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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 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.
Bob H Tuesday 24 April 2012 6:31PM
Colin: Somewhere on your Freesatbox you should be able to see signal strength/quality, check to see what you are getting. If weak then your dish may have moved or not been installed and aligned correctly or your LNB ( the bit with wires comeing out) may need replacing. Is the connection to your Freesat Box good? I found one where the central wire was bent over and not going into the central hole.
We live just outside Paris use a satellitedish to watch BBC and ITV channels. Just realised we now need to switch to Astra 1N satellite for BBC. How do we get ITV channels please ? Any help would be much appreciated.
Heather Naslin: When the channels moved from the Astra 2D satellite to the Astra 1N satellite, they mostly stayed on the same frequencies. You shouldn't have needed to do anything.
ITV have been moving services around a bit, so if they've moved your preferred regional service somewhere else, you might need to retune. If you have a Skybox, it should have retuned automatically, but you might need to check that the viewing card is properly inserted. Freesat boxes are supposed to retune automatically as well, but some of them need to be powered off and on again before they retune. Others actually have to be told to retune.
Paul: If its the case that you want to install an additional Freesatbox (HD or otherwise) so that the second location can view different programmes from whatever is being viewed on the Samsung, then you have to ensure that a quad LNB is fitted onto the dish to enable you to run another feed from the dish to the second room.
However, if its simply the case of requiring whatever is being viewed on the Samsung to also be viewed in the second location then you could purchase one of these video sender units obtainable in places such as Argos etc, the sender being connected into the Freesat boxes rear scart socket and the receiver into the 2nd TV's similar scart socket, the signals sent via a radio link.
The other method (and similar to a Sky link) is to purchase an RF modulator to send an analogue RF signal to the second rooms TV, although this requires you to run a coax cable between both locations, the RF modulator being connected into the Freesat box in exactly the same way as the video sender, although in this case its a coax cable that's used to connect the modulator into the 2nd TV's aerial socket, and with viewing being made on the 2nd TV's analogue mode if its a dual standard TV.
By the way Sky boxes have modulators built in and they likewise do not require an additional device, Freesat boxes do not have this facility.
Looking to view different programmes in the two locations, so additional Freesatbox looks like simplest option.
The house has an aerial pole fitted to the chimney, and I may need to use the height this gives to clear some trees. Should this give generally good recepetion or would the dish be susceptible to even slight wind movement.
Paul: Unfortunately a dish is very susceptible to being moved by even the smallest amount and so that aspect will have to be considered, but as a rough guide as far as obstructions are concerned, if you stand with your back to the wall facing at about 150 degrees or so and look upwards at roughly 25 degrees from the horizontal you have to be able to have an unobstructed view of the sky.
By the way, it doesn't matter how low down your dish is and can even sit on the ground, so long as the aforementioned is achievable.
Paul - If you site and install your dish securely, it really shouldn't move unless your situation is seeing you very exposed to extreme weather conditions.
As JB38 points out,if at all possible a ground or near to ground, installation often can be made to be less obtrusive and has the advantage of ease of maintannce.
My brand new HD TV suffers picture drop-out on terrestrialFreeview (only on HD). Even though I have line-of-sight to Crystal Palace, it’s been suggested that a less compressed satellitesignal might overcome the issue. The TV accepts a direct satellite input, so I would like to purchase and fit my own dish. Can you briefly describe the ease (or not) of the alignment procedure and also the equipment required to align? Also, I understand that high qualityGerman, French, Swiss radio (music) is available via satellite. Would these signals come from a separate satellite (which please?) and if so, would an additional LNB pick-up be required? How’s it done?
I'm wondering if anyone can give me an idea of the likely cost of running a dual cable from my Sky dish into a bedroom in order to fit a Freesat PVR? The dish is situated on the wall of the room concerned.
Hi; should the LNB on my fresat dish, wobble about, my TV keeps telling me no signal avalible, and my tv go's to standby mode , this was fited by an exspert and is jusr out of warenty. I'v bourt a new top box but it's made no diffrancs what should i do next. all the best BOB.
