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?
73 Bob W7LRD
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
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 w7lrd@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?
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
As I said, in the "goode olde dayes" we used 30 degree up tilt and it worked well for all passes including overhead passes. 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!
Of course, back in the early 1970s we did not have computer simulations of antenna patterns, etc. readily available and experimentation showed that 30 degrees worked the best.
In terms of computers, if one had use of a computer what was generally done was to take the "keps" of a particular satellite (then primarily OSCAR VI and OSCAR VII) and make tables showing the azimuth and elevation for passes at various equator crossings giving a relative time for AOS and LOS. You just added this time to the actual "clock" time and adjusted your rotor direction to correspond with this.
During the early 1970s, members of the Richardson Wireless Klub (K5RWK - Richardson, Texas) had access to main frame computers at Collins Radio, Texas Instruments, and Electrospace that were used to compute the information. This information was compiled into a set of tables for OSCAR VI and OSCAR VII which was applicable to a radius of around 100 miles from the Dallas / Fort Worth area.
Using this rudimentary information I was able to acquire the 1st Satellite 1000 award issued in the 5th call area and the 3rd award issued anywhere. Also was able to acquire the achievement recognition number 32. Many of today's operators are not aware of the efforts that it took "back then" to work the satellites. Computer control of antennas, doppler, etc., make things much easier these days.
Glen, K9STH AMSAT 239/LM 463
Website: http://k9sth.com
--- On Tue, 4/12/11, Bob Bruninga bruninga@usna.edu wrote:
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).
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
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
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 bruninga@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
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 bruninga@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
On Tue, Apr 12, 2011 at 3:49 PM, Bob Bruninga bruninga@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 bruninga@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
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
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 bruninga@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: 144-1.4kw, 432-100w, 1296-testing*, 3400-winter? DUBUS Magazine USA Rep dubususa@hotmail.com ======================================
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.
After a relatively short time (less than a year), I acquired an Alliance TV rotor and used it as an elevation rotor along with an AR-22 for the azimuth rotor.
Frankly, even in "those dayes" the antennas often had more than enough gain to make it into the satellites. In fact, AMSAT was pleading with people to reduce their transmitting power to keep the linear transponders from overloading on a single signal which would allow many more people to use the satellites at the same time.
One could use a computer to determine the vertical pattern of their antenna and then determine exactly the elevation that is optimum for their antenna. That angle might be something like 17.2345 degrees, it might be something like 10.795 degrees, or, depending on the design it could be considerably greater. There are many variables and determining the optimum angle is going to be difficult.
Back when AMSAT was formed, and well into its life, people were experimenting to find what worked and what did not work. Back then, the majority of people found that about 30 degrees above the horizontal worked well and that became the defacto standard for a fixed elevation. If computer simulation now proves otherwise then so be it.
Whether the operator puts his/her beam at 15 degrees elevation, at 30 degrees elevation, or at another elevation, the answer to the original question remains the same. Yes, using a yagi with a fixed elevation can be used for satellite communication and, in the vast majority of time, a fixed elevation yagi works very well.
As for measuring a true 1 dB that takes some fairly good test equipment. The "S" meter on most equipment these days is not calibrated to the old standard of S-9 = 50 microvolts, 6 dB per "S" unit, etc. With 50 microvolts for S-9 a 20 dB over signal requires 500 microvolts, a 40 dB over signal requires 5,000 microvolts and a 60 dB over signal requires 50,000 microvolts.
Since I am in the business (am retired but "fix" a lot of radios for others), I have had the chance to actually measure "S" meter readings. A goodly number of "modern" radios read S-9 at around 10 microvolts, 20 dB over at around 40 microvolts, 40 dB over at around 100 microvolts. The dB of signal between "S" units varies all over the place.
The reason that S-9 = 50 microvolts is not used is because a while back the various manufacturers got into a "war" claiming that "their" receivers were "more sensitive" than the next manufacturers. However, what the manufacturers did was to reduce the signal strength required for an S-9 reading and to change the "dB over" readings into signal levels that don't even come close to being accurate.
An "S" meter can be used to determine relative signal strengths such as whether or not one antenna is working better under similar conditions. But, unless the actual meter readings have been accurately calibrated using an accurate standard, or if a calibrated attenuator is placed in the signal path, then there is absolutely no way of telling just how much stronger the signal is from one source to another.
FM "S" meters actually read limiter current and not actual signal strength. Since limiters are designed to saturate at a relatively low signal strength, an FM "S" meter reading will increase very rapidly with small signal increases. Then, upon saturation, there will be very little increase in the reading. A limiter is designed to remove any AM component from the signal leave only the FM or PM signal to be demodulated. That is why FM/PM (most of the older "FM" equipment was actually PM - phase modulated) is much less bothered by noise than an AM signal (SSB and CW are AM modes) since noise is amplitude modulated and not frequency or phase modulated.
Glen, K9STH
Website: http://k9sth.com
--- On Tue, 4/12/11, Bob Bruninga bruninga@usna.edu wrote:
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....
----- Original Message ----- From: "Glen Zook" gzook@yahoo.com To: amsat-bb@amsat.org; "Bob Bruninga" bruninga@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
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.i8cvs@tin.it wrote:
From: i8cvs domenico.i8cvs@tin.it Subject: Re: [amsat-bb] Re: satellite average elevation To: "Glen Zook" gzook@yahoo.com, "Amsat - BBs" amsat-bb@amsat.org, "Bob Bruninga" bruninga@usna.edu Date: Tuesday, April 12, 2011, 10:32 PM ----- Original Message ----- From: "Glen Zook" gzook@yahoo.com To: amsat-bb@amsat.org; "Bob Bruninga" bruninga@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
"Whether the operator puts his/her beam at 15 degrees elevation, at 30 degrees elevation, or at another elevation, the answer to the original question remains the same. Yes, using a yagi with a fixed elevation can be used for satellite communication and, in the vast majority of time, a fixed elevation yagi works very well."
Well said, Glen. After all the discussion I put my Elk up at somewhere between 30 and 25 and it works like a champ !! Night and day over my previous circular set up !! I'm not losing any sleep over +- 5 degrees...
73, Ted K7TRK
participants (8)
-
Bob Bruninga -
Bob- W7LRD -
Edward R. Cole -
Glen Zook -
i8cvs -
Joe -
Mark L. Hammond -
Ted