Declination adjestment question

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LocutusOfBorg

LocutusOfBorg

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Original poster
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Aug 2, 2009
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The manufacturers manual for both my KTI and Paraclipse shows a declination of 5.8 degrees for my latitude while online sources show 6.5. Which is correct? My latitude is 42 degrees. A formula from Polar Dish Mount works out to 6.5 degrees. How can both manuals differ so much from online info (including the sticky in this section)?
 
Titanium said:
There are standard and adjusted declination tables. The adjusted declination table provides improved tracking on the edges of the arc.
Click to expand...

Unless the table is marked, which one is which? By the way, I'm talking about polar mount declination, not magnetic declination.
 
If the chart's listed mount angle is the same as your latitude, it is the standard declination chart. If the mount angle is not equal to your latitude, it is the modified declination chart.

Mount angle + Declination angle = Apex of Arc

The standard declination table uses your latitude as the mount angle plus the declination angle to equal the required dish elevation angle to track the arc. The modified declination chart subtracts a declination angle from the required dish angle to equal the mount angle.
 
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Modified angles means: forward axis tilt (no longer parallel to earth axis).
That means that the declination offset angle (due south/north) must be set smaller, than with traditional motor angles.

So in your case, 42*N: modified motor axis elevation should be 47.35* (instead of 48*),
and declination offset angle 5.85* (instead of 6.5*).

Total dish elevation (due south) = 41.5*.

Greetz,
A33
 
I guess I'm not explaining myself very well. All these sources that I'm mentioning are about aligning a TVRO polar mount such as my KTI and Paraclipse. According to the manuals for those antennas, my mount elevation angle is set for the latitude and the declination offset for 5.8 degrees which results in a zenith angle of 47.8 degrees. Online sources say that my declination offset angle should be 6.5 degrees. I don't know which declination angle to use. Since I have set the declination according to the manuals, I'm having trouble picking up sats on the ends of the arc. But, before I go experimenting, I'd like to know what the declination offset angle should be. I'm assuming that all TVRO polar mounts are adjusted the same - set the mount elevation angle and then the declination offset angle. From what I've seen, the spacers that I use for declination causes the antenna to point downward (toward the horizon). When I adjust the KTI declination rods, the reflector is moved downward also. Take a peek at page 4 of the Bud manual in the C-band sticky thread - it says 6.5 degree declination.
 
Evidently, we crossed eachother, posting (see above).

Beware, however, when you use the modified declination offset angle, you should also use the modified motor axis elevation angle!
Or else you would mis-align....

greetz,
A33
 
Why does this have to be so complicated and confusing? I'll just follow the manufacturers info and hope for the best.
 
johnnynobody said:
Why does this have to be so complicated and confusing? I'll just follow the manufacturers info and hope for the best.
Click to expand...


Johnny, that info is just to get you into the ballpark!

After you set that up, you have to fine tune it by either raising or lowering the dish by hand and observing which way the signal gets better.

Then you have to rotate your dish on the pole accordingly!

I do not have a link to post, but I am sure that someone here will post one for you soon!

To be clear, you will be doing this on the ends of the arc where you are having trouble!
 
johnnynobody said:
Why does this have to be so complicated and confusing?
Click to expand...

What is complicated and confusing?

When you use the 'traditional' setup angles, you'll need time-consuming finetuning afterwards, and hopefully you'll end near perfect. So the first setup is just "quick and dirty". That is because the used rotation axis of that setup is not matched to following the 'ellips' of the clarke belt.
Use the 'modified' setup angles, and you'll end near perfect immediately, because with that angles you do in fact follow the clarke belt 'ellips'. The theory behind it is sound.
(The clarke belt, of course, is a circle. But seen from any location on earth, not coinciding with the polar axis, it forms an ellips.)

What is in fact confusing, is that not many people understand this method, or believe it can be calculated, as they are used to the finetuning afterwards.
I myself would invest in the setting up along the modified angles. The exact measuring costs a little time, but saves a lot of time afterwards.


If you like reading, see e.g.: Traditional vs Modified Elevation/Declination Angles
and the link to this forum USALS Notebook is also very informative.


greetz,
A33
 
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a33 said:
What is complicated and confusing?
Click to expand...

When you have instructions that say the declination should be 5.8 while a few others say 6.5, it's confusing. And there are installation instructions that say don't mess (fine tune) with the elevation/declination after finding and peaking elevation at the "highest" satellite while other instructions say it's OK to fine tune those settings after tuning in the satellites by rotating the mount at the low ends of the arc. By the way, why do declination settings tables go down to hundredths of a degree when most inclinometers don't have that detail. Why don't the tables round to the nearest tenth of a degree? And does it matter if you set the declination for 5.8 instead of the table setting of 5.85? I suppose that there are inclinometers that give digital readouts to hundredths or even thousandths of a degree but I'm sure they'd be quite expensive and probably have to have a lab certification for accuracy.
 
Ah, yes, multiple ways are described about (fine)tuning a dish, and it is hard to decide which method would be best, if no explanation is given as to why that method would be better than another. (I wouldn't know the best way, either!)

But it is good that you asked here about the (modified) angles, and I hope that part is cleared by now.


