Social Feed
I took some time off from redeploying my dishes to look over a nagging problem I had called USALS. Last year I tossed a 1.2 m GEOSATpro on the roof with a PowerTech DG-380 motor. It was easy to tweak and I soon had it tracking the Clarke belt over the motor's range.
My true south is about 105 degrees, allowing me to get most of the Ku action not too far off-center. From the beginning I noticed when using my Pansat 9200HD, the farther I drove the dish from center in either direction, the greater the in-track error in positioning. In fact both east and west errors were about the same for similar offsets, with the Pansat always driving the dish not quite far enough. I realized this might simply be accumulating mechanical errors in the motor, but the consistency was concerning. In reality this wasn't causing any real trouble, because orbital locations 45 degrees from my true south were experiencing only about a 0.2 degree error. This could be easily compensated by lying to the Pansat about the orbital location. However the error quickly got larger for the lower elevation birds.
We had high winds a few weeks ago that blew the 1.2 m mount slightly off. When resetting the adjustments I again verified the satellites far off-center only had in-track errors (ie. bumping the dish up or down only reduced the signal level). I got curious what was going on. As far as I can tell, the USALS algorithms have not been openly published. There were a handful of website calculators that made some or all of the calculations, but none agreed for significant offset angles, and none agreed with my Pansat's calculated motor angles. I also looked through a number of open-source codes for controlling USALS motors, and that only increased the cacophony.
I surmised the discrepancies might have to do with different declination offset angles, and further reading found many approaches to calculating the 'optimal' declination offset angle. Of course none were the same. As the declination offset is only an approximate correction to track the arc, it appeared the differences probably resulted from different optimization criteria. For example, one approximation might minimize the tracking error for angles close to true south, at the expense of angles close to the horizon. Another might do the opposite.
Rather than re-derive each approach and figure out where they made different assumptions, I thought this was prime territory for a little linear algebra. For fun I decided to employ a non-spherical earth model and consider my altitude (this turned out to be useless for Denver because its altitude essentially offsets the earth's polar flattening). Fairly quickly I found the Pansat calculated motor angles were precisely in agreement with a zero declination offset angle, other than when it tried to calculate orbital positions more than about 65 degrees from true south and got completely nonsensical answers.
I then set up my calculations to optimize cross-track performance by varying the declination offset angle. This was all fun and good, but not terribly practical because there were many excellent fits using different optimization criteria with maximum cross-track errors of a few-thousandths of a degree. Satellites typically are only kept positioned in a box much bigger than that, even considering the folly of thinking one could adjust a dish to that accuracy.
Nevertheless to put theory into practice I hauled up the theodolite and tweaked everything until I got bored. One of the open-source programs I had come across is called xdipo and with one of my USB receivers was an excellent starting point for a better USALS controller than the Pansat. xdipo's calculations for motor offset angles are way off, but that can be fixed. I modified a number of xdipo's controls and tweaked its display of the signal levels and quality to make it into a more precise tuning instrument. It's rather convenient because the USB receiver is inside the house run by a Linux machine running xdipo remotely over wireless to display on my laptop on the roof. In some ways this turned out to be more precise than using a spectrum analyzer, and a lot faster. It didn't take long to confirm my direct calculations of the motor angle were dead-on for the given declination angle, while the Pansat was not. I was also able to calibrate out an error in the DG-380's view of what was a zero offset angle by subtracting this out in xdipo. I haven't taken the DG-380 apart, but I would like to remove this mechanical error.
I'm confident the Pansat is making the simplifying assumption that there is no declination offset angle, causing the positioning error to increase with angle. One could partially compensate for this mechanically through an intentional misalignment, at the expense of cross-track error. That wouldn't make a lot of sense.
I can't change the Pansat USALS calculations, but I could write code for Linux to build an accurate satellite positioning system. I've put that in my project to-do hopper because the Pansat has other limitations with positioning that I am no longer willing to tolerate. Whether these same approximations/errors exist in other receivers I cannot say, but hopefully some of what I've come across may explain oddities others have observed.
