How much of the belt should a polar mount be able to track?

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dem0nlord

SatelliteGuys Pro
Original poster
Dec 12, 2005
331
5
Central Texas
Just doing some fine tuning here, I'm good to AMC8@139W on the W extreme, could maybe go just a bit farther if there was anything out there. To the E I'm good to PAS3R/6B@43W. I still have some jack retraction left to get to at least NSS806@40.5W, which is at about 20 degrees elevation for me, but I can't seem to find it. I do have the international feed for the circular polarity. I know I'm a channel junkie, just wanting to get them because I know they are up there, but am I expecting the unreasonable? Also, what should the skew be set to on circular birds?
 
That's a good question, but there's not an easy answer. I suppose it really depends on the dish. For example, I have an old 10' fiberglass dish, and it's very heavy. It's set-up for a western arc. I'm at 83.8w, and it will flop over at 72.0w, so I rarely go past 83.0w. One time it bent a 24" actuator arm. I also have a 10' mesh dish, it will go further, but I'm not sure how much further. I only go as far as 72.0w with it, as I'm gun shy with the flopping. And that's about as far as I care to go for my C-band, and I have a ku motorized dish I can go further with for ku signals. The mesh will also flop, but it's been so long I can't remember how far it got before the flop.
I've never tried any Circular C-band feeds, so I can't help with that, sorry.

Al
 
With a jack arm assembly, I can usually get a dish on the east coast (74 to 76 deg longitude) to travel from about 139 which is around 15 degrees above the horizon, to around 60 degrees. Because you are in Texas, your western most satellite will be higher in the sky and your eastern satellites will be lower than mine are, but the arc between them will stay about the same.

You can't extend the range of a jaxk arm driven polar movement by using a longer jack arm, but you can extend it by relocating the jack arm clamp mount attachment point away from where it is now. To do this, someone who can picture what I am describing would have to weld a 1/2" plate with a 1/2" hole drilled in it onto the plate that your jackarm attaches to presently. If you bring the mount to a welder and explain to him what you are trying to accomplish, he probably will see what I mean and do it for less than a hundred bucks.
 
Mike yeah I already understand all of that, what I'm asking is there normally some point toward the extreme limits where the polar mount just won't stay on the arc, and hence can't see the satellite? In my case 139 and 45 are both booming, so is my true south at 97, they don't want anything different for elevation, I've tried, so this tells me that the dish should be oriented on the pole correctly, and I should have my elevation and declination correct. 43 is a bit weak, probably wanting an elevation change, and 40.5 just is nobody home. If there was anything to look at to the west, I'd bet they would act the same. Seems that when I start trying to go below 23 degrees elevation, I start missing the arc. I suspect that I'm just being greedy and am after more mechanical accuracy than is available to me from the mount, just wondering if others have run into this at low elevations.
 
...what I'm asking is there normally some point toward the extreme limits where the polar mount just won't stay on the arc, and hence can't see the satellite?
There is no point at which it leaves the arc IF the azimuth and elevation have been set accurately.

Do you have a squacker or any other kind of signal meter? If so, then disconnect the jack arm and peak it at the lowest satellite on the horizon you can see to the west, and then swing it all the way over and it should be a bullseye to the lowest in the east (which may be difficult to do if the only ones at either extreme are circular only but you don't have a circular feed) If you can't peak both from the same mount settings then either your elevation is off or your declination is off..

The maximum tracking error anywhere along the arc using a modified polar mount should only be about a tenth of a degree.

Have you tried to conceptualize how polar tracking works? The satellites are in a circle. If you put a dish on a vertical mast on the north pole with no declination angle, it would sweep out a plane parallel to the equatorial plane and hit nothing, but if you tilt the mast forward, the intersection of the two planes would be a straight line.

So instead, we introduce a declination angle that results in the generation of a cone that exactly intersects the Clark Belt. But it only tracks perfectly if it is on the north or south pole.

In real life, we are tracking from points that are closer to the belt section we are trying to track than is the north pole, so if we set up our mast at exactly our elevation angle and set a declination angle that intersects with the southernmost satellite, then that mount would track to the inside of, or underside of, the arc, because the intersection circle would be smaller than the Clarke belt, but if we instead set a declination angle equal to the real declination angle to the western-most visible satellite, then we would track above the Clarke belt, so the best compromise is to set the dish at the declination angle that corresponds to the lowest satellite on the horizon but when it gets to the top of the arc, fudge the elevation angle to get a bullseye there.

You need to precisely affirm and set your elevation angle and you need to use the so-called "modified polar mount" declination angle rather than the southern intercept declination angle.