About the hundredths of a degree: You are right that for measurement that is a bit ambitious/unrealistic.
However if you use a table and you have to find an intermediate value, it is good that you can use the precise theoretical values. You can then do the rounding yourself.

And another reason why I like very precise angle-data in any table, is that I can deduct (re-calculate) from that what method is used to calculate the outcome: for instance which value for earth radius is used (6371 (mean) or 6378 (at equator), alas I see the latter rather often), what motor-hourangle value is used (traditional, or 'modified'), and if a method that I am trying leads to exactly that value or just 'about' that value (e.g. dish skew for multifeed setups, that is still a little project for me).
So all the decimals make a table much more informative for 'research'.:)


I hope with the new modified angles, you can track the arc better now?

Greetz,
A33
 
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johnnynobody said:
Why does this have to be so complicated and confusing? I'll just follow the manufacturers info and hope for the best.
Click to expand...

I recently picked up a 12 foot Unimesh. According to the chart, my elevation was supposed to set at 39.65. It did not track until I set the elevation to 40.3 and then figured in the offset angle for my location. Now, it tracks perfectly.
 
Titanium said:
Mount elevation plus declination angle equals satellite arc. If the pole is not plumb, mount or dish is distorted, then this may not be true...
Click to expand...

I left everything set the way it was when I picked up the 12 footer thinking it would work since it's original location was about 5 mile as the crow flies from my house. It didn't work of course. You know the old saying about assuming. :(
 
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Progress report. I set the declination as closely to 5.8 as possible. Found loose hardware on one of the declination rods, BTW. I did the initial peaking at the top of the arc. I found it interesting that after tightening down the mount bolts after adjusting azimuth that the C/N dropped 3 dB. Re-adjusting the elevation, not azimuth, fixed that issue. So far the tracking looks good +/- 12 degrees. Hopefully, I'll find another decent day to work on the viewable edges of the arc even though there's not much TV of interest beyond what I can already see.

However, one of the problems with using DiseqC 1.2 is that if your dish mover (i.e. Gbox) is remotely located you don't know if the dish is moving since you don't get a pulse count display on your TV screen. You may have told your STB to go a position but there's no guarantee that the antenna is going to move or is actually moving. That has been a "gotcha" for me several times. Sometimes it takes my Gbox about a minute before it'll move the dish to the requested position, if it moves the dish at all. I have heard that there are new receivers and dish movers that use a newer DiseqC standard that will give a true dish moving indication. I guess most people have their STB and dish mover in the same room as their TV? But, I gotta be different. I'd rather have both the STB and dish mover remoted to cut down on cable clutter in the family room.
 
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johnnynobody said:
Progress report. I set the declination as closely to 5.8 as possible. Found loose hardware on one of the declination rods, BTW. I did the initial peaking at the top of the arc. I found it interesting that after tightening down the mount bolts after adjusting azimuth that the C/N dropped 3 dB. Re-adjusting the elevation, not azimuth, fixed that issue. So far the tracking looks good +/- 12 degrees. Hopefully, I'll find another decent day to work on the viewable edges of the arc even though there's not much TV of interest beyond what I can already see.

However, one of the problems with using DiseqC 1.2 is that if your dish mover (i.e. Gbox) is remotely located you don't know if the dish is moving since you don't get a pulse count display on your TV screen. You may have told your STB to go a position but there's no guarantee that the antenna is going to move or is actually moving. That has been a "gotcha" for me several times. Sometimes it takes my Gbox about a minute before it'll move the dish to the requested position, if it moves the dish at all. I have heard that there are new receivers and dish movers that use a newer DiseqC standard that will give a true dish moving indication. I guess most people have their STB and dish mover in the same room as their TV? But, I gotta be different. I'd rather have both the STB and dish mover remoted to cut down on cable clutter in the family room.
Click to expand...

On my old 10ft Perfect Ten dish with 24" ball-screw Venture actuator and Vbox 10, you can't even hear the dish move when standing right next to it. That dish was taken down, and is sitting behind my shed at the new house we moved to, I don't have the space here to reinstall one that large. The Vbox was in the tv entertainment center where I could see the display.
 
johnnynobody said:
When you have instructions that say the declination should be 5.8 while a few others say 6.5, it's confusing. And there are installation instructions that say don't mess (fine tune) with the elevation/declination after finding and peaking elevation at the "highest" satellite while other instructions say it's OK to fine tune those settings after tuning in the satellites by rotating the mount at the low ends of the arc. By the way, why do declination settings tables go down to hundredths of a degree when most inclinometers don't have that detail. Why don't the tables round to the nearest tenth of a degree? And does it matter if you set the declination for 5.8 instead of the table setting of 5.85? I suppose that there are inclinometers that give digital readouts to hundredths or even thousandths of a degree but I'm sure they'd be quite expensive and probably have to have a lab certification for accuracy.
Click to expand...

You can buy an inclinometer off ebay that will measure hundreths for about $50. I have two inclinometers. Once cost me $350, the other $50, and when checked against each other, they produce the same readings. I just got into that with a dish I installed. I ended up with an elevation of 40.31. Set it on the mark, along with the offset of course, and it tracks perfectly.

The chart I was using said it should have been set at 39.63, but it would not track properly at that elevation.
 
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