My true south is about 105 degrees, allowing me to get most of the Ku action not too far off-center. From the beginning I noticed when using my Pansat 9200HD, the farther I drove the dish from center in either direction, the greater the in-track error in positioning. In fact both east and west errors were about the same for similar offsets, with the Pansat always driving the dish not quite far enough. I realized this might simply be accumulating mechanical errors in the motor, but the consistency was concerning. In reality this wasn't causing any real trouble, because orbital locations 45 degrees from my true south were experiencing only about a 0.2 degree error. This could be easily compensated by lying to the Pansat about the orbital location. However the error quickly got larger for the lower elevation birds.
We had high winds a few weeks ago that blew the 1.2 m mount slightly off. When resetting the adjustments I again verified the satellites far off-center only had in-track errors (ie. bumping the dish up or down only reduced the signal level). I got curious what was going on. As far as I can tell, the USALS algorithms have not been openly published. There were a handful of website calculators that made some or all of the calculations, but none agreed for significant offset angles, and none agreed with my Pansat's calculated motor angles. I also looked through a number of open-source codes for controlling USALS motors, and that only increased the cacophony.
I surmised the discrepancies might have to do with different declination offset angles, and further reading found many approaches to calculating the 'optimal' declination offset angle. Of course none were the same. As the declination offset is only an approximate correction to track the arc, it appeared the differences probably resulted from different optimization criteria. For example, one approximation might minimize the tracking error for angles close to true south, at the expense of angles close to the horizon. Another might do the opposite.
Rather than re-derive each approach and figure out where they made different assumptions, I thought this was prime territory for a little linear algebra. For fun I decided to employ a non-spherical earth model and consider my altitude (this turned out to be useless for Denver because its altitude essentially offsets the earth's polar flattening). Fairly quickly I found the Pansat calculated motor angles were precisely in agreement with a zero declination offset angle, other than when it tried to calculate orbital positions more than about 65 degrees from true south and got completely nonsensical answers.
I then set up my calculations to optimize cross-track performance by varying the declination offset angle. This was all fun and good, but not terribly practical because there were many excellent fits using different optimization criteria with maximum cross-track errors of a few-thousandths of a degree. Satellites typically are only kept positioned in a box much bigger than that, even considering the folly of thinking one could adjust a dish to that accuracy.
Nevertheless to put theory into practice I hauled up the theodolite and tweaked everything until I got bored. One of the open-source programs I had come across is called xdipo and with one of my USB receivers was an excellent starting point for a better USALS controller than the Pansat. xdipo's calculations for motor offset angles are way off, but that can be fixed. I modified a number of xdipo's controls and tweaked its display of the signal levels and quality to make it into a more precise tuning instrument. It's rather convenient because the USB receiver is inside the house run by a Linux machine running xdipo remotely over wireless to display on my laptop on the roof. In some ways this turned out to be more precise than using a spectrum analyzer, and a lot faster. It didn't take long to confirm my direct calculations of the motor angle were dead-on for the given declination angle, while the Pansat was not. I was also able to calibrate out an error in the DG-380's view of what was a zero offset angle by subtracting this out in xdipo. I haven't taken the DG-380 apart, but I would like to remove this mechanical error.
I'm confident the Pansat is making the simplifying assumption that there is no declination offset angle, causing the positioning error to increase with angle. One could partially compensate for this mechanically through an intentional misalignment, at the expense of cross-track error. That wouldn't make a lot of sense.
I can't change the Pansat USALS calculations, but I could write code for Linux to build an accurate satellite positioning system. I've put that in my project to-do hopper because the Pansat has other limitations with positioning that I am no longer willing to tolerate. Whether these same approximations/errors exist in other receivers I cannot say, but hopefully some of what I've come across may explain oddities others have observed.
