-gain beams have such narrow gain patterns, that higher precision tracking is a must. (Though it is complete overkill for LEO's). Using these OVERKILL arrays for LEO's adds significant complexity to LEO operation requiring higher precision tracking, elevation rotors, better timing, fresher element sets and automated operation. Using a TV rotator and 15 degree fixed tilt beam is much more forgiving... Bob, Wb4APR ___ Sent via AMSAT-BB@amsat.org. 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
[amsat-bb] Re: satellite average elevation
As I said, in the goode olde dayes we used 30 degree up tilt and it worked well... Lessening the up tilt may increase the gain for the lower angle passes but will also decrease the gain on the higher angle passes. So, it is a trade off no matter what you do! Sorry to sound like I am quibbling... but that last sentence implies the idea of an equal trade off. But the tradeoff is not equal at all and may be missing the point here. A LEO satellite pass does not need gain at higher angles because the satellite is by definition 2 or 3 times closer to the ground station (+6 to +9dB stronger). But one does need the gain at lower angles where the satellite is much further away. An up-tilt of 30 degrees is throwing away excess gain where it is not needed (high angles) at the expense of low angles where every single dB -is- needed. So there is no real tradeoff... A lower angle (about 15 degrees) is more-or-less optimum for LEO's with fixed tilt and modest gain beams. To actually quantify the exact best angle (which will depend on the actual beam's own beamwidth), it is simply to up-tilt the antenna no more than the angle at which the gain on the horizon LOSES say less than 1 dB. Note, this is not half the published antenna beamwidth which is usually a 3 dB beamwidth. It is much less than that, less than half the 1 dB beam width. You can measure this by setting the beam no higher than the upangle that loses less than 1 dB to a signal on the horizon Something like that... Bob, WB4APR ___ Sent via AMSAT-BB@amsat.org. 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
[amsat-bb] Re: satellite average elevation
Need to take into account also that the main lobe of a bean even flat on the horizon the max center of the main lobe is still not also dead on the horizon but elevated some due to ground reflections. Joe WB9SBD The Original Rolling Ball Clock Idle Tyme Idle-Tyme.com http://www.idle-tyme.com On 4/12/2011 1:24 PM, Bob Bruninga wrote: X-Antispam: NO; Spamcatcher 6.1.2. Score 1 As I said, in the goode olde dayes we used 30 degree up tilt and it worked well... Lessening the up tilt may increase the gain for the lower angle passes but will also decrease the gain on the higher angle passes. So, it is a trade off no matter what you do! Sorry to sound like I am quibbling... but that last sentence implies the idea of an equal trade off. But the tradeoff is not equal at all and may be missing the point here. A LEO satellite pass does not need gain at higher angles because the satellite is by definition 2 or 3 times closer to the ground station (+6 to +9dB stronger). But one does need the gain at lower angles where the satellite is much further away. An up-tilt of 30 degrees is throwing away excess gain where it is not needed (high angles) at the expense of low angles where every single dB -is- needed. So there is no real tradeoff... A lower angle (about 15 degrees) is more-or-less optimum for LEO's with fixed tilt and modest gain beams. To actually quantify the exact best angle (which will depend on the actual beam's own beamwidth), it is simply to up-tilt the antenna no more than the angle at which the gain on the horizon LOSES say less than 1 dB. Note, this is not half the published antenna beamwidth which is usually a 3 dB beamwidth. It is much less than that, less than half the 1 dB beam width. You can measure this by setting the beam no higher than the upangle that loses less than 1 dB to a signal on the horizon Something like that... Bob, WB4APR ___ Sent via AMSAT-BB@amsat.org. 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 ___ Sent via AMSAT-BB@amsat.org. 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
[amsat-bb] Re: satellite average elevation