R A YOUNG: No it shouldnt! and if the dish arm is of the round type then it suggests that the 40mm collar around the LNB has either slackened off or has even snapped, or if its a Sky elliptical dish with a rectangular arm, that where the LNB fixes to the short spigot mounting arm has come adrift.
No matter what type though, new LNB's inc fixing kits can be obtained for just over £10.00 or so from numerous e-bay sources.
I live in NE Scotland. With my Sky+box I can tune to ITV HD ('Other channels')but without having any other functionality like recording etc. Is it possible to fool my Sky+ outfit into thinking that it is situated in England - and can therefore receive ITV HD with full resources (especially recording). I am not bothered about ITV regional considerations. Thanks.
Geoffrey: The "other channels" facility is the only method you can use with a Sky+box to receive channels from another area, as unlike a Freesat box where its possible for the user to place themselves anywhere in the UK by simply entering a post code appropriate to the desired area in the set up menu, unfortunately this is not possible with Sky devices as that data is programmed into the Sky card when its sent to you, something that Sky are most reluctant to alter as they like keeping a strict check on a subscribers location.
Jack: The most likely cause is that your dish has moved out of alignment and needs re-configuring. An installer with a professioonal meter will be able to correct this and would additionally be able to determine whether the LNB was functioning correctly.
I had a free-sat system(MANHATTAN PLAZA DS.100) fitted thru the disability scheme for £29 all inclusive earlier this year. within the last couple of weeks,it has started freezing and at times losing signal altogether.This is usually when it is raining or high winds. What do i have to do to put this right please as my tv is my only pleasure now.
Thomas: Weather related problems are always associated with either the alignment of the dish or alternatively the connections to the LNB on the end of the dish arm.
The first thing to do is to carry out a signal strength test on any station that you might be viewing, because the strength / quality indications seen should both be sitting about the same levels as each other and with the level being the minimum of 50% or so, if though any of the two are under this then the dish is slightly out of alignment.
However should this test indicate that all seems to be in order, then your problem is most likely being caused by water having gained access to the "F" plug connector on the end of the coax thats goes into the dishes LNB, this requiring to be unscrewed from the LNB and then further unscrewed from the coax for purposes of drying out, then re taping with self amalgamating tape once refitted onto the LNB.
Thanks for your advice.
Ive just phoned 'EuroAerials',who installed my freesat thru the disability scheme & i was told,quite rudely, that "rain & wind will affect my signal as it has to come from a long way up in space". The woman said there is nothing wrong with the installation & its normal!!!!
Any ideas on what i can do now please?
Thomas Fuller: What you have been told by these people is just a standard line used by some of these types designed to fob you off, as wind no matter how strong, will NOT cause any problems with satellitereception unless either the dish mounting is slack, or alternatively that there is a tree located near to the dish and the wind is causing its foliage to partially obstruct the dish.
If a dish has been installed correctly, and many are not!, then only a really heavy thundery downpour can sometimes cause the signal to fail for a few minutes, but only for that very short time.
I do not at present have the manual for that model you have been supplied with, but have a look in the tuning menu for the signal checking facility and if found give an update on the indications seen, as both indicator bars (strength & quality) should be at a minimum of the equivalent of 60% for reasonably reliable reception.
Thomas Fuller: If you had equipment fitted by the BBC Help scheme then you should phone them (0800 40 85 900) as you have a 12 month after care service - they should send someone out if they can't rectify it over the phone.
My television was not used for a few days over xmas. When I switched on again I was getting no signal from the dish. I called out an engineer,he find no fault with the dish or cable, but still no signal. when he removed either of the 2 coaxes signal was restored amd the TV worked ok. He said there was a fault in the box. I have now put the coax back and everything is working. Could this be a problem with damp getting in.
I'm having a similar problem since being away for two weeks over Christmas. I have completely realigned my dish and was getting 89% quality and 92% signal readings, but the signal still fails regularly. Sometimes I can be watching a channel for many minutes with a good picture, but when I change channels there is "no signal"! Some channels have no reception at all, some I can get (almost) straight away every time. It's been stupidly damp here and although I have a silicone cover, I wonder if the moisture has still got in.