I maintain a horizon to horizon mount for a government contractor that designs specialty receivers, and we have no trouble maintaining virtual bulls-eye aim from horizon to horizon using a cheap junk Radio Shack modified polar mount.
 
Well after much adjustment tonight I think I have it. Everything got adjusted multiple times other than I never did have to turn the mount on the pole. I think it was mostly too much declination. It now tracks 37.5W-139W, and that's all it can do, I have only 2 clicks left to the E, and 5 to the W. 37.5 was a surprise, I thought a tree was going to be in the way at only 17.1 elevation. If it's not perfect now, it's damned close.

BTW, on 40.5 skew adjustment does make quite a difference.
 
I think mathematically you can show that the belt can be tracked with the right angle settings. I was going to try to do that but it seemed like so much work that I put it off longer than it took you to actually do it. In any case it's interesting to know that you accomplished it. Good point on the skew. I know that as my dish moves, the feed horn orientation "rotates" and that I need different skew settings across the arc.
 
Oh I forgot to mention, actually going up to a 36" jack without any changes to my mount would give me some more range, since I had to move my current 24" in the clamp some to get it where it is now, the mount can certainly move more in either direction. But it would gain me nothing, the big tree is going to get in the way if I try going more E, and to the W there is nothing there anyway. I'm not about to cut down a 30' tree that gives much needed summer shade to my house just so I can get to 30W at best probably. If Hispasat 1C/1D ever becomes that important to me, I'll just stick up a fixed Ku dish on the roof.
 
I think mathematically you can show that the belt can be tracked with the right angle settings. ...

But it can't be tracked perfectly except from the north and south poles. When you introduce a declination angle into a polar mount, the region swept out is a cone. As you may remember from introductory calculus, the intersection of a cone and a plane is an ellipse. The intersection with a plane perpendicular to the cone's center axis is a circle (a circle can also be called a "degenerate ellipse", meaning one with a distance of zero between its foci).

The Clarke Belt is a circle with a radius of, as I recall, about 26,300 miles. A dish mounted on a polar mount on the north or south poles can be given a declination angle that will generate that exact circle, but when you move the polar axis away from the geosynchronous arcs centerline, there is no circle that can be generated from that point that matches it. The best you can do is generate an ellipse that most closely tracks it, which we approach by constructing an ellipse that touches it at the southern azimuth and the lowest azimuth on either horizon.

Back when I had more time on my hands, I actually made some drawings that showed most of this, and I even had a computer program written in BASIC from an algorithm I devised that could calculate the exact point at which the Clarke Belt dropped below the horizon (my best friend has studied BASIC under Professor John Kemeny at Dartmouth, so I didn't have to work out the snags by myself)
 
i need clarification

how can a longer arm make you see a larger range? i thought your arm extends to the west end of the range. Longer arm means going farther west? I think i have the opposite problem. I can keep going east until it is pointing at the ground, but going west i stop too early. Im still stuck. Are you saying that the true south sat doesn't have to be at the dish's zenith? I can't get rid of the sparklies on all my west satellites. tho when i didn't have a working actuator i could manually move all the settings-azimuth, elev. and declination, to work on each sat individually without the sparkles. Also can't get the reciever to auto peak cause of (severe?) misalignment. Through an accident every now and then i can get it to auto peak, but i'll have it on the ok picture and then hit auto peak and it may end up with a stronger signal on the meter, but the picture is worse, mostly horrible. Shame. i mean, all i see is clear beautiful sky. In the east my power supply that goes from the pole to the house is there, but i can't see anything over there anyway. The trees in my yard and the neighbors yard are all behind the dish, out of the way.
Anyone know how much it costs on average to get someone to come out and tune it for me? I am just about ready to give up...maybe i have TI or something. Maybe im too close to the house. I need a spectral analysis! maybe i can take demonlord hostage to my cheap pasadena home :p
 
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I say a longer jack would give me more range because the polar mount has more range than my jack does. If I loosen the jack clamp and let it slide, the dish can still move more to the east or west. What I did last night was fully extend the jack, then slide it back through the clamp until it was just to the W of 139 before re-tightening it. If my jack was longer I could slide it as far back in the clamp as it will go, that way when fully retracted it would be farther E than now, but when extended would be farther W than now also.

In your case, it does sound like you could move your jack clamp some so that it gives you more W travel, and less E. Work on that dish alignment first though. :D
 
Anyone know how much it costs on average to get someone to come out and tune it for me? I am just about ready to give up...maybe i have TI or something.
You should be able to get the dish peaked for maybe $200. If you really are getting blasted by TI, you probably should abandon the dish, because the tech probably won't have much expertise at remedying it, and even if he knows how, you might not be willing to apy the price.
 
