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Instructions |  Dish size? 50cm Dish Why is a Sky dish oval? A "standard" dish is taller than its width so that it is roughly circular when viewed by the LNB. It is suitable for use with a standard universal LNB with 40mm neck (but NOT with a Sky minidish LNB - read on). The larger the dish, the narrower its focal angle. Since the focal angle is more important in the "horizontal" plane, in order to reject signals from adjacent satellites, it was deemed satisfactory to have a 54cm diameter dish (widthwise) but a 43cm dish (heightwise). This is the design chosen by BskyB in the UK. However, to make full use of the total dish area, this "Sky minidish" shape requires a special design of LNB. Explanation and photos here. But FORGET "oval". It's merely the width factor I'm considering. The point I'm trying to make is that a chopped off 54cm "circular" dish has precisely the same side-rejection as a complete 54cm circular dish. Obviously it will have less gain than a full size dish and obviously the LNB has to be specially designed to match it (which is what BskyB did). So, basically, Sky took a circular dish, chopped off top and bottom sectors, rounded the corners to make it look "oval" and they got a dish with the gain of a 45cm but with the side rejection of a 55cm dish - and it was smaller than a full 55cm dish so it looked prettier.* (The fact that the gain is really too low to give a decent "rain margin" for anywhere north of Leeds is incidental!) *Note that a dish this shape - wider than its height - requires a special "Sky" LNB to get the best out of it. If you use a standard LNB that's designed to "see" a circular dish, it will be looking at two blank areas, top and bottom. This will allow the LNB to receive random background noise from behind the dish, which will degrade the signal. More about this click HERE. The Sky "minidish" is made by several manufacturers and is roughly 53 cm wide. (The wider a dish is, the less interference it will receive from adjacent satellites.) A larger "zone 2" minidish (about 55 x 75 cm) is used for northern England and Scotland where the signal (from the Astra satellites at 28.2 degrees East of true south) is weaker than in southern England. It also provides a not-too-unsightly upgrade if you are having reception problems with Sky or Freesat in bad weather. Several Astra satellites are clustered in space at the same position (within one kilometre of each other but around 22,000 miles from earth). Each satellite has a number of transmitters or "transponders" which give slightly different "beams", resulting in different "footprints" on Earth. In England, a strong signal is received from all of these transponders but, outside England, the signal becomes progressively weaker as you get further away. In some fringe areas, it's not possible to receive signals from EVERY transponder without using a larger dish. It's possible to receive signals from more than one satellite position. For example, you might want to switch between Astra at 28.2'E to Astra at 19.2'E or "Hot Bird" at 13'E. The simplest way to achieve this is to put a bracket on your dish and add an extra LNB. This can be positioned to receive the reflected signal from a different satellite position. However, the more offset the LNB is from the true focal point (where the main LNB is) the weaker the signal will be. To compensate for this, it's advisable to select a larger dish than would normally be required if only one LNB were fitted. The Sky minidish is rather small to use a second LNB and no brackets are available (but it CAN be bodged). So it's usual to buy a 60 cm dish or larger - normally 80 cm - with an LNB bracket that allows an extra LNB to be fitted. Lots of customers ask me to specify a suitable dish size... But I really can't answer such questions and, even if you give me full information, I'd still have to look at the published satellite "footprints" - which you can do just as easily as I can! However, here are some suggestions:- In the UK, for a "standard" Sky or Freesat installation with cable run no more than 25m, south of Manchester, a Sky "minidish" will mostly be OK. As you head north of Manchester or West of Bristol, consider using a larger dish (60 cm or more). North of Carlisle and West of Belfast, consider 70 - 80 cm and north of Aberdeen, larger still. Similarly, for Northern France, a standard "minidish" (nominally 53 cm) will do but, as you head south, you can combat problems with "rain fade" better if you increase the size, aiming towards 90 cm at the Spanish border. Paris, Brussels and Amsterdam fall within the "50cm" footprint but a larger dish will be required for reliable reception of all programmes as you move east of Amsterdam and south of Paris. However, you'll still receive some programmes quite a long way east and south (at the time of writing - mid 2012). If your cable run is longer than 25m but less than 50m, or if you are using a "Quattro" LNB with a "multiswitch", use the next larger dish size. Using a larger dish is MUCH more likely to give good results than using an amplifier, but, with an LNB cable run greater than 50m, use both. Note: Astra 2D was replaced by Astra 1N, which was replaced by Astra 2F on November 20, 2012, so we have no specific information at present. To look up dish sizes click on this link: http://www.lyngsat.com/28east.shtml This page lists satellites and programmes from the Astra satellites at 28.2'E The page shows recommended dish sizes but bear in mind that they may not be correct for your specific location as there are "hot spots" and "cold spots" in signal strength. For example, you may receive programmes in Tenerife with a suitable size dish, LNB and receiver *if you get the combination right*. For Sky Digital you can read my book "Installing Sky Digital TV and Freesat" which holds 120+ pages of hints and tips from professional installers, as well as pages and pages of reports from Sky Digital viewers as far away as Africa. Read what they have to say about dish types, sizes and LNBs then make up your own mind. If you can afford to, always err on the large side and remember that the type of LNB, receiver and cable (and cable length) can all make a big difference to the results. For HOT BIRD at 13'E click here: http://www.lyngsat.com/hotbird.html Click on the links in the column labelled "Beam" to see the individual footprints of the various Hot bird satellites. Sky Digital in Spain (and southern Europe) Salvador Ferrairo Castella spent weeks carrying out tests with various LNBs and dishes. This book is a report of his findings. What size of dish and which LNB works best and why? Complete with