39 Replies
·
13384 views
A
This may be an old thread, but I read it some time ago and found it very interesting, and very puzzling at the same time, because back then I didn't understand a lot of it I must confess.
However now I understand quite a bit more, and maybe can add some usefull info.
The calculated rotation angles for a motor axis parallel to the earth polar axis is also called Hour Angle in some calculators.
(Hour angles are also the base for calculating LNB-distances for multifeed-rails on satellite dishes, by the way.)
For calculating angles for the adjusted motor angles, using a polar axis tilt, I had the following thought:
With a tilted rotation axis, the "equator" of the rotation gets lower than the earth equator, to exactly the amount of degrees of the axis tilt.
So with calculating the adjusted Hour Angles, the axis tilt value has to be added to the value of the latitude angle, used in the formula for the Hour Angle.
All the other variables in the formula can then remain the same.
I put this way of calculating in a spreadsheet, an got results only some hundredth degrees different from the values of pendragon and B.J.
So my way of calculating must be accurate enough, I would say.
The latitude alteration would also be the way to trick the 'normal' USALS Hour Angle calculation of a receiver, I think.
Add the difference of the "normal" motor elevation and the used "adjusted" motor elevation to the latitude value in the receiver, and you get the "adjusted" hour angle (which is then sent to the motor).
(You can also use the difference between the "normal" declination angle and the used "adjusted" declination angle; that is of course the same value.)
I compared the values of the normal hour angle and the adjusted hour angle for some earth coordinates and a range of satellites, and the difference between them was never more than 0.07 degrees, I'm afraid. I had expected bigger differences.
However maybe for hard to get satellites it might be of help, to use this adjusted latitude value.
greetz,
A33
Edit: BTW, I 've never seen tested that a USALS calculation of a receiver actually sends the diseqc command corresponding to the hour angle (that is the rotation angle when using a motor axis parallel to the earth polar axis). Has anyone tested this, with a diseqc command reader or oscilloscope or other measuring instrument?
This may be an old thread, but I read it some time ago and found it very interesting, and very puzzling at the same time, because back then I didn't understand a lot of it I must confess.
However now I understand quite a bit more, and maybe can add some usefull info.
The calculated rotation angles for a motor axis parallel to the earth polar axis is also called Hour Angle in some calculators.
(Hour angles are also the base for calculating LNB-distances for multifeed-rails on satellite dishes, by the way.)
For calculating angles for the adjusted motor angles, using a polar axis tilt, I had the following thought:
With a tilted rotation axis, the "equator" of the rotation gets lower than the earth equator, to exactly the amount of degrees of the axis tilt.
So with calculating the adjusted Hour Angles, the axis tilt value has to be added to the value of the latitude angle, used in the formula for the Hour Angle.
All the other variables in the formula can then remain the same.
I put this way of calculating in a spreadsheet, an got results only some hundredth degrees different from the values of pendragon and B.J.
So my way of calculating must be accurate enough, I would say.
The latitude alteration would also be the way to trick the 'normal' USALS Hour Angle calculation of a receiver, I think.
Add the difference of the "normal" motor elevation and the used "adjusted" motor elevation to the latitude value in the receiver, and you get the "adjusted" hour angle (which is then sent to the motor).
(You can also use the difference between the "normal" declination angle and the used "adjusted" declination angle; that is of course the same value.)
I compared the values of the normal hour angle and the adjusted hour angle for some earth coordinates and a range of satellites, and the difference between them was never more than 0.07 degrees, I'm afraid. I had expected bigger differences.
However maybe for hard to get satellites it might be of help, to use this adjusted latitude value.
greetz,
A33
Edit: BTW, I 've never seen tested that a USALS calculation of a receiver actually sends the diseqc command corresponding to the hour angle (that is the rotation angle when using a motor axis parallel to the earth polar axis). Has anyone tested this, with a diseqc command reader or oscilloscope or other measuring instrument?