Im still stuck. Are you saying that the true south sat doesn't have to be at the dish's zenith?
No it doesn't, but it helps if it is. The main thing is to have the Polar Mount pointing at True South/True North, and not at your True South Satellite that might be 2 degrees (more or less) off of True South. Most People don't live directly in the path for a True South Satellite. Most People are slightly off alignment from there True South Satellite. It's called a Polar Mount, because it points at the Poles (South and North).
I can't get rid of the sparklies on all my west satellites. tho when i didn't have a working actuator i could manually move all the settings-azimuth, elev. and declination, to work on each sat individually without the sparkles. Also can't get the reciever to auto peak cause of (severe?) misalignment.
I think your biggest problem is, as you say, Misalignment. Have you checked to see if the Pole is Plumb? Another thing that might cause Sparklies, is the LNB (or LNA if that's what you have), my original BUD had a 120 degree LNA on it. When I upgraded to a 100 degree LNB, the picture improved quite noticeably. But I still had a Sparkly problem at times, especially with Red and/or Blue colors. When I upgraded to a 40 degree LNB, the Sparklies disappeared. I think your problem is most likely, an alignment problem. Good Luck!

Al
 
But I still had a Sparkly problem at times, especially with Red and/or Blue colors. When I upgraded to a 40 degree LNB, the Sparklies disappeared. I think your problem is most likely, an alignment problem. Good Luck!

Al

Wow thanks for your input! Yeah, that seems to be the case when i feel i had it at its best, only bright blues and reds showed sparklies. Im not sure how old my cal-amp 20 deg is. Plus i broke the little lnb cover during shipping. I was thinking about getting a Norsat, but i have a fairly small budget for extra things, so I'm needing to maintain the house and cars first, then i was hoping for 4dtv first, then FTA, then the corotor II, then new C and KU lnbs. Maybe one thing a month or something. Im starting with next month a new 4dtv from skyvision and will get cabling and supplies that i need (aww crap its valentines next month -- further delay! Wife wants the Nintendo Wii )
Thanks again
My range of recievable stuff is 72E to 135W. Don't think anything is analog receivable past 72? Even then there is one color bar test on channel three or five @ 72 that just says johnston TV in the middle.
 
My range of recievable stuff is 72E to 135W. Don't think anything is analog receivable past 72? Even then there is one color bar test on channel three or five @ 72 that just says johnston TV in the middle.

I think you wanted to say going east you can hit 72W and going west you can hit 135W :)

Here in Montreal I can hit from 37.5W-139W I have a 24" Venture arm, my dish can go more to the east but my house block the line of site, I am sure if my dish was solid I would get Hispasat looking at half house and half sky :)
 
I think you wanted to say going east you can hit 72W and going west you can hit 135W :)

Here in Montreal I can hit from 37.5W-139W I have a 24" Venture arm, my dish can go more to the east but my house block the line of site, I am sure if my dish was solid I would get Hispasat looking at half house and half sky :)

:haha very true, unless im looking round the world? Wow All the way up there you can see that far??? Wow. You have that thing on a 20 foot pole? Just kidding, but I never get how people work on the cband antennas that where that high up. There are two that i can have (they are in the family and said sure) but i have no idea how to get that high up behind the house. Im afraid to put an extension ladder's top rung on a little pole. Even then what do i dismantle?....

When the neighbors asked about mine, and i told them a little of the pros and cons, and they always seem to really want one (don't think any of them would actually knock on peoples doors like i suggested). Two more potential customers on my street but i can't get the high ones down.... ones i think around 8.5 feet mesh and the other mesh, oh seven i think..seems bigger than 6, but its not like mine. Sucks the industry suffered, people want em, but they aren't going to put a ton of effort into it. The house next to the customer im starting monday has a huge dish farm going. Looks like two 30-something inch World systems, one smaller starchoice wide offset, and one 10 foot cband. the cband antenna is one of those that looks like the picture in the skyvision magazine, the old timey one on the cover of that book that says "skyvision recommended" thats not round. But it has a bellows boot and everything, square post and is located on the very top of his garage apartment behind his house. Way up there. Minimal rust. i love it. You guys must think im obsessed, huh? I'll calm down after a couple of years!
 
My pole is only about 8' I can do all the work on my dish with a small latter.

If you help people get dishes and they are looking to get 4dtv try to get no dishes under 8.5' bigger always being better.
 
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