Jonathan: Well with regards to the latter possibility mentioned that could well be the case, because variations in signal levels can only really be caused by either corrosion on the "F" connector plugs threads or water having gained access to its internals, and so I would carefully unscrew the connector from the LNB then further unscrew it from the coax and wipe the inside of the connector with a tissue, likewise the end of the coax making sure that all strands are pulled back over the coax outer cover, then smear some Vaseline (although silicone grease is better) on the inner barrel and re-assemble same.
I should say that LNB's can also be responsible for exactly the same symptoms, but water problems are by far the more frequent cause.
Although it appears as though you are referring to a standardSkybox, if its a Sky + type then try swapping the "F" connector inputs over, as the problem will likely move to the recording input.
Jeanette Betts: Yes!! Microwave band signals such as used by Freesat or Sky can get completely blocked by even the slightest amount of snow sitting on the surface of the dishes LNB as the signals from the dish bowl are focussed on this spot, the proof of this being, that should the dish be within reach then once that the signals are OK again try draping a wet dish cloth across the aforementioned LNB surface and check the results, as no doubt you will find that the signal has vanished.
I have just resited myfreesat dish with quad outlets, i have used a meter to get good signal, signal and quality strength on TV both show 90% but on numerous attempts to set up tv it keeps showing "Invalid post code" or "unable to find satelite signal"
Any ideas please ?
Spike: As far as the post code is concerned some later issue post codes are not recognised by some PVR's, if of course this situation should apply in your particular case, but try entering PE6 7XZ as this is a test code I use to enable Anglia news (West) to be the default region in areas where a persons post code results in them receiving East Midlands news.
On the subject of "unable to find a satellitesignal" try swapping the two LNB inputs over on the rear of your PVR and see if this alters the message, giving an update on the result.
I am trying to installFreesat in my daughters house to replace her current Sky setup. She has 3 HD boxes and her LNB has 6 connections, they all give a perfect picture.
I have swopped each of them for a freesat box, (I have used my two from home to see if it works before cancelling sky). However the picture is very poor, with both boxes, signal is at 97% and all the channels are there. When I swop the sky boxes back the picture is back to being perfect again. I did the install on Freesat boxes from start and put in the postcode but it still does not give an acceptable picture. When I plug the Freesat boxes in back at home the picture is stunning, does anyone know why? The sky installation is only 18 months old and looks fine from the ground. This is driving me nuts, plus my daughter is paying a fortune for sky which she cannot afford. Thanks Barry
Barry Martin: A dish used for Sky reception is technically identical to that required for Freesat and so some other factor has to be involved.
When you say that the picture is inferior, in exactly what way do you mean? are the Freesat boxes HD? and if they are using HDMI connections into their respective TV's.
It would also assist to have knowledge of the Freesat brand models being referred to.
As far as the picture being OK on the Freesat boxes when tested back home is concerned, that has to be connected to the settings on your TV as the quality of a picture does not change by anything connected to the dish its being used on, because any deficiency there results in pixelation, intermittent picture freezing etc.
Barry Martin You say that the "signal" is at 97% but what about the quality reading and what figures do you get at home? I was surprised by the difference in reception between my Panasonic free to air receiver which produces better pictures than my old Fortec Star HD receivers on the same dish/LNB. Conversely when I tried a cheap 15 metre HDMI lead it was the Fortec Stars that worked better. My point being that no two receivers are the same and maybe the Sky boxes have more sensitive tuners to enable them to cope with smaller or poorly aligned dishes?
Neil Bell: Sky boxes of later manufacture (modern Sky+HD types) are generally all fitted with sensitive tuners, however this does not necessarily always apply where older Sky+ types are involved, although apart from that aspect all Sky boxes (even the oldest) give a high level of AV outputsignal for feeding into a TV compared to some set top boxes.
