Converting AZ-El mount to Non-motorised polar mount

[SEOShamsher]

Hi everyone,


I am in the process of converting my existing fixed dish mount into a non-motorised polar mount. I am getting it fabricated by a local welder with my own assistance.I am handling all the accuracy, calculations and angles myself while the welder handles the metalwork.


My location:Latitude: 30.86568° NLongitude: 75.84964° E(Ludhiana, Punjab, India)


Target arc: 4°W to 154°E (4 W at 0° elevation and 154 at 1.5° elevation)


The whole idea of this build is that once the polar axis is set correctly, I only need to rotate the dish left or right on a single axis to point at any satellite across the entire arc.no touching elevation, no touching azimuth ever again. Simple and effective.


My calculated settings:


True south → 178.1° on magnetic compass (corrected for magnetic declination = true 180°)First axis — polar axis tilt → 30.87° above horizon (equal to my site latitude)Second axis — declination offset → 6.7° below polar axis toward equatorCentre reference satellite → 75°E (compass 179.8° — almost perfect true south from my longitude)


I am confident in my calculations. My main concern is real-world accuracy after accurate fabrication and whether small errors compound at the far ends of such a wide arc.

---

My questions for experienced members:

1. Is my understanding correct — that after setting these two angles once during fabrication, I simply rotate the dish left or right on the polar axis to reach any satellite from 4°W all the way to 154°E with zero other adjustment?
2. Is there any natural geometric error that builds up at extreme arc edges (4°W and 154°E) even with a perfectly set polar axis — meaning a small elevation tweak may still be needed at the limits regardless of how accurate the build is?
3. Do professional factory-made polar mounts perform significantly better than a careful DIY fabricated one, or does it all come down to mechanical build precision and correct angles?
4. Do even professional installers find that wide arcs like mine need minor tweaking at the far east and far west limits, or does a correctly aligned polar axis track perfectly end to end?
5. My biggest concern — if after installation I discover a small pointing error at 154°E or 4°W and physically adjust the dish tilt to compensate, will that destroy my centre calibration for satellites near 75°E? Is there any way to correct edge errors without disturbing the centre?
6. Any tips for getting accurate angles during the welding fabrication process — tools, methods, or tricks to ensure the polar axis and declination offset are welded at exactly the right angles?

Thanks to anyone with hands-on experience with wide arc polar mounts or DIY fabrication. Really appreciate any guidance before I commit to welding!

 

[deeptho]

I think it will depend on the size of your dish. I assume you want a big one, otherwise it is much easier
and more practical to use a diseqc rotor. I do not have a really big one, so other people will be able to offer better advice.

But: The same rules apply to a motorized and non-motorized dish, so you can
learn from what people post on the adjustment of USALS rotors, but only for dishes up to 1.2m.

If I remember well, the arc scanned by any polarmount only approximately tracks the geostationary orbit, but
the error remains small and depends on

• how far you are from the equator. Closer is better. Your location is not too bad.
• how big the arc is you want to reach. If your range is 4W - 154W then that is only 30 degrees. Not too extreme.
• how big your dish is. Bigger dishes need more precision.
• If it is C or Ku. Ku needs more precision.

As a point of comparison: I have a 1.2 meter dish, so maybe smaller than what you want, and can track the arc from -30W to 60E with very little
detectable signal loss (0.5 dB ), but this requires

• using "modified" elevation/declination angles. That means finding an optimal compromise between elevation and declination, i.e., using the proper equation. With these angles, the errors in pointing are more evenly distributed between the extremes of the arc and the center of the arc. In other words: these modified angles minimize the worst case error, instead of the error at south. Note that the best compromise will also depend on the arc you want to reach (e.g., different for 30 degrees than for 60)
• very precise adjustment of the ground pole. It needs to be exactly vertical. On a standard adjustable polarmount, elevation can be changed to compensate for non-vertically in north-south direction, but not for east-west errors. On a fixed polar mount neither is impossible.
• So if at all possible, provide some possibility of at least minor adjustments of both elevation, declination, and east-west leaning of the pole. It would be best to have this also on the "polar axis". It can be as simple as some adjustable bolts, but it needs to be easy to handle. Often it is a matter of adjustments of less than 0.5 degree but they can make a big difference.

