Today’s technical post is on the best practices of satellite dish alignment and is one of the most important stages of IRS commissioning. Let’s take a look at the selection of satellite dishes available there’s a wide choice, but there are some general rules to follow.
Before selecting your satellite dish it’s worthwhile checking line of sight, this can be done in a variety of ways, a quick check before setting off in the van with online services like DishPointer will show a top down visual and a rough line of sight indication this can show any serious obstacles (adjacent tower blocks for example), but this doesn’t account for recent building developments so a site survey is an absolute requirement. The same DishPointer web site provides satellite look angles. Azimuth Magn (where you can use a magnetic compass to acquire the general direction) and Elevation (you’ll need an inclinometer). Most mobile phones have these features or can be downloaded as apps.
Pointing tools on mobile phones can be a useful aid, but should only be used as a rough guide and never as an alignment tool. DishPointer also has an app that features a visual guide using augmented reality. As a general rule of thumb if your site has clear line of sight to the southern horizon you’re off to a good start.
You might be tempted to use a domestic satellite dish for your IRS system but, there will be insufficient gain from a Zone 1 or Zone 2 satellite dish and using either of these will result in call backs due to poor system performance, the right size dish is essential.
For most UK installation sites an 88cm dish would be ideal. However, sites towards the far north and further west would benefit from a 110cm dish. Astra publishes their satellite EIRP figures and this short table illustrates the typical satellite dish sizes (assuming a Universal LNB with a 0.7dB noise figure).
EIRP (dBw) Dish Diameter (cm)
54 45 (Zone 1 Domestic Dish for use in the South)
50 60 (Zone 2 Domestic Dish for use in the North)
45 88cm (IRS Dish for use in the South)
42 110cm (IRS Dish for use in the North)
Now that we have an appropriately sized satellite dish and a clear line of sight the next steps are alignment. For this you will need a professional satellite meter/spectrum analyser that has the ability to clearly identify Astra 2 at 28.2° east, the right tools and patience. Time spent on the precision alignment and neat installation will sustain excellent service for years to come.
We’ll be covering the alignment steps in the next technical post.