Calculate elevation screw degrees

[Anole]

If you decide to put in a fine-tuning screw to adjust elevation, it would be nice to estimate how many turns per degree it gives you.
Shown, are two recent designs from some of our more industrious members.
They use a tuning bolt, or a piece of all thread rod.
Since I don't have the actual numbers from the members who made them, I'll have to guess.

The same idea applies to adjusting the elevation or declination on C-band dishes, if you have the dimensions and do the math right.

There are several ways to skin this cat.
Biggest problem is making a generalized table which won't apply exactly to your situation.
However, the table below is a fair approximation, and should be good enough, so long as...
... the distance from the pivot to the screw is several times longer than the screw distance.

  [FONT=Courier New]n = distance of pivot bolt to adjustment screw
  s = distance of the screw (assumed to be 1 for this table)
  i = degrees movement per inch of screw travel
  t = degrees movement per turn, given 20 turns per inch screw
tpi = turns per inch
T/º = Turns to go one degree, approx

 n      i        t       T/º
---   ----     ----     -----
 2    30º      1.50º
 3    19.5º    0.97º     1T/º
 4    14.5º    0.72º
 5    11.5º    0.57º
 6     9.6º    0.48º     2T/º
 7     8.2º    0.41º
 8     7.2º    0.36º
 9     6.4º    0.32º     3T/º
10     5.7º    0.286º
11     5.1º    0.26º     4T/º
---------------------[/FONT]

The actual math is:

sin-1(0.5s/n) X 2 = i
i / tpi = t

 

[Hermitman]

I'm all for experimentation in the hobby but I think I'd rather use a c-band method and translate that to the smaller, offset ku dishes. On the big dishes, I use a protractor and adustment screw to find and set elevation and declination settings. For the smaller, offset dishes, I would compute the offset angle of the dish, determine the elevation required and then use a protractor against the flat mounting plate on the back of the dish to set the elevation. The adjustment screw would be used to maintain that postition. But to each their own. The fun part of this hobby is finding out the many different ways you can use just to see a picture from a satellite.

 

[patmos]

I've got a 120cm Eurostar(same as fortec) and I find it difficult to fine tune. This is a good idea. I am not using a motor. Is there any modification to be made to this set up?

 

[Anole]

The picture of the big Fortec dish above, was the project of member JsatTV.
He first described the problem and some ideas were worked out in this thread.
Then, he later returned to discuss results of the modification.

If I had his dimensions from his unit, I might be able to make a better estimate of how accurately his fine-tuning screw works.

 

[patmos]

would the screw be slanting like the photos? I understand this as per the mathematical triangle. My dish is fix and I only want to have more than one turn per degree. I am thinking to bend the back plate to allow the slant movement.

 

[Anole]

Having more distance between the PIVOT point and each end of the screw is what makes for fine adjustment.
OR, a finer pitched screw will naturally do the same.

If you can give the distance from the pivot point to EACH end of the screw, I'll try to calculate the approximate fine tuning rate.
And by 'end of the screw', I really mean where it attaches to the two pieces, of course.
Must have the number of turns of the screw to go an inch or centimeter or whatever the metric equivalent is for screws, if applicable.
For instance, a common US bolt or threaded rod would be 1/4-20.
That means 1/4 inch diameter, and 20 turns to move one inch.

 

[patmos]

I'll try to get this measurement when the climate is better.Should both n be equal? As I see in the given pic. Since the screw is straight, the elevation will be limited.If I could move up to 75 deg it would be fine. To do this the pivot point of the screw on the backplate will be lower and by the same time S will increase and the n to the right decrease. The backplate need to be shorter.The mathematical formula wont hold good. All this I'm only guessing. For my case even if it is not precise , fine tuning would be good.

 

[Anole]

"close" counts in handgrenades, horseshoes, and satellite fine tuning

The table shown only works for s=1 (screw length of one unit)
and both values of n being equal.
(n1 and n2 might be better names)
That's why I drew the path of the screw between two points on the pictures where n1 = n2.

As s becomes closer to n, the error increases in the table, but can be reasonably calculated as a custom table.
The real world geometry won't match the idealized (and simplified) math, so if n1 and n2 are quite different, we'll take the shorter value, and do the math, and come close enough.

After all, the whole idea is to just get a seat-of-the-pants idea how were doing.
Not calculate to the 3rd decimal digit!

 

[patmos]

I took the measurements when dish is in lowest position. n1=16cm, n2=14cm and s=19cm. the backplate cannot be too high to cater for higher elevation. I measure one inch of threaded rod (ceiling kit/andrew) and got 16 turns.