In any case, I would never try such a thing without providing at least some "minor adjustment" features.

 

[SEOShamsher]

Thank you for the detailed response, really helpful!


Quick clarification question based on what you said about USALS adjustment:


My understanding is that on a polar mount, the arc curve is mathematically fixed. So if my polar axis is set 100% accurately — correct elevation angle, correct declination offset, perfectly vertical pole, exactly true south — then on a non-motorised manual setup I should be able to rotate left or right along the polar axis and every satellite from 4°W all the way to 154°E should fall perfectly on that same arc without needing any separate manual elevation or azimuth correction at the far ends. Is this correct?


And regarding USALS — my understanding is that when USALS corrects for small polar mount errors, it does NOT adjust elevation and azimuth separately as two independent corrections. Instead it simply moves the motor slightly left or right along the polar axis, and because of the polar mount geometry that single movement automatically corrects both azimuth and elevation together simultaneously. So elevation and azimuth are never truly independent on a polar mount they are always coupled through the polar axis rotation. Is this also correct?

The reason I ask is that for my manual non-motorised setup, if the above is true then I have nothing to worry about at the far ends of my arc I just rotate by hand until signal peaks and the geometry takes care of everything else automatically.


My setup details: 1.8m Prodelin dish, Ku band, main arc 4°W to 90°E with occasional tracking to 154°E horizon limit.

Thanks again!

 

[SEOShamsher]

also do LNB skew auto adjusted by polar mount rotation movements or need skew tweaking a bit?

 

[a33]

Basically you seem to be correct in your assumptions. But the initial setting is not just setting axis elevation and dish declination offset aiming at perfect south, but also the finetuning at the extremes. So it takes a while.

As @deeptho wrote: use "modified angles" for the initial setting! Hopefully, that would minimize the finetuning at the extremes.
For your LAT, I would use modified axis elevation 59.13-0.59=58.54 degrees, and modified dish declination offset angle 5.09-0.59=4.50, while aiming at perfect south. (Correction angle 0.59 is the max I would use for your LAT; it could also be taken about a tenth of a degree less (0.49) or so.)

Your setup should be aimed at true south. So before finding the azimuth for 75E, rotate the dish around the axis about 0.85 degree from true south. from the aligned axis and dish.

LNB skew would indeed not need adjustments.

Finetuning procedure is written on the internet (first correct the symmetry around the due south setting, then correct the elevation/declination combination).

Greetz,
A33

Edited, two corrections

 

[a33]

By the way
How did you find/calculate this angle:

Second axis — declination offset → 6.7°

?

I cannot reproduce how to get to that outcome...

Greetz,
A33

 

[SEOShamsher]

By the way
How did you find/calculate this angle:

?

I cannot reproduce how to get to that outcome...

Greetz,
A33

I did use AI but when actually starting will use online formulas and calculators as AI do make mistakes my bad

 

[SEOShamsher]

By the way
How did you find/calculate this angle:

?

I cannot reproduce how to get to that outcome...

Greetz,
A33

is it correct now??

 

[Channel Hopper]

Hi everyone,


I am in the process of converting my existing fixed dish mount into a non-motorised polar mount. I am getting it fabricated by a local welder with my own assistance.I am handling all the accuracy, calculations and angles myself while the welder handles the metalwork.


My location:Latitude: 30.86568° NLongitude: 75.84964° E(Ludhiana, Punjab, India)


Target arc: 4°W to 154°E (4 W at 0° elevation and 154 at 1.5° elevation)


The whole idea of this build is that once the polar axis is set correctly, I only need to rotate the dish left or right on a single axis to point at any satellite across the entire arc.no touching elevation, no touching azimuth ever again. Simple and effective.