photographs including the dishes, LNBs, the ground station where he did the work and the equipment that he used to analyse the signals. Computer plots showing the differences between transponder spectra. This book is full of technical information but Salvador writes in impeccable English with a style that makes the book easy and interesting to read. You can feel his excitement as he reports on his findings! Absolutely invaluable for any expat in southern Europe. What are the relative advantages / disadvantages of the different materials used for satellite dish manufacture - steel, aluminium, mesh, plastic etc.? Steel is cheap but rusts unless very well protected. Good microwave mirror properties. Aluminium is expensive but is easier to press to the correct shape and doesn't rust. (However, it will corrode in the presence of salt water unless well protected.) Good microwave mirror properties. I'm frequently asked about painting dishes. YES you can paint the entire dish any colour you wish, including the LNB and cable. Don't paint the LNB cap which faces the dish. After you have checked your dish for damage and missing parts, we STRONGLY advise you to paint it. Done properly, a couple of coats of paint will help protect it from corrosion and suitable choice of colour(s) will help it blend into its background. Although white is a nice colour if your building is white, it reflects the sunlight too efficiently. In countries where sunshine is strong and continuous you should paint the dish a dark colour with matt (not gloss) paint. If the dish concentrates sunlight on the LNB cap, it will melt! Camouflaged dishes and unusual satellite antennas are discussed in this book.... Will an amplifier improve my signal/picture? CLICK HERE to find out Dear Martin I read with interest the piece in your newsletter on Astra 2D channels dropping out at random on the Panasonic Digibox and the Panafix2d filter solution. I've had this problem for ages on 2D, but with a Pace 2500. My complete system is : Cambridge G57 'platinum' LNB, 1 metre solid offset dish, Cryptik DiSEqC motor, about 40 metres of CT100 connected to an Echostar DSB-808 then the LNB loop through to the Digibox. It's certainly no lack of signal - I live in the London area! The Echostar TP signal strength meter indicates between 85 and 90% for Astra 2A/B and Eurobird, dropping to between 80 and 85% for 2D. Dish alignment can't be bad as I can get all expected satellites for a 1m from 45E to 30W (whereafter trees come into play). It's also not TP specific. I can have problems getting one or more channels whilst others on the same TP are fine. The only solution at present is as you say by channel switching until the one you want comes up. I would be interested to know if you think this filter would help on the Pace. Regards Steve Potter I think it unlikely. The losses in your cable coupled with the connections to the DiSEqC motor may be causing the problem. Try connecting directly to the LNB with the shortest possible length of coax. 40m is really on the top limit. Best Wishes, Martin Hi Martin Thought I'd drop you a note to say thanks for the tip. Unfortunately due to geographic location (rear of house faces due south) and the wife (AV equipment in the front room, please) shortening the cable was not a real option. I managed to loose about 4 metres with a bit of re-routing! So, I had the ever efficient Nicola dispatch me a Global TVRO16F. This made only a marginal difference to the 2D channel switching problem, but made a big improvement to signal stability, especially on marginal channels such the Italian ones on the Eurobird S2 beam. Of course now we have plenty of BBC FTA channels to observe, channel switching with the Echostar is not a problem - it never fails to lock on to 2D channels unlike the Digibox. As a matter of interest I recently upgraded the Echostar software to EchoNav v3.01 from v2.2 and experienced a problem that neither the dealer nor Eurosat were able to explain, but came up with a workaround. After about 2 days, having selected DiSEqC 1.2 motorised from a factory reset, it would revert to the default Fixed Dish setting, making further sat positioning impossible without another reset. The workaround is to select 2 LNBs with DiSEqC 1.2 (just in case you come across anyone else with the problem). Kind regards -- Steve Potter August 27, 2003 Thanks for the info. The TVRO16F is supposed to be fitted after about 40m of cable so I'm interested to know where you positioned it as, in general, attaching it behind the receiver is not recommended! I'm receiving more reports of 2D problems with Pace Digiboxes but, as I don't have one here to investigate, I'm no closer to a solution. I have a suspicion it may be yet another symptom of the ZIF tuner problem. Best Wishes, Martin Aug 29th 03 Dear Martin Before I fitted the TVRO16F I called Global and asked if it should be at the receiver or LNB end - they said it didn't matter! So of course I took the easy option and it is behind the receiver. For sure it has stopped at lot of the picture break-up problems on weaker signals. I did a straight comparison, with and without, checking the Echostar signal quality meter and without the TVRO16F the level would be about say 60%, then drop for a second or so to 30%, then go back to 60%. With the TVRO16F it remains stable. However I did wonder if the TVRO16F was the factor with the Echonav 3 problem, even though it had not been a problem with 2.2. Are you thinking I should fit it at the LNB end - if so, between the motor and LNB or after the motor? Steve No, as I recall from about 13 years ago, they told me it should "after approx. 40 - 45m of cable for best results". I was just curious. It's a trade off between amplifying noise and amplifying signal. If it's close to the dish then it will be amplifying more signal than noise but, since the signal is already strong, it may be overloaded. Further from the LNB, the cable has picked up noise and the signal is weaker so both get amplified. You might like to try it at or near the LNB. Martin Pickering Dear Martin Having fitted the Global TVRO16F between the LNB and motor as you suggested I am no longer experiencing the Astra 2D channel switching problems on the Pace 2500. I left it a while to try it in different weather conditions and times of day. Finally we have some heavy rain and it's still switching channels no problem. Kind regards Steve Potter Sunburn For a few days during the months of March and October, around 10am, the sun goes directly behind Astra 28.2'E. (Useful for alignment purposes.) This can have two effects: Here's a useful site that gives you dish sizes:
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