Why top of arc?

[Basmati]

Hello,

I'm trying to install a 10' motorised dish. I'm very new to this. I read some setup instructions regarding finding the arc and they invariably telling to find the top of the arc first. Why would any other point not good enough if the correct elevation, declination, skew angles are observed?

Please shed some lights on this point for me. Thank you.

Cheers,
Basmati

 

[nistleboy]

If you are on top of the arc the rest of the sats should fall in if your set up is ok. In the uk you could find 28 e with an out of line dish. It's just easier when you find top of the arc.

 

[Basmati]

You mean if I take a point on the side of the arc, the dish won't move up along the arc even if all the parameters for the initial point is correct?

 

[rolfw]

It is a lot easier as nistleboy says if the satellite you are looking for is at the top of the arc, even more so when you are trying to align a large dish.

You have a satellite right at the top of your arc NSS 12 at 57degrees East with both C Band and Ku band channels, The East African Beam Ku band channels should come in strongly with your proposed dish.

 

[Basmati]

rolfw, you are right, NSS12 is right at the top of my arc but Arabsat 5A which is 30.5 East has stronger signal. Does NSS 12 still my best bet or should I go with the Arabsat 5A? Thanks.

 

[Robbo]

It doesn't have to be done on the strongest satellite, you just need to be able to receive it. Alignment can be more precise doing it on a weaker signal anyway. Also the top of the arc is relatively flat, but is steeper at the sides, so easier to adjust.

Also since it is a polar mount you won't be able to use USALS, so to align on a sat that is not on your due south, the chance of an error when offsetting the motor position to allow for the difference between your longitude and the satellite's longitude is greater.

 

[Basmati]

It doesn't have to be done on the strongest satellite, you just need to be able to receive it. Alignment can be more precise doing it on a weaker signal anyway. Also the top of the arc is relatively flat, but is steeper at the sides, so easier to adjust.

This is clear now!

Also since it is a polar mount you won't be able to use USALS, so to align on a sat that is not on your due south, the chance of an error when offsetting the motor position to allow for the difference between your longitude and the satellite's longitude is greater.

If I'll be using an actuator arm, will the dish move off track if the starting point is not at the top?

 

[Robbo]

It would be off track yes, if it was not setup properly, but not necessarily. It would be more difficult to achieve is the point.

When making the inititial alignment with a motorised dish using a satellite that is exactly at your due NORTH location, the polar mount can be set to centre and alignment carried out. Assuming that all other things are correct, the dish would then follow the arc.

However, when aligning to a satellite that is NOT at your due north, the polar mount has to turned either east or west (depending which way the satellite is with respect to your due north sat), before commencing alignment. However turning the motor to that satellite can be innacurate. Getting it wrong on such a large dish would mean the whole arc just crossing at that point only.

Correction to my previous post, I note that you are in the southern hemisphere, so it should be due north rather than due south.

 

[Basmati]

Thanks Rocco for these explanations. Indeed I am in the southern hemisphere. Like roflw mentioned, my best bet would be to aim at NSS 12 for the alignment purposes. Thanks again.

 

[Analoguesat]

A 10' dish will be a b@$t@rd to set up - it really needs someone who knows what they are doing with big dishes and has professional grade tools..

 

[Basmati]

A 10' dish will be a b@$t@rd to set up - it really needs someone who knows what they are doing with big dishes and has professional grade tools..

I think if I can measure the angles correctly I should be ok. For example, if I take the NSS12 satellite as my due north and adjust the dish with the correct elevation, declination and lnb skew, I should be on the arc, right?

 

[Analoguesat]

Its not as simple as that - big dishes

1) are very heavy

2) are awkward to work on

3) have very very narrow acceptance angles which makes them tricky to set up.

I wish you luck but dont be surprised if you have trouble.

 

[Basmati]

Thanks for the caveat Analoguesat. I'll keep that in mind!

 

[Analoguesat]

Oh - I see from your profile you have a mesh dish - is this a c-band dish (mesh) or a Ku band dish (perforated)

A small but crucial difference.

 

[Basmati]

It's a c band mesh dish! Why crucial?

 

[Analoguesat]

If yoiu are after Ku band it wont work very well. Or are you just motorising for the few C-band satellites out there?

If its c-band it will be simpler to set up due to the lower frequencies use.d

 

[Basmati]

I'm after the C-band only for the moment until I acquire more expertise to tackle the ku band

 

[Analoguesat]

Well as I said that should be a bit easier to set up, and will give you useful experience for the trickier Ku stuff later.

Please post a photo when you have the dish up - we always like to see what our members have in their back gardens

 

[Basmati]

Ok I'll do that after I install the actuator.

 

[Basmati]

It is a lot easier as nistleboy says if the satellite you are looking for is at the top of the arc, even more so when you are trying to align a large dish.

You have a satellite right at the top of your arc NSS 12 at 57degrees East with both C Band and Ku band channels, The East African Beam Ku band channels should come in strongly with your proposed dish.

NSS 12 is 359.13° my True North. Can I take it literally as my true north and get a perfect arc? Thanks.