My calculated settings:


True south → 178.1° on magnetic compass (corrected for magnetic declination = true 180°)First axis — polar axis tilt → 30.87° above horizon (equal to my site latitude)Second axis — declination offset → 6.7° below polar axis toward equatorCentre reference satellite → 75°E (compass 179.8° — almost perfect true south from my longitude)


I am confident in my calculations. My main concern is real-world accuracy after accurate fabrication and whether small errors compound at the far ends of such a wide arc.

---

My questions for experienced members:

1. Is my understanding correct — that after setting these two angles once during fabrication, I simply rotate the dish left or right on the polar axis to reach any satellite from 4°W all the way to 154°E with zero other adjustment?
2. Is there any natural geometric error that builds up at extreme arc edges (4°W and 154°E) even with a perfectly set polar axis — meaning a small elevation tweak may still be needed at the limits regardless of how accurate the build is?
3. Do professional factory-made polar mounts perform significantly better than a careful DIY fabricated one, or does it all come down to mechanical build precision and correct angles?
4. Do even professional installers find that wide arcs like mine need minor tweaking at the far east and far west limits, or does a correctly aligned polar axis track perfectly end to end?
5. My biggest concern — if after installation I discover a small pointing error at 154°E or 4°W and physically adjust the dish tilt to compensate, will that destroy my centre calibration for satellites near 75°E? Is there any way to correct edge errors without disturbing the centre?
6. Any tips for getting accurate angles during the welding fabrication process — tools, methods, or tricks to ensure the polar axis and declination offset are welded at exactly the right angles?

Thanks to anyone with hands-on experience with wide arc polar mounts or DIY fabrication. Really appreciate any guidance before I commit to welding!

I did similar with the first large dish I had af this property ( a 3.1m Patriot). welding the declination angle into the central canister sitting infront of the AJAK gearbox.

I found that no matter how stable the ground post was (having ensured the post was absolutely vertical, then bracing in two directions just under the motor), the weight of the dish would impact on the elevation at different parts of the arc.

Fortunately I had included an elevation motor into the installation for inclined orbit satellites and this served as a correction for the involuntary errors of the dish caused by its weight, along with the wear and tear on bearings and gearbox tolerances over the next five years.

 

[SEOShamsher]

I'm going to fit this at 4th floor terrace almost 40+ ft height. So this can help for stable pole. I've 5inch RCC slab very strong to hold this.

Pole dia is 101 mm and 10kg length is 4ft.

My plan is to build rcc block of 45cmx60cmx60cm and insert pole during casting along with two cross steel rodes weldeded into pole bottom for locking the pole.

probably pyramid type so dish bottom rim dont touch pole base foundation. like below. Her ein India most of time people do build pole base like this.

 

[a33]

is it correct now??View attachment 168583

Well, I would say no.
The elevation angle given is the satellite elevation angle for due south, not the axis elevation angle (neither the traditional axis elevation angle, nor the modified axis elevation angle).
The declination offset angle given is the "traditional angle, so not a (better!) modified declination offset angle.

So, why wouldn't you use the modified angles that I already provided for your LAT?

Greetz,
A33

 

[Channel Hopper]

I'm going to fit this at 4th floor terrace almost 40+ ft height. So this can help for stable pole. I've 5inch RCC slab very strong to hold this.

Pole dia is 101 mm and 10kg length is 4ft.

My plan is to build rcc block of 45cmx60cmx60cm and insert pole during casting along with two cross steel rodes weldeded into pole bottom for locking the pole.

probably pyramid type so dish bottom rim dont touch pole base foundation. like below. Her ein India most of time people do build pole base like this.


View attachment 168584

You will still need a motor - somewhere - for correction.