Okay---but the 12-15 degree argument _assumes_ that the station has a view to the horizon that isn't tainted by trees, hills, and houses. In those circumstances, 30 deg might well be the better choice! I know it would be where my array is at currently. So, the 12-15 degree optimum assumes a clear view to the horizon...right?? Mark N8MH On Tue, Apr 12, 2011 at 2:24 PM, Bob Bruninga bruni...@usna.edu wrote: As I said, in the goode olde dayes we used 30 degree up tilt and it worked well... Lessening the up tilt may increase the gain for the lower angle passes but will also decrease the gain on the higher angle passes. So, it is a trade off no matter what you do! Sorry to sound like I am quibbling... but that last sentence implies the idea of an equal trade off. But the tradeoff is not equal at all and may be missing the point here. A LEO satellite pass does not need gain at higher angles because the satellite is by definition 2 or 3 times closer to the ground station (+6 to +9dB stronger). But one does need the gain at lower angles where the satellite is much further away. An up-tilt of 30 degrees is throwing away excess gain where it is not needed (high angles) at the expense of low angles where every single dB -is- needed. So there is no real tradeoff... A lower angle (about 15 degrees) is more-or-less optimum for LEO's with fixed tilt and modest gain beams. To actually quantify the exact best angle (which will depend on the actual beam's own beamwidth), it is simply to up-tilt the antenna no more than the angle at which the gain on the horizon LOSES say less than 1 dB. Note, this is not half the published antenna beamwidth which is usually a 3 dB beamwidth. It is much less than that, less than half the 1 dB beam width. You can measure this by setting the beam no higher than the upangle that loses less than 1 dB to a signal on the horizon Something like that... Bob, WB4APR ___ Sent via AMSAT-BB@amsat.org. 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 -- Mark L. Hammond [N8MH] ___ Sent via AMSAT-BB@amsat.org. 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
[amsat-bb] Re: satellite average elevation
Gentlemen, Your difference of opinion may stem from the fact that AO-6 through AO-8 had orbits that were in the 1450km range, and not the 600-800km that is more common now. That might hose up the numbers some, as the angles and path losses are considerably different. You just might be _BOTH_ right for the assumed scenario. 73, Drew KO4MA -Original Message- From: Bob Bruninga bruni...@usna.edu Sent: Apr 12, 2011 2:24 PM To: amsat-bb@amsat.org Subject: [amsat-bb] Re: satellite average elevation As I said, in the goode olde dayes we used 30 degree up tilt and it worked well... Lessening the up tilt may increase the gain for the lower angle passes but will also decrease the gain on the higher angle passes. So, it is a trade off no matter what you do! Sorry to sound like I am quibbling... but that last sentence implies the idea of an equal trade off. But the tradeoff is not equal at all and may be missing the point here. ___ Sent via AMSAT-BB@amsat.org. 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
[amsat-bb] Re: satellite average elevation
Okay---but the 12-15 degree argument _assumes that the station has a view to the horizon that isn't tainted by trees, hills, and houses. In those circumstances, 30 deg might well be the better choice!... So, the 12-15 degree optimum assumes a clear view to the horizon...right?? Yes. Correct. But if one cannot see nor hear below 20 degrees, such a station is missing out on almost 70% of all the times a LEO satellite is above the horizon anyway. In that case, then there is little justification for even having a beam, motors, tracking, and timing and a PC at all. At 30 degrees and above, signals from LEO's are 5 dB or more stronger than at the horizon, and a simple 1/4 wave whip over a ground plane (with a pre-amp) will just about hear everything with no moving parts or tracking. If you want even more gain, make the whip 3/4 wavelength long (still 19.5 at UHF) and get nearly 7 dB antenna gain in a cone above 30 degrees. That plus the 5 dB closeness gives you at least 10 dB gain over what a vertical will hear of a satellite on the horizon. But you are correct. If you really want to have a beam and you really want to have motors and tracking, and PC's and updated elements, etc, then I DO AGREE, tilting up to have the main lobe just over the tops of the visible horizon is an improvement. TO be clear. I am not arguing against a specific angle (say 30) just because its 30, but I am arguing against how the choice of that angle is presented. If it is presented in the absence of an appreciation of the significant 4 to 1 difference in signal power over the angles from 30 down to 0.. or does not reference the 1 to 4 times increase in VISIBILITY DURATION over that same drop in angle, then I think it is worth pointing out. I can see now that I should add a plot of visibility time versus angle as well as the path-gain vs angle on the web page: http://aprs.org/rotator1.html By the way, that is an old page, and you can ignore the how to build a TV rotor controlled station, since no softare currently drives it except mine (obsolete). But the information on the geometery of LEO passes is what most satellite newbee's overlook. Bob, WB4APR Mark N8MH On Tue, Apr 12, 2011 at 2:24 PM, Bob Bruninga bruni...