Elevation problem - Stockholm Area

[Stockholm_Calling]

Hi

I’ve recently purchased a secondhand Channel Master 1.2m dish with polar mount and I need help in establishing the correct elevation. The polar mount isn’t a CM, but some other make/brand and there’s very little I can change on the polar mount apart from azimuth and elevation (see attachments). The scale on the polar mount ranges from 50 to 70 degrees and to be quite honest the point is useless.

The main satellite I’m interested in is Astra2D though I’ve tried setting up the dish towards Thor 2/3 1W that has an elevation requirement of 20°, but again no luck!

I know that CM has a reflector offset of 22.6°, so I’m assuming that the dish needs to be down tilted by some 2-5°…is this correct?

Thanks in advance,
Anthony

Based on my location (Stockholm) the set up should be as following:
Latitude: 59.4°
Longitude: 17.9°

Satellite orbit: 28.2E Astra 2A, 2B, 2C, 2D
Elevation: 22.0°
Azimuth (true): 168.0°
Azimuth (magn.): 164.1°
Polarisation tilt (deg): -6.04 (though for Astra satellites + 7 ) = 1.04°

Polar mount main axis angle (deg): 60°
Polar mount dish offset tilt (deg); 7.42

 

[Stockholm_Calling]

Attachments added.

Anthony

 

[Robbo]

Errm, The mount doesn't look right for the job, as you have no declination adjustment possibilities.

The swivelling bit, should be at an angle of 30.6 degrees from vertical for your location.
(90-Latitude).

The dish face itself, very close to vertical when at the apex of the arc.

( Because the theoretical fixed dish elevation figure for a satellite at your due south is 22.64 degrees)

 

[guest poster]

You could give yourself declination adjustment using longer bolts where the polar mount is bolted on to the back of the dish and get you polar angle right and move the angle of the dish (on the longer bolts) until you have position where it matches the dish offset and use spacers (washers. nuts. cut small bore pipe) in between the back plate and the polar mount to get the angle..

EDIT... looking at the angle ... just replace bottom two bolts with longer ones and loosen the top two until you get the angle.... also possibly better to use slotted spacers so that you can adjust without undoing the bolts completely.

EDIt 2... actually... if there is enough room ... using 4 nuts on the long bolts (in between the polar mount plate and the dish back plate) could give you the fine adjustment and allow for it to be tightened up ..... that would work well...

 

[Channel Hopper]

Errm, The mount doesn't look right for the job, as you have no declination adjustment possibilities.

Hammering the top spar until it bends will give some adjustment.

But I would be inclined (sic) to cut it in half, overlap the two halves, and bolt together at the right point when the arc is correct on the mount.

 

[Stockholm_Calling]

Hi Robbo,

When you say "The swivelling bit, should be at an angle of 30.6 degrees from vertical for your location.
(90-Latitude)." do you mean the angle as depicted in the attached photo (A little difficult to see from the last photo)? If so, then it is approximately 30 degrees when the dish is vertical, i.e. 90 degrees.

Pedro's idea was interesting... what sort of figures are we talking about with regards to the declination angle. Is it 7 degrees or so, i.e. the Polar mount dish offset tilt?

Anthony

 

[Robbo]

Hi Robbo,

When you say "The swivelling bit, should be at an angle of 30.6 degrees from vertical for your location.
(90-Latitude)." do you mean the angle as depicted in the attached photo (A little difficult to see from the last photo)? If so, then it is approximately 30 degrees when the dish is vertical, i.e. 90 degrees.

Yes, your new picture is much better. Yes the angle you have labelled as 30 degrees should be 30.6 degrees. As close as you can get it to that.

 

[Stockholm_Calling]

Ok...if the polar mount angle is fine, then what I need to do is to push the bottom of the dish out (using Pedro's tip) to introduce a declination angle. And then set the elevation angle to 22 degrees...correct?!

Anthony

 

[Robbo]

The declination angle for your lat is 7.96 by my quick calculations.

Your dish offset angle is 22.6 degrees.(you said)

Thus the angle between the axis of rotation (the swivelly bit) and the plate on the back of the dish will be 22.6 +7.96=30.566 degrees.

The dish offset is added as you need to add to the declination, the dish offset angle, to account for the fact the the dish is pointing up the air, when the back plate is vertical.

You would set the dish as above. Then send to your nearest due south satellite (19.2), then tweak the dish, and swivel the polar mount around the main pole for max signal.

To move the dish to 19.E, you would work out the difference between your longitude and the satellite's polar position.

Once that is all done, you should be tracking the arc fairly well, ready to move the dish around to 28E.

Adjustment should only be done at the apex of the arc.