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).
There is something wrong: when I try to log on to your site, I get a warning about "security certificate" and a recommendation NOT to proceed, which I ignore.
This may put off more-timid souls!
What is the problem?
Eric I no longer use the motor on my dish to get the other satellites but 4 separate quad LNBs fixed to a bracket on my dish and cabled to diseqc switches. Both my Passions and my Panasonic boxes have DiSEqC 1.0 software which allows switching between the various satellite positions without moving the dish. The Panasonic box doesn't support Diseqc 1.2 which the Passions do support and which allows them to operate the motor. It was the absence of Diseqc 1.2 in the Panasonic firmware which forced me to invest in the bracket and the extra 3 LNBs but as I said in my last reply it is actually better in that you can record from different satellite positions at the same time which you couldn't with the motor. The motor with a single quad LNB can only point at one position at a time whereas using Diseqc switches means you have an LNB dedicated to each satellite position and the receivers switch between the LNBs electronically. 3Sat is a German language programme broadcast at 19.2? East. At the time I bought my Panasonic box I wanted to be able to burn Blu Rays and as far as I know Panasonic is the only company providing recorders with this function. Alas Panasonic UK had stopped marketing Satellite equipment by then so I had no choice but to buy it from Germany. It has a slight disadvantage in that its not a Freesat machine so doesn't support the Freesat EPG but only Now & Next on UK broadcasts. The EPG works fine on German and other language broadcasts and you can record UK programmes with the timer. Since buying the Panasonic I have invested in a couple of media servers and so if I want to archive a video now I just copy it to the media server. An advantage of it not being a Freesat box is that it does allow me to stream HD video. I have a very similar Panasonic Blu Ray Freeview recorder which only allows me to stream SD video so I suspect that a Freesat recorder would be similarly restricted. I don't have any experience of other satellite receivers which allow USB recording but there are several on the market. Until quite recently I would have advised use of a recorder with a built in hard drive like the Panasonic rather than an external USB drive as I have always found the Passion+ a bit flaky but both my Panasonic recorders have started playing up lately with HDMI blackouts followed by reboots which leave me with 2-3 minute gaps in my recordings. Not great when you are recording a Mozart symphony! I've never had my Passion+ render a drive unreadable although it frequently can't read the drive. I used to follow a tip I read once and plug the drive into my laptop and delete a recording I no longer require, reboot the Passion+ and plug in the USB drive again and it often seems to work again. I also used to record a few short clips to give me something to delete.
Neil, I'm puzzled by your explanations (thanks); if a dish is properly aligned to a given satellite, the LNB is held at the focal point of the dish. If your switching system changes to another LNB and moves it so that it is at the focal point, the dish will still be pointing at the original satellite. Does your system rely on good strong signals from the other satellites; strong enough to be picked up by a wrongly aligned dish?
Hi Eric My 1.2 metre dish is pointing at 23.5 degrees East where the Czech programmes reside (these being the weakest I watch). Clamped on the arm is a bracket which can take another 3 LNBs which are positioned individually to receive signals from satellites located to the left and the right of 23.5 degrees East. The size of the dish more than compensates for any discrepancy in the shape of the elipse as seen by the other LNBs and I get excellent signals on both UK broadcasts at 28.2 and German broadcasts at 19.2 and very good results on Hotbird at 13 degrees East. Its the position of the LNB relative to the satellite which is critical rather than how close it is to the focal point of the dish. Its not just at the focal point that you get a strong signal but on an arc either side of it. Neil
When planning to install a satellitedish, there are certain regulations that need to be considered. In general a dish of up to 1m in any dimension does not need planning permission unless it is in a conservation area or the building is listed. A 1.2m dish definitely needs planning permission, see Planning Portal - Satellite,TV and Radio Antenna for full details of what is and is not permitted.
Mike P I have never looked at that web site before and on a quick look today I couldn't find any reference to the maximum size for satellite dishes. However when I had my 1.2 meter dish installed some years ago I did look at my local authorities (Redbridge) web site where it said that planning permission was not required for a satellite dish and additionally there was no mention of maximum size. I think it did mention listed buildings and conservation areas but as I live in neither I didn't concern myself further. I've had people visit from the planning dept. in connection with a neighbours planning application more recently and no comment was made and I've not had any complaints despite the dish being inline with the front of the house, on a big bracket with the motor and quite low down ( I can reach it with a tall step ladder) so its not been an issue for me.
The site states "if you are installing a single antenna, it is not more than 100 centimetres in any linear dimension (not including any projecting feed element, reinforcing rim, mounting and brackets);". That is in the secrtion dealing with houses up to 15m high, which covers most 2 storey houses in the UK. It's the second bullet point. That requirement has been in force for many years, certainly since before the turn of the century.
I assume that because your enquiries with your local council at the time of installation led you to believe that permission was not needed, then it is possible that a different member of staff could interpret that as being in need of retrospective consent.
Mike P Your'e certainly correct. I was looking for the word "max" which of course isn't there. I also note on the Redbridge site that it links through to the Planning Portal now which I don't recall it doing in 2007 when I had the larger dish fitted. I'll just have to hope that nobody notices.