@usna.edu wrote: As I said, in the goode olde dayes we used 30 degree up tilt and it worked well... Lessening the up tilt may increase the gain for the lower angle passes but will also decrease the gain on the higher angle passes. So, it is a trade off no matter what you do! Sorry to sound like I am quibbling... but that last sentence implies the idea of an equal trade off. But the tradeoff is not equal at all and may be missing the point here. A LEO satellite pass does not need gain at higher angles because the satellite is by definition 2 or 3 times closer to the ground station (+6 to +9dB stronger). But one does need the gain at lower angles where the satellite is much further away. An up-tilt of 30 degrees is throwing away excess gain where it is not needed (high angles) at the expense of low angles where every single dB -is- needed. So there is no real tradeoff... A lower angle (about 15 degrees) is more-or-less optimum for LEO's with fixed tilt and modest gain beams. To actually quantify the exact best angle (which will depend on the actual beam's own beamwidth), it is simply to up-tilt the antenna no more than the angle at which the gain on the horizon LOSES say less than 1 dB. Note, this is not half the published antenna beamwidth which is usually a 3 dB beamwidth. It is much less than that, less than half the 1 dB beam width. You can measure this by setting the beam no higher than the upangle that loses less than 1 dB to a signal on the horizon Something like that... Bob, WB4APR ___ Sent via AMSAT-BB@amsat.org. 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 ___ Sent via AMSAT-BB@amsat.org. 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
[amsat-bb] Re: satellite average elevation
On Tue, Apr 12, 2011 at 3:49 PM, Bob Bruninga bruni...@usna.edu wrote: Okay---but the 12-15 degree argument _assumes that the station has a view to the horizon that isn't tainted by trees, hills, and houses. In those circumstances, 30 deg might well be the better choice!... So, the 12-15 degree optimum assumes a clear view to the horizon...right?? Yes. Correct. But if one cannot see nor hear below 20 degrees, such a station is missing out on almost 70% of all the times a LEO satellite is above the horizon anyway. In that case, then there is little justification for even having a beam, motors, tracking, and timing and a PC at all. On the contrary---all the more reason to get more gain on the uplink and the downlink with directional arrays! It helps with the leaves and trees,and you can work through quite a bit of material--trust me! Mark N8MH At 30 degrees and above, signals from LEO's are 5 dB or more stronger than at the horizon, and a simple 1/4 wave whip over a ground plane (with a pre-amp) will just about hear everything with no moving parts or tracking. If you want even more gain, make the whip 3/4 wavelength long (still 19.5 at UHF) and get nearly 7 dB antenna gain in a cone above 30 degrees. That plus the 5 dB closeness gives you at least 10 dB gain over what a vertical will hear of a satellite on the horizon. But you are correct. If you really want to have a beam and you really want to have motors and tracking, and PC's and updated elements, etc, then I DO AGREE, tilting up to have the main lobe just over the tops of the visible horizon is an improvement. TO be clear. I am not arguing against a specific angle (say 30) just because its 30, but I am arguing against how the choice of that angle is presented. If it is presented in the absence of an appreciation of the significant 4 to 1 difference in signal power over the angles from 30 down to 0.. or does not reference the 1 to 4 times increase in VISIBILITY DURATION over that same drop in angle, then I think it is worth pointing out. I can see now that I should add a plot of visibility time versus angle as well as the path-gain vs angle on the web page: http://aprs.org/rotator1.html By the way, that is an old page, and you can ignore the how to build a TV rotor controlled station, since no softare currently drives it except mine (obsolete). But the information on the geometery of LEO passes is what most satellite newbee's overlook. Bob, WB4APR Mark N8MH On Tue, Apr 12, 2011 at 2:24 PM, Bob Bruninga bruni...