Site settings

Freesat reception - all about dishes

Satellite reception has both advantages and disadvantages compared with terrestrial (aerial) reception.

^{Published on 10th September 2006 at 12:42 by Brian Butterworth on UK Free TV}

Satellite reception has both advantages and disadvantages compare with terrestrial (aerial) reception.

By using much higher frequencies (gigahertz, compared to terrestrial televisions megahertz) more transmission channels called transponders (the satellite equivalent of multiplexes) can be provided. For example, there are only six Freeview multiplexes, but Sky or Freesat users can access two hundred satellite transponders.

Aside from exceptional weather conditions (very heavy rain for example) digital satellite provides stable pictures and audio. Where Freeview transmitters are no more than 732 metres above sea level, the geostationary satellites used for television are 35,800,000 metres above the equator so reception is possible even where buildings, trees and hills make terrestrial reception impossible.

The downside of the transmitters being 22,300 miles up in the air is that the signals are very, very weak - so standard TV aerial is of little use. When the signals are sent to the satellites, huge dish transmitters are used to uplink the signal to the satellite. These are tens of metres from side to side, and feature an emitter that generates the signal, which is first bounced of a mirror (called a reflector) and then off the surface of the parabolic dish.

There are many satellites in the sky over the equator. Often these are in clusters over a particular position, for example there are four used for UK television are at 28.2 degrees east. There is another cluster over the 19.2 degrees east positions that are used for German television.

To receive these very weak signals from the satellite, it is necessary to use a dish for reception too. By using a reflective dish, this concentrates the signals onto a small device called a LNB. This is held in front of the dish by a metal arm.

The size of dish for reception is typically much smaller; often 60cm to 100cm in diameter, but the exact size depends upon the transmitting satellite transponder. To keep the transmission power levels down to levels that can be powered by the satellite's solar panels, each beam is focused on a particular area of the Earth's surface. If you are trying to receive the signal at the centre of this zone, a small dish is required. At the outer edges, you may need a 5 metre dish. Maps of these zones are provided by the satellite companies, and are called satellite footprints.

When the dish is installed it must be aligned carefully as the signal is very weak. The installer needs to know the inclination and the azimuth from the ground location to the satellite. If you install yourself you will find that there are markings on the dish that are used to point the dish in the correct position. It is important that the view of the satellite will not be blocked, so must take into account leaves growing on trees and potential building works.

For many people the LNB will have a single cable connected to it, however if you have Sky+ or a multi-room installation the LNB package will actually contain four receivers a quad-LNB. Unlike terrestrial television where you can split the aerial cable to feed more than one Freeview box or television set, with satelite reception you cannot. So, a Sky+ box with two receivers (so you can watch one thing and record another) has two cables connecting the box to the dish.

The cable that connects the dish to the receiver must be satellite grade cable. Whilst this looks superficially like the cable used to connect and aerial to a television, a higher grade cable is required for satellite reception.

Here is an image of a co-axial cable. This sort of cable is used to connect any type of receiving aerial to the reception equipment.

RG6, PF100 and PH100 are all types of coax cable that are suitable for the very weak signals that are received by a satellite dish. (The power is the same as you would receive from a one-bar electric heater on the moon).

The conductor in the centre passes the signals received from the dish to the set-top box. This is made from steel in RG6 cable, and from copper in the RF100 and PH100 types. This makes RG6 less suitable in the UK where rain can damage the cable.

The shielding is responsible for keeping unwanted external interference from damaging the signal. In the cheaper cable this will be a foil wrap, in better specified cables this is a braid (or mesh) of copper wires. The sheild in the RF100 covers 58% of the cable.

The non-conducting layer between the shield and the conductor is called the dielectric. This can be either a solid (RG6), foam (RF100) or air-spaced (PH100) dielectric. This makes the cables progressively more flexible (ie bendy without damage).

Your comments: most recent posts are at the bottom

First comments Earlier comments ◊ Later comments Latest comments

Your comments are always welcome. Please use the form below to add your thoughts or questions to this page. We will get back to you as soon as we can.

NottsUK
Monday 1 December 2008 1:07PM

Briantist: Looking at your figures again I realise that 35,800,000 metres is 35,800 Kilometres.

347 posts

Briantist
Wednesday 3 December 2008 7:49AM

NottsUK: At least you didn't make the mistake I saw the other day on the BBC News site, where they had "kilograms of force" in a story - twice.

Want a clearer search or information about missing Freeview light channels?	1
22nd May 2013 retunes for Devon and Carmarthenshire	2
Apologies for UK Free down this morning	3
15th May 2013 retunes for Yorkshire coast and Dorset, Wiltshire, Isle Of Wight	4
Want to see where a point on a line of sight on a map? Click on UK Free TV!	5
Want to better understand the current TV faults? See the all new UK Free TV page	6
Want EVEN better ADVANCED aerial to Freeview transmitter terrain plots?	7
Want better aerial to Freeview transmitter terrain plots? Check out UK Free TV!	8
Brighton to be the fourth at800 test area from mid-May 2013	9

KMJ,Derby michael r: To record tv on a satellite PVR you nee	1
jb38 Chinta: Try disconnecting the box from the power supply	2
KMJ,Derby Pauline: It might be worth noting that Digital UK	3
michael r the satellite dish on our rented property has 2 pa	4
Kelly 13danycoed Bridgend Blackmill Cf35 6es (Cf35 6e	5
Chinta Hi all, for 2 days I have no tv as it gives me error	6
jb38 Matt: Apart from checking the cables out maybe you coul	7
Dave Lindsay Caroline Hewitt: The format for analogue (possi	8
Caroline Hewitt Hi just got a new freeview tv for the bedroo	9
Tads Since the retune at the beginning of May, I have lost m	10

Freeview reception predicton	1
What price for an aerial installation? \| Rigger's zone	2
What can I do when my Sky Digibox says 'No Signal' or 'Technical fault'?	3
All free-to-watch channels	4
Can I receive British Eurosport for free?	5
My Sky box has a "no signal message" - what do I do?	6
Can I stop paying Sky and use my satellite receiver to get Freeview ?	7
Winter Hill (Bolton, England) Full-Freeview transmitter	8
Sutton Coldfield (Birmingham, England) Full-Freeview transmitter	9

Can I stop paying Sky and use my satellite receiver to get Freeview ?	1
My Freeview box has no EPG, is blank on FIVE, ITV3, ITV4, ITV2+1, has no sound or the channel line up is wrong	2
What can I do when my Sky Digibox says 'No Signal' or 'Technical fault'?	3
Can I use my ex-contract sky digital satellite receiver to get Freeview channels?	4
Can I receive British Eurosport for free?	5
My Sky box has a "no signal message" - what do I do?	6
How do I change the RF output channel on a Sky Digibox?	7
My high gain aerial can't get all the Freeview channels I expected	8
How can I get Channel 5 on Sky in Ireland?	9
How can I watch Channel 4 and five on satellite if I have no card or a free-to-view card?	10