Altitude should not make a difference to USALS calculations, at least not enough of a difference to change settings. If you needed accuracy to less than 1/10th of a degree then maybe... Consider how far away the satellite is and if it moved a mile up, down, left, or right, it wouldn't make a change in reception.
However... as you mentioned sunburning your head.. there is less atmosphere up there than at sea level so signals to the horizon should be better than lower down in elevation. If you are on a mountaintop then you might even squeek in a half or a degree or more off your horizon... but at 5000ft not much of a difference.
However... as you mentioned sunburning your head.. there is less atmosphere up there than at sea level so signals to the horizon should be better than lower down in elevation. If you are on a mountaintop then you might even squeek in a half or a degree or more off your horizon... but at 5000ft not much of a difference.
Supporting Founder
Lifetime Supporter
This thread is a place to discuss the 4K events that appear on channel 540. We are getting, at this point, one college football game a week. Let's hope there is more coming.
1928 Replies
·
298785 views
Hmmm, I'm not seeing anything like those events in our Hopper 3 guide for tonight or Saturday.
I went into the Tools menu and requested a Guide Update. I'll try looking at it after the update completes.
For quite a while now, people with a VIP211k have been losing their recordings on their activated external HDDs... even when there's nothing physically wrong with HDD. I believe this is an intentional and underhanded tactic that Dish is pulling in an attempt to force users away from the VIP211k.
They are obviously regretting that they ever let users have a "non-dvr" dvr in the first place. You would think they would be happy charging you a $40 one time fee... and then be happy letting the customer be the one responsible for HDD failures.
Dish clearly hates the 211k bitter-clingers. This recording deletion problem is intentional (IMO), and I think it is just one more tool that they are using. Hopper and a 2-year agreement... that's what they want you to have. Think about that... a 2-year agreement... with a company $30 Billion in debt (that's with a B). What happens when all that debt causes them to drop the channel that may have been your whole reason for having Dish in the first place? Guess who's stuck with a service that no longer suits their needs... for the remainder of the 2-year agreement.
On top of that, they don't want you to install it yourself. I purchased and installed all my equipment myself. That used to be common. Now, they lie to me and tell me that my dish must be updated to use a Hopper. Funny thing is... they don't even know what dish I have because they didn't install it, and I didn't tell them. If you ask what type of dish/LNBs the hopper needs... good luck getting an answer. All they know is that whatever you have needs to be upgraded by an installer.
It is quite apparent to me that they care much more about staying in their box, than they do working with the customer. That's too bad, because it hasn't always been that way. It's like they are totally unaware of the current business environment that they are trying to compete in.
I have been a customer since 2010. I will be cancelling my service before the next period. Yeah, I know, my $1,200 a year won't make a difference to them. It just seems like they have forgotten who needs who, especially when you consider the competition in today's streaming world. But hey, they will have succeed in forcing me off the 211k.
They are obviously regretting that they ever let users have a "non-dvr" dvr in the first place. You would think they would be happy charging you a $40 one time fee... and then be happy letting the customer be the one responsible for HDD failures.
Dish clearly hates the 211k bitter-clingers. This recording deletion problem is intentional (IMO), and I think it is just one more tool that they are using. Hopper and a 2-year agreement... that's what they want you to have. Think about that... a 2-year agreement... with a company $30 Billion in debt (that's with a B). What happens when all that debt causes them to drop the channel that may have been your whole reason for having Dish in the first place? Guess who's stuck with a service that no longer suits their needs... for the remainder of the 2-year agreement.
On top of that, they don't want you to install it yourself. I purchased and installed all my equipment myself. That used to be common. Now, they lie to me and tell me that my dish must be updated to use a Hopper. Funny thing is... they don't even know what dish I have because they didn't install it, and I didn't tell them. If you ask what type of dish/LNBs the hopper needs... good luck getting an answer. All they know is that whatever you have needs to be upgraded by an installer.