 

[Anole]

let's get you close

Since your screw pitch was in inches, I converted the other measurements to inches.
n1 = 6.3 inch; n2 = 5.5 inch; screw length = 7.5 inch
then, I assumed n1 = n2 = 6 inch
1/2 screw length = 3.75 inch
sin-1( 3.75/6) = 38.68º for half the screw length
2 X 38.68 = 77.36º for whole screw length
77.36 / 7.5 inch length of the screw / 16 turns per inch = 0.644º per turn

I hope I got that right.
And except for the difference between your 16 TPI screw and the 20 TPI screw in my table in the first post, both are close to half a degree per turn for n=6.

No, this is not a perfect answer, but it at least gives you a rough idea.
Also, since that looks like a commercial mount, I'll wager you could look it up on the manufacturers web site and get the exact answer.

 

[patmos]

Thank you Anole. I'm on the implementation side now.

 

[jsattv]

The picture of the big Fortec dish above, was the project of member JsatTV.
He first described the problem and some ideas were worked out in this thread.
Then, he later returned to discuss results of the modification.

If I had his dimensions from his unit, I might be able to make a better estimate of how accurately his fine-tuning screw works.

Anole, the dimensions of the Plate are 4.75 x 12.75 inches. Hope this helps.

 

[Anole]

Anole, the dimensions of the Plate are 4.75 x 12.75 inches. Hope this helps.

See my marked-up picture of your dish in the first post of this thread.
Tell me how long n is from the pivot bolt up to where your screw goes through the original white brace.
Also, roughly how long is s, say just betweeen the jam nuts will do.
And I'll need the pitch of your screw. Is it 1/4-20 as I described above?
I can calculate your approximate degree per turn, or turns per degree.

 

[patmos]

The bird is not tame

Anole here are some pics of my modification. Very happy but could not catch the bird ( PAS 10 here). Could not get a signal. Will try to get help from more experience friends. The fine tuning is very good. It took a long time to move between 55 and 65 deg.

 

[Anole]

Patmos -

I was confused by your earlier words and pictures.
NOW, these pictures make a lot of sense!
Pretty good job! Congratulations. :up

There is no substitute for experience in looking for a satellite.
The adjustments are delicate, and the receiver needs to be tuned for the new bird ahead of time.
If you haven't done it before, you might want to look at some of the threads here on the forum, where people did it for the first time.
Or, maybe start a new thread, mention where you are and your equipment, and you can get some personal help locating your satellite.


Wait... aren't you the guy who was wanting to replace his 1.2 m dish with a 1.5m to get a stronger signal?
And I think I suggested a 1.8 m would be less expensive...?
Are you sure the 1.2 will get any signal from Pas 10 ?
... which satellite? by location, please?

 

[patmos]

Wait... aren't you the guy who was wanting to replace his 1.2 m dish with a 1.5m to get a stronger signal?
And I think I suggested a 1.8 m would be less expensive...?
Are you sure the 1.2 will get any signal from Pas 10 ?

You're right it's me. But here dishes are not easily available. I thought I could get a 150 cm but in the end I found a cheap package Eurostar 120 cm and receiver Digital telecom for around $110. I took it for the receiver mainly. PAS 10 is receivable on this size of dish here. My friend has one similar system (120 cm / not Eurostar)and is working more or less ok. We are in fringe area. we have to accept it. I went to his place today. Tuned my receiver on his system and it worked. If need be I will take a bigger dish but I wanted to make this one work first. I was afraid of not getting correct kU lnb/feed for the prime focus.And also this thread http://www.satelliteguys.us/showthread.php?t=32733&page=3&highlight=180+sadounwhere sadoun favors the 120 cm for KU . Forget to give credit to where credit ougt to be. The nice soldering work was done by my friend JOHN MAMAROT. Anole let me tell you , you have taken much patience with me. Thank sir Anole.

 

[jsattv]

See my marked-up picture of your dish in the first post of this thread.
Tell me how long n is from the pivot bolt up to where your screw goes through the original white brace.
Also, roughly how long is s, say just betweeen the jam nuts will do.
And I'll need the pitch of your screw. Is it 1/4-20 as I described above?
I can calculate your approximate degree per turn, or turns per degree.

Anole, had to go up on the roof again since the 100 cm Fortec Dish wasn't tracking properly. It just went out of alignment on its own. So took up the small TV and Sat Receiver and had to slightly adjust the East and West travel of the Dish to get it back in line. Elevation was fine, - just East to West movement was off? Can't figure this out!!

While I was up there I got your requested measurements. n = 6.75 inches, From the Pivot Bolt to the threaded rod = 7.5 inches. Don't know what the pitch of the threaded rod is, but it is not Metric.

Hope this helps, and am wondering why the Alignment from East to West goes out occasionally?

 

[Tron]

Hope this helps, and am wondering why the Alignment from East to West goes out occasionally?

That typically happens when winds blow the dish... Sounds like that's what probably happened.