 

[SEOShamsher]

Well, I would say no.
The elevation angle given is the satellite elevation angle for due south, not the axis elevation angle (neither the traditional axis elevation angle, nor the modified axis elevation angle).
The declination offset angle given is the "traditional angle, so not a (better!) modified declination offset angle.

So, why wouldn't you use the modified angles that I already provided for your LAT?

Greetz,
A33

I got it now. good to go!

I got confused it with satellite elevation earlier.

 

[SEOShamsher]

You will still need a motor - somewhere - for correction.

for the moment, I'll use it without motor as I want to make sat hunting more easy. Down the lane, going to use motor.

 

[SEOShamsher]

I'll do multi LNB setup once I'm done exploring the sky for few weeks.

Final destination 13 E hotbird as center satellite. 4, 7, 9, 10, 16 , 26, as side LNBs.

 

[Channel Hopper]

LNB skew would indeed not need adjustments.

Finetuning procedure is written on the internet (first correct the symmetry around the due south setting, then correct the elevation/declination combination).

Greetz,
A33

Edited, two corrections

Some satellites are 'skewed' to a different angle from the usual selection.

I would factor something in when looking for signals at the footprint limits

 

[SEOShamsher]

Some satellites are 'skewed' to a different angle from the usual selection.

I would factor something in when looking for signals at the footprint limits

Do you mean online skew calculators can be also wrong?

 

[deeptho]

Do you mean online skew calculators can be also wrong?

The satellite operator chooses the skew angle, which means that it can be different for different satellites, but I also read somewhere
tha a few years ago some satellites that had an unusual skew setting went back to the standard one.

About your question on tracking the arc: I think a lot has been answered by others, but to repeat and confirm:

• No polarmount can 100% accurately track the arc, but the errors can be small; in addition the dish weight can stress the pole differently at the extremes causing slight bending
• usals is jus a method to compute the rotation azimuth angle for a given satellite position. An usals motor only performs that rotation; nothing else
• the "modified angles" only refer to declination and elevation. Only for a satellite exactly due south, elevation plus declination equals the angle of the satellite above the horizon. So that means for such a sat, only the sum matters. For satellites not due south a more complex equation applies and this is why declination and elevation must be correct each on their own.

 

[a33]

Do you mean online skew calculators can be also wrong?

The Astra satellites (19E, 23E and 28E) have a preskew of 7.5 degrees.
The Eutelsat satellites (13E and others) have a preskew of 3.535 degrees.

In a motorized setup, it is customary to discard this preskew, and assume skew = 0 towards due south.
While rotating the dish, the skew of you setup rotates with it, so that the endresult skew again about matches the skew of the chosen satellite.

However... I believe for the region of Australia, there are one or more satellite positions that have/had a preskew of 45 degrees. In that case, you would indeed have to rotate the LNB.

Calculators often don't mention if their reported skew takes the preskew into account, or not. That is a nuisance....

Greetz,
A33

 

[a33]

the "modified angles" only refer to declination and elevation. Only for a satellite exactly due south, elevation plus declination equals the angle of the satellite above the horizon. So that means for such a sat, only the sum matters. For satellites not due south a more complex equation applies and this is why declination and elevation must be correct each on their own.

The weird thing is: The charts with modified motor angles, that I found on the internet, all use modified angles that are based on the declination fit for invisible satellites (below the horizon); using what I call the 0-90 degrees fit, or the 0-180 degrees fit.
So that even when you are at latitude 80, the forward axis tilt in the charts is bigger than 0.20, though for the small range of visible satellites the needed forward axis tilt actually is only maximally 0.03!
So most/all charts on the internet overcompensate. @B.J. alias @wejones (great advocate for the modified angles) hinted to that, already.
I made new calculations for a 0-horizon fit chart (I used that chart in the post above). I guess that approach still overcompensates a little bit, for the visible part of the arc, but I assume it is already much better than the other charts. Though I have never further calculated on that for the inbetween parts of the visible arc.

Thankfully all is about just tenths of a degree, so being a bit off is not a very big problem.

Greetz,
A33