It is quite apparent to me that they care much more about staying in their box, than they do working with the customer. That's too bad, because it hasn't always been that way. It's like they are totally unaware of the current business environment that they are trying to compete in.
I have been a customer since 2010. I will be cancelling my service before the next period. Yeah, I know, my $1,200 a year won't make a difference to them. It just seems like they have forgotten who needs who, especially when you consider the competition in today's streaming world. But hey, they will have succeed in forcing me off the 211k.
164 Replies
·
7280 views
Staff member
HERE TO HELP YOU!
Cutting Edge
Sometimes a thread gets so many posts in it that is can cause issues for the server so that why today we introduce The Song Name Game Part 3!
So let the game continue!
The last song was added by Bobby who posted...
One Meat Ball - Andrews Sisters
CONTINUE ON AND HAVE FUN! WELCOME HOME TO SATELLITEGUYS.US!
Here are the original rules for the game as posted by WebbyDude back in 2006. http://www.satelliteguys.us/threads/68645-Song-Name-Game
Just name a song title and the band who performed it. The next person does the same thing, but needs to list a song title or band name which includes a word from the previous entry. Pick songs from any genre.
Example:
Long Live Rock and Roll -- Rainbow
Rainbow in the Dark -- Dio
Another example:
Ride the Lightning -- Metallica
Lightning Strikes -- Ozzy Osbourne
Get it?
An additional note: we all know that song titles, sometimes, use profane words. Because this is a family friendly website it is advised that you clean up that title up a bit. This is accomplished by using something like sh!t instead of the real word. Thanks....
So let the game continue!
The last song was added by Bobby who posted...
One Meat Ball - Andrews Sisters
CONTINUE ON AND HAVE FUN! WELCOME HOME TO SATELLITEGUYS.US!
Here are the original rules for the game as posted by WebbyDude back in 2006. http://www.satelliteguys.us/threads/68645-Song-Name-Game
Just name a song title and the band who performed it. The next person does the same thing, but needs to list a song title or band name which includes a word from the previous entry. Pick songs from any genre.
Example:
Long Live Rock and Roll -- Rainbow
Rainbow in the Dark -- Dio
Another example:
Ride the Lightning -- Metallica
Lightning Strikes -- Ozzy Osbourne
Get it?
An additional note: we all know that song titles, sometimes, use profane words. Because this is a family friendly website it is advised that you clean up that title up a bit. This is accomplished by using something like sh!t instead of the real word. Thanks....
68493 Replies
·
2670153 views
Staff member
HERE TO HELP YOU!
Hard getting used to the new younger Gibbs, Mark Harmons son had the right look but I understand he didn't want the role.
Still I'm enjoying, pretty good job with Franks.
Still I'm enjoying, pretty good job with Franks.
63 Replies
·
4177 views
Mark Harmon is coming back as Gibbs in Origins, for the full season. Just saw, Dinozzo too, on NCIS . That will be an interesting writing project.
deadline.com
Mark Harmon Returning To 'NCIS: Origins' As Gibbs For Season 3
Mark Harmon is returning to NCIS: Origins for a season-long arc.
deadline.com
Supporting Founder
Really excited for this season with Kentucky having a new coach and some really exciting recruits. Probably won't last long, but here's hoping this season is great.
136 Replies
·
1300 views
College Football Playoff nears agreement on 24-team expansion that could end title games
The College Football Playoff field is about to get much more crowded as the conferences near a deal to double the size of the field to 24 teams starting next year
www.cbssports.com
Pub Member / Supporter
Lifetime Supporter
Can't help but wonder if a worker overlooked checking the harness. I rarely ride a roller coaster anymore but when I do I check the harness myself pretty aggressively.
Can't imagine what the son is going through.
www.dailymail.com
Can't imagine what the son is going through.
Dad levitated and bled then fell to his death from coaster
Eyewitnesses have shared fresh details of the horrific accident that happened at Six Flags Over Georgia on Monday afternoon.
