Hello,
I want to set up the correct angles for my motorised cband dish.
I have been using the website dishpointer.com and it tells me to point the dish to true north, elevation angle = 57.2 degrees and declination angle = 4.7 degrees.
But i'm not sure where to measure the elevation angle and the declination angle for my dish.
Your friend Cunnamulla.
Thank you for your response, but I have read this tutorial many times now and am struggling to understand where I should measure the angles I got from dishpointer. You can see this on page 12 of the tutorial
Where do I measure the 57.2 elevation angle and where do I measure the 4.7 declination angle?
At true north, does my dish have a total elevation of 61.9 degrees or a total elevation of 57.2 degrees?
Although I don't have a motorised setup (maybe one day), I too would like to know the difference between elevation and declination.
It seems a bit weird to me as I have two telescopes; one with an Az-El mount (Azimuth-Elevation), and the other with an equatorial mount (RA & Declination).
A motorised dish should be similar to a telescope's equatorial mount but I still can't quite picture why a dish needs the third adjustment.
It'll probably be obvious once someone explains it, but I just can't get it from that tutorial.
Declination Angle Chart
or
(to ,,)
Explanation of Declination
Declination angle keeps satellite antenna from
aiming into deep space and changes value with
latitude in accordance to earth's curvature. Early astronomers developed the
polar mount to track stars. For deep
space tracking, i.e. star observation,
the elevation setting of the polar mount
is equal to the latitude of the site
location. However, geostationary
satellites are much closer to earth than are celestrial objects and their observation requires a slight tilting 'downwards' from deep space
observation settings to see the geostationary satellite arc. This adjustment of (to) the polar mount, the tilting downwards, is the declination adjustment of the polar mount and its amount is the declination offset angle (not to be confused with the declination angle which is the sum of the declination offset angle and the polar axis zenith elevation angle).
The declination angle is determined by the formula below where 22300 is the distance from the surface of the earth to the satellite belt and 3964 is the radius of the earth (both in km.). (In error, should be Miles.)
In summary, the declination angle lowers the satellite antenna from looking into deep space to look at the arc of geostationary satellites. However, upon practice, it has been discovered that using the latitude as the elevation angle, (), the satellites at the top of the arc, in a tracking mount system, were in perfect alignment with the satellite dish, i.e. were tracked perfectly by the polar mount, whereas the satellites at the lower ends of the arc where not tracking correctly. Conversely, if the satellites at the ends of the arc, on the horizon, were tracking correctly then the central satellites, at the top of the arc would be slightly off target. This effect is caused by the slight deviation from the true north/south line, caused by the act of the tilting of the dish, as the dish moves to view satellites lower on the arc, i.e. closer to the horizon. With this in mind, it was formulated the elevation/declination angles of the modified polar mount () whose application has no effect on seeing satellites at the top of the arc but has the effect of better tracking on the sides and low end of the arc. This effect is accomplished by slightly increasing the elevation angle and accordingly slightly decreasing the declination angle by the same amount. Use elevation/declination settings from the (second chart below) when installing and adjusting your polar mount tracking system - compare the values of the two charts below to see the difference in elevation and declination angles. Note: Elevation and declination angles are always measured and applied when the dish is at its zenith, i.e. highest point in the arc, when the dish axis is aligned along the true north-south line. (.) Declination angle for normal mounts may be found by using the following equation:
ARCTAN((3964*SIN(L)/(22300+3964(1-COS(L)))))
Where 'L' is your site latitude.
NOTE: This formula does not yield modified polar mount declination values but yields the values in the chart immediately below. Declination Angle Chart
NOTE: This table is for traditional polar mount adjustment where elevation angle=latitude;
for modified polar mount declination values see below.
Modified Polar Mount Tracking Angles
NOTE: Elevation Angle is the angle measured on (at) the pivot axis of the mount. To get the Total Declination Angle setting as measured on (at) the back of the dish ring (dish mount), add the Declination Offset Angle to the Elevation Angle. In summary, the difference between the Total Declination Angle and the Elevation Angle is the Declination Offset Angle. Elevation and Declination Angles are always measured and applied when the dish is at its zenith, i.e. highest point in the arc, when the dish axis is aligned along the true north-south line.
Last edited by beer4life; 07-08-09 at 12:22 PM.
Andy Chee (06-08-09)
beer4life thank you for helping here.
I think I understand everything now. Can you please check my maths for me so that I know i'm going to get this right.
According to dishpointer.com using my address:
Elevation angle = 57.2
Declination offset angle = 4.7
Therefore at zenith the total azimuth elevation is 61.9 degrees?
G'Day,
I believe that would be correct. However I've only set up H to H Dishes, not a C Band. So if there is any one that has more experience, please feel free to correct me.
It would seem that I have to correct myself. See next post.
Kindest Regards, " The Druid "......
Last edited by beer4life; 06-08-09 at 07:03 PM.
On second thoughts, we are becoming confused here.
Use the chart near the end of that tutorial where elevation is approximately the reciprocal of the Latitude and total declination angle is given as elevation - declination.
There is detailed explanation where to set the various angles.
I'm afraid I am at a loss to explain it better.
Last edited by beer4life; 07-08-09 at 09:53 AM.
I'll be installing my 2.3m C band motorized dish in the next few weeks and I have been researching this topic. The way I understand is that the elevation angle is equal to 90deg - Latitude.
My place is located in Latitude 33.77 South so my elevation angle would be 90-33.77 = 56.3 degrees if I will be tracking the deep space or a star at another galaxy. Now to track a closer satellite I have to dip the dish a bit by the amount of the declination offset 4.79 degree. Then my total angle of the polar mount is therefore 56.3-4.79 = 51.51degree from the horizon or 38.49degree from vertical (plumb pole of the dish).
There is a bit of confusion in the above postings since the angles quoted does not reference the angles being measured from.
I may be wrong but this is what I understand from what I 've researched so far.
Attached is a sketch I did to explain how I understand thing. Remember I could be wrong so please correct me if I am wrong.
And hopefully someone can confirm my understanding of the difference between the traditional polar mount and a modified polar mount.
In the traditional polar mount, the declination axis pivots from the same point as the elevation axis.
In the modified polar mount, the declination axis pivot point is further up the elevation axis.
Yes?
Yes, well done.
That puts it in a nutshell what I said in the previous post.
Two manuals for H to H motors (30 and 40 Degree cranks.) give the Elevation as the reciprocal of the latitude, as it should be.
If you look at the post of that article, you will also see that I have also corrected the error of Kms and Miles for the Clarke Belt.
It's a bloody nuisance as I've been searching everywhere for a correct version of the facts.
No wonder people have difficulty grasping how to set up and adjust with such mis-information.
Kindest Regards, " The Druid ".
Sorry Cobber, I missed your post. This is the reason:-
This should help with final tweaking:-This effect is caused by the slight deviation from the true north/south line, caused by the act of the tilting of the dish, as the dish moves to view satellites lower on the arc, i.e. closer to the horizon. With this in mind, it was formulated the elevation/declination angles of the modified polar mount () whose application has no effect on seeing satellites at the top of the arc but has the effect of better tracking on the sides and low end of the arc. This effect is accomplished by slightly increasing the elevation angle and accordingly slightly decreasing the declination angle by the same amount. Use elevation/declination settings from the (second chart below) when installing and adjusting your polar mount tracking system
Last edited by beer4life; 07-08-09 at 04:12 PM.
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