@usna.edu wrote: As I said, in the goode olde dayes we used 30 degree up tilt and it worked well... Lessening the up tilt may increase the gain for the lower angle passes but will also decrease the gain on the higher angle passes. So, it is a trade off no matter what you do! Sorry to sound like I am quibbling... but that last sentence implies the idea of an equal trade off. But the tradeoff is not equal at all and may be missing the point here. A LEO satellite pass does not need gain at higher angles because the satellite is by definition 2 or 3 times closer to the ground station (+6 to +9dB stronger). But one does need the gain at lower angles where the satellite is much further away. An up-tilt of 30 degrees is throwing away excess gain where it is not needed (high angles) at the expense of low angles where every single dB -is- needed. So there is no real tradeoff... A lower angle (about 15 degrees) is more-or-less optimum for LEO's with fixed tilt and modest gain beams. To actually quantify the exact best angle (which will depend on the actual beam's own beamwidth), it is simply to up-tilt the antenna no more than the angle at which the gain on the horizon LOSES say less than 1 dB. Note, this is not half the published antenna beamwidth which is usually a 3 dB beamwidth. It is much less than that, less than half the 1 dB beam width. You can measure this by setting the beam no higher than the upangle that loses less than 1 dB to a signal on the horizon Something like that... Bob, WB4APR ___ Sent via AMSAT-BB@amsat.org. 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 -- Mark L. Hammond [N8MH] ___ Sent via AMSAT-BB@amsat.org. 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
[amsat-bb] Re: satellite average elevation
Bob etal, Your discussion has prompted me to throw up a yagi (2m7) quickly in anticipation of ARISSat-1. Viewing ISS from Alaska is much simpler: Just point due south on the horizon as ISS rises no more than 15 deg and usually half that angle. Living near 61 deg N latitude makes the ISS 51 deg maximum sub-satellite longitude very low in the southern sky and at maximum range. I even have a preamp to use. Hoping to capture telemetry. 73, Ed - KL7uW At 11:49 AM 4/12/2011, Bob Bruninga wrote: Okay---but the 12-15 degree argument _assumes that the station has a view to the horizon that isn't tainted by trees, hills, and houses. In those circumstances, 30 deg might well be the better choice!... So, the 12-15 degree optimum assumes a clear view to the horizon...right?? Yes. Correct. But if one cannot see nor hear below 20 degrees, such a station is missing out on almost 70% of all the times a LEO satellite is above the horizon anyway. In that case, then there is little justification for even having a beam, motors, tracking, and timing and a PC at all. At 30 degrees and above, signals from LEO's are 5 dB or more stronger than at the horizon, and a simple 1/4 wave whip over a ground plane (with a pre-amp) will just about hear everything with no moving parts or tracking. If you want even more gain, make the whip 3/4 wavelength long (still 19.5 at UHF) and get nearly 7 dB antenna gain in a cone above 30 degrees. That plus the 5 dB closeness gives you at least 10 dB gain over what a vertical will hear of a satellite on the horizon. But you are correct. If you really want to have a beam and you really want to have motors and tracking, and PC's and updated elements, etc, then I DO AGREE, tilting up to have the main lobe just over the tops of the visible horizon is an improvement. TO be clear. I am not arguing against a specific angle (say 30) just because its 30, but I am arguing against how the choice of that angle is presented. If it is presented in the absence of an appreciation of the significant 4 to 1 difference in signal power over the angles from 30 down to 0.. or does not reference the 1 to 4 times increase in VISIBILITY DURATION over that same drop in angle, then I think it is worth pointing out. I can see now that I should add a plot of visibility time versus angle as well as the path-gain vs angle on the web page: http://aprs.org/rotator1.html By the way, that is an old page, and you can ignore the how to build a TV rotor controlled station, since no softare currently drives it except mine (obsolete). But the information on the geometery of LEO passes is what most satellite newbee's overlook. Bob, WB4APR Mark N8MH On Tue, Apr 12, 2011 at 2:24 PM, Bob Bruninga bruni...@usna.edu wrote: As I said, in the goode olde dayes we used 30 degree up tilt and it worked well... Lessening the up tilt may increase the gain for the lower angle passes but will also decrease the gain on the higher angle passes. So, it is a trade off no matter what you do! Sorry to sound like I am quibbling... but that last sentence implies the idea of an equal trade off. But the tradeoff is not equal at all and may be missing the point here. A LEO satellite pass does not need gain at higher angles because the satellite is by definition 2 or 3 times closer to the ground station (+6 to +9dB stronger). But one does need the gain at lower angles where the satellite is much further away. An up-tilt of 30 degrees is throwing away excess gain where it is not needed (high angles) at the expense of low angles where every single dB -is- needed. So there is no real tradeoff... A lower angle (about 15 degrees) is more-or-less optimum for LEO's with fixed tilt and modest gain beams. To actually quantify the exact best angle (which will depend on the actual beam's own beamwidth), it is simply to up-tilt the antenna no more than the angle at which the gain on the horizon LOSES say less than 1 dB. Note, this is not half the published antenna beamwidth which is usually a 3 dB beamwidth. It is much less than that, less than half the 1 dB beam width. You can measure this by setting the beam no higher than the upangle that loses less than 1 dB to a signal on the horizon Something like that... Bob, WB4APR ___ Sent via AMSAT-BB@amsat.org. 