24 Replies
·
193 views
Could B&M’s Patent on the “Clamshell” Ride Restraint Design Offer Clues as to What Happened on Goliath at Six Flags Over Georgia?
Incredibly sad news out of Six Flags Over Georgia as it’s being reported one man was killed after being ejected from Goliath, the B&M hyper coaster. Many news outlets have posted pictures of pe…
bgtsafari.com
Had no idea there were that many redundancies built into those restraints.Could B&M’s Patent on the “Clamshell” Ride Restraint Design Offer Clues as to What Happened on Goliath at Six Flags Over Georgia?
Incredibly sad news out of Six Flags Over Georgia as it’s being reported one man was killed after being ejected from Goliath, the B&M hyper coaster. Many news outlets have posted pictures of pe…
It makes sense, however, I would want more types of restraints, so if one doesn't work, the other does ... the restraints coming over the shoulder I would have expected ... with a Seat belt as last resort.
Fwiw, I inquired with what they use on Coasters at Cedar Point, various Coasters, different restraints according to what the car and track requires ...
NONE of the Coasters at CP use THAT particular system
I'm glad to see ...
Lifetime Supporter
Schedule drops tomorrow. Mandatory mini camps in June. Hall of Fame game August 6th.
108 Replies
·
1558 views
Y
Browns lose a close one with... The Jets. That is a classic Browns loss (granted, any loss is a classic one it seems). 49'ers, Vikings, and Chiefs remain undefeated. The AFC north have a three way tie at 3-2 for second place.
A big win for the Patriots, and they are now 3-2.
Browns lose a close one with... The Jets. That is a classic Browns loss (granted, any loss is a classic one it seems). 49'ers, Vikings, and Chiefs remain undefeated. The AFC north have a three way tie at 3-2 for second place.
Troy Aikman seems to confirm he'll be leaving ESPN
Aikman says he looks forward to "where my next landing spot will be."
www.nbcsports.com
M
Hopefully nowhere near a microphone.Troy Aikman seems to confirm he'll be leaving ESPN
Aikman says he looks forward to "where my next landing spot will be."
Pub Member / Supporter
Lifetime Supporter
Wasn't exactly sure where to post this. Just had a customer come in inquiring about internet. He has HughesNet and had heard good things about mine. He asked if we provided email addresses and it kinda caught me off guard. I said he should be able to keep whatever email he had been using....my sister in law is still using a BellSouth email addy and they haven't been around here for many years. He said he had gotten a letter from HughesNet stating that they had until Nov 16th to save, move, forward, whatever, their Hughesnet emails because they would lose them after that date.
I have never heard of a company simply mass-deleting email accounts (the customer still has his HughesNet service). From what I understand, in the past, the company who was ditching their email service simply sold the customer base to a company like Google.
Anyone else getting this letter. He said he would show it to me tomorrow when I go out there and set up his internet.
I have never heard of a company simply mass-deleting email accounts (the customer still has his HughesNet service). From what I understand, in the past, the company who was ditching their email service simply sold the customer base to a company like Google.
Anyone else getting this letter. He said he would show it to me tomorrow when I go out there and set up his internet.
6 Replies
·
94 views
Still the same number of years, just more Sunsets…Wouldn't we then die of old age sooner?
Anyone else watch this show? Any guesses as to what was in the box Gibbs gave to Abby that was on her desk? It look liked it was glowing.
I also heard that someone was leaving the show at the end of this season. Any guesses as to who thats going to be?
I also heard that someone was leaving the show at the end of this season. Any guesses as to who thats going to be?
2130 Replies
·
214633 views
Tony as the director.
Would you rather have LaRoche ???Tony as the director.
OTHER Mini Multiswitch
I just received 6 receiver 2 port mini Multiswitch and it work great, no external power need it, and you can connect 6 receiver instead of 4 on most Mini Multiswitches... If anyone is interested in where they can get one PM me....
3 Replies
·
59 views
