Farmsky

Dear fellow,

I'm not sure where you have 'learnt' your extremely limited and always misleading information on satellites ....... but you are ...... simply full of it!

The 'Hills Gemini Satellite dish alignment settings' guide posted earlier by After Hour Z is spot on; as you would expect from a major industry supplier like Hills.

As I have explained elsewhere the Optus series satellites are tilted on their flight axis wrt other satellites. The actual tilt or variation from a standard skew is not 40 degrees. Rather it is 45 degrees.

Stare up at the sky and imagine the Clarke Belt spreading in an arc from east to west. Imagine a point at the apex of the arc ie due north. Now a satellite here would normally be vertical. If it is an Optus satellite it is tilted 45 degrees to the left. That's what the Optus 'mystery' is about. Of course this put's it midway between vertical and horizontal if you are aligned for a 'normal skew' satellite.

So the trick when using any dish pointing software is to simply 'add on' the special Optus skew (45 degrees).

The correct skew setting for Sydney OPTUS C1 is +38 degrees which is where I suspect poor old beerforlife's 40 'Sydney centric' view comes from.

But what does this mean?

Looking into the dish (Sydney), the lnb is rotated 38 degrees clockwise from vertical. ie starting with the cable exit point down (6 o'clock). 38 degrees is a bit past 7 0'clock (30 degrees) which is the common reference we generally talk about for C1 in Sydney. The lnb's manufacture's tolerance may vary this a bit, even between like lnb's.

The other main Optus birds will have slightly different skews in Sydney. e.g

Optus D2 (152 E) Skew = 44 deg
Optus C1 (156 E) Skew = 38 deg
Optus D1 (160 E) Skew = 32 deg

..... But all still pretty close to 7 o'clock

The following explanation will completely lose beerfor life; but bear with me.

An excellent dish pointing skew calculator is available at satlex. Have a look at this site and plug in various satellites and locations. You will notice how the skew changes with satellite and location. If you can get your head around it; this site and the nice graphics will also explain why the skew varies with satellite and location. It should also give you an insight as to why the skew is 'automatically adjusted' on a polar mount as you 'roll' around the Clarke Belt.

However the Satlex site (and none of the web calculators that I know of apart from the published calculators like Hills), take into account the different Optus skew.

So this is how you calculate it using a standard dish pointer.

Satlex indicates +7.1 deg for Optus C1 in Sydney. So 7 - 45 = -38 degrees (or a bit past 7 0'clock). Which by the way matches the Hills chart.

Note: +/- skew depends on how you look at the skew rotation. There does not appear to be a standard nomenclature here.

So what about Perth?

Satlex indicates +46 for Optus C1 in Perth. So 46 - 45 = 1 degree (or 6 o'clock). Which again perfectly matches the Hills chart.

And if you want it from the horse's mouth, here is Optus's neat little skew chart for Optus C1 from the 'Optus Satellite Network Designers Guide'.



And they provide them for all their orbital slots.