But though if Barry Martin found the Freesat boxes to be "stunning" when plugged in back home then this is a "no iff's or buts" case of the TV they are being connected into either being capable of producing better pictures or alternatively having been more carefully set up, although I will admit that some of the lower end LCD sets are inclined to produce a lifeless wishy washy image that's virtually impossible to improve.
Of course that is on the assumption that the inferior quality referred to is not connected in any way to pixelation or glitching? but just poor picture quality.
St Johns Cross There is no link between terrestrial and satellitereception and as far as I am aware there is no such thing as a booster for a satellite dish. All you need is direct line of sight to the satellite. So as long as there is nothing high in the sky to the SSE (e.g. trees, tall buildings etc.) of where you want to mount your dish it will work fine. The function of a signal booster for satellite reception is fulfilled by using a larger dish but as you have some sort of freeview signal and you want to receive freesat I am assuming you are in the UK and thus you won't need this.
St Johns Cross I stand corrected - You can get satellitesignal boosters but having a quick look at users reviews it seems they have mixed success with them. They sometimes work where there is a very long cable between the dish and the receiver or where people are using communal satellite systems with very weak signal strength.
I am keen to receive German free to air TV, ARD, ZDF etc...all stuff i used to watch when i loved there. I know I need a zone 2 dish but do I also need a reciver/box? I have a freeviewdigital TV already.
Hope you can advise
I have a portable satellite system for my motorhome, the kit has a small dish about 35cm. My question is, would a larger dish say 75cm be easier to align to the Astra satellite? I have heard that the larger the dish, the more difficult it is to align.
Matt You'll need a satellitereceiver as well as the dish and it would be better to go for a free to air type rather than a freesatbox as you won't need the freesat software. I'd go for an HD box because several of the German channels transmit HD free to air now and for that you'd need an HDMI cable to connect to the TV
Gordon I would have thought that a bigger dish would be easier to align because the stronger signal would give you more margin for error. I have a fairly large 1.2 metre dish & I fitted a bracket with 3 extra LNBs to receive signals from other satellites and it surprised me how easy it was to position the LNBs to get a good signal from each.
Gordon Brockley: Speaking in general terms smaller dishes are more critical to align by the fact that they aren't gathering up that much of a signal to start off with, this meaning that the slightest movement past the ideal spot will cause the signal to drop down again under the sat receivers minimum level for reception, this resulting in the classic "no signal" warning being seen.
On the other hand large dishes are capable of gathering up more of the signal and with this being why the signal strength levels seen on sat boxes with larger dishes are always that much higher to that on a box using a standard mini-dish, a knock on effect of this higher level signal making these type of dishes "slightly" (and only) easier to align.
The reason for this being, that if the dish is being swept across from one side to the other then once a signal of a sufficiently high enough level to produce a picture is found it will be held for much longer before dipping down again on the other side, in other words by them having a slightly flatter response in the pick up zone to that experienced with small dishes and their almost razor sharp responses, the smaller the dish the worse it gets.
Of course the higher signal levels associated with larger dishes is why heavy thundery type downpours do not have the same effect on satellite reception in the way they do with smaller dishes, basically because the signal has further to drop before reaching the receivers lower threshold cut off level.
The secret of success when aligning satellite dishes is really by adopting slow motion movements.
1. Is it possibe for a competent DIYer to realign a sat. dish?
2. Are suppliers of satellite equipment legally bound to give the purchaser the password to reset the system, etc.?
I bought three Freesat systems three years ago and had them fitted by a local firm. They have never been satisfactory. I can only get a few TV channels and even fewer radio channels.
My sat. boxes have a 'signal strength' and 'signal quality' page and the channels that come as 'no signal' have correspondingly low quality and strength readings. I've had the firm back to sort it out twice - once for free, but the second time for £35.00. I asked for the passwords and was told they were put in, but patently, they do not work - I can't access the boxes. I think they have witheld the passwords deliberately, fobbing me off with technical jargon, thus forcing me to pay them to come and sort out any problems.
can you help, please?