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 ___ Sent via AMSAT-BB@amsat.org. 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 73, Ed - KL7UW, WD2XSH/45 == BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME:
[amsat-bb] Re: satellite average elevation
One thing that I didn't mention is that my house is 1/2 block from the highest point in the city (less than 8 feet in elevation) and it is basically downhill in all directions. My top antenna, on my main tower, is 67 feet above ground and is visible from the freeway about a mile away. Since I have lived in this house longer than anyone else on the street all have purchased their houses knowing that the antennas are there. Several neighbors have told me that if I every sell the house I have to leave the towers! It seems the towers are the landmark by which they tell people how to find their house! Glen, K9STH Website: http://k9sth.com ___ Sent via AMSAT-BB@amsat.org. 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
[amsat-bb] Re: satellite average elevation
- Original Message - From: Glen Zook gz...@yahoo.com To: amsat-bb@amsat.org; Bob Bruninga bruni...@usna.edu Sent: Tuesday, April 12, 2011 10:39 PM Subject: [amsat-bb] Re: satellite average elevation Again, back in those dayes we did not have the luxury of computer simulation and from trial and error the majority of people found that about 30 degrees above the horizontal worked the best. That is why the olde tymers recommend 30 degrees. It worked very well and we made many contacts using the LEO satellites. Glen, K9STH Hi Glen, K9STH In those days of OSCAR-6 we did not have the luxury of a PC but we used the OSCARLOCATOR.By the way for best performance on OSCAR-6 ,OSCAR-7 and OSCAR-8 an elevation motor was required and the most popular for elevation was a KR-500 allowing manual elevation traking and flipping when necessary. A 30 degrees elevation for the antennas was seldom used with OSCAR-6 ,7 and 8 resulting in marginal performance. With the actual LEO satellites like VO-52 , AO-51 and FO-29 the altitude is much lower and according to Bob Bruniga demonstration a fixed elevation of 15 to 20 degrees seems to be a good compromise but obviously using an elevation motor is much better. 73 de i8CVS Domenico ___ Sent via AMSAT-BB@amsat.org. 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
[amsat-bb] Re: satellite average elevation
Somewhere I still have an OSCAR locator. That is why several locals came up with a computer program to run on a mainframe to calculate the elevation and compile a set of tables. MUCH easier! Glen, K9STH Website: http://k9sth.com --- On Tue, 4/12/11, i8cvs domenico.i8...@tin.it wrote: From: i8cvs domenico.i8...@tin.it Subject: Re: [amsat-bb] Re: satellite average elevation To: Glen Zook gz...@yahoo.com, Amsat - BBs amsat-bb@amsat.org, Bob Bruninga bruni...@usna.edu Date: Tuesday, April 12, 2011, 10:32 PM - Original Message - From: Glen Zook gz...@yahoo.com To: amsat-bb@amsat.org; Bob Bruninga bruni...@usna.edu Sent: Tuesday, April 12, 2011 10:39 PM Subject: [amsat-bb] Re: satellite average elevation Again, back in those dayes we did not have the luxury of computer simulation and from trial and error the majority of people found that about 30 degrees above the horizontal worked the best. That is why the olde tymers recommend 30 degrees. It worked very well and we made many contacts using the LEO satellites. Glen, K9STH Hi Glen, K9STH In those days of OSCAR-6 we did not have the luxury of a PC but we used the OSCARLOCATOR.By the way for best performance on OSCAR-6 ,OSCAR-7 and OSCAR-8 an elevation motor was required and the most popular for elevation was a KR-500 allowing manual elevation traking and flipping when necessary. A 30 degrees elevation for the antennas was seldom used with OSCAR-6 ,7 and 8 resulting in marginal performance. With the actual LEO satellites like VO-52 , AO-51 and FO-29 the altitude is much lower and according to Bob Bruniga demonstration a fixed elevation of 15 to 20 degrees seems to be a good compromise but obviously using an elevation motor is much better. 73 de i8CVS Domenico ___ Sent via AMSAT-BB@amsat.org. 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
