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Technical Section page 8a

LNB mysteries explained - part 2 Send this page address - CLICK HERE - to a friend ! Please read Part 1 first. Low Noise Block-downconvertor (so called because it converts a whole band or "block" of frequencies to a lower band). ============================ List of LNB types:  1) Standard LNB 10.0 GHz L.O. Often called a "Marconi switching LNB". Works in one band. Noise Figure usually 1.0 dB or better but older "Blue cap" types can be much worse. Integral feed horn, usually with 40mm neck but flange type available to special order and other neck sizes have been made (especially 22.5mm). Marconi also made a "Bullet" shape LNB of this type that used a PTFE insert instead of a horn. Polarisation switching is controlled by dc voltage supplied by the receiver. 12.5v to 14.5v gives vertical and 15.5 to 18v gives horizontal polarisation. A higher voltage than that can damage the LNB. A voltage that is too low will prevent the LNB from working correctly. 2) "Enhanced" LNB 9.75 GHz L.O. The Cambridge "Juno" AE6 is an example of an "Enhanced" LNB, having a Local Oscillator of 9.750 GHz. Works 10.7-11.7 GHz. Noise Figure usually 1.0 dB or better. Integral feed horn with 40mm neck. Normally used with later type receivers that have a 2GHz tuner but no 22kHz signal generator. Designed specifically for Astra satellite reception from satellites 1A, 1B, 1C and 1D. Polarisation switching is controlled by dc voltage supplied by the receiver. 12.5v to 14.5v gives vertical and 15.5 to 18v gives horizontal polarisation. A higher voltage than that can damage the LNB. A voltage that is too low will prevent the LNB from working correctly. 3) "Universal" LNB 9.75 and 10.60 GHz L.O. The Cambridge "Platinum"Geo Universal G57" LNB Works in 2 bands* 10.7-11.8 and 11.6 - 12.7 GHz. (22 kHz signal switched). Noise Figure usually 1.0 dB or better. Integral feed horn with 40mm neck but flange type available to special order. *If your receiver tuning range is less than 2.15GHz you will have a gap between high and low bands. Refer to calculations, below. In effect, this is a "Quad Band" LNB. A Universal LNB requires a 22kHz signal at 0.5v p-p to switch its Local Oscillator to 10.6GHz ("high band"). Otherwise it uses its 9.75GHz oscillator. Polarisation switching is controlled by dc voltage supplied by the receiver. 12.5v to 14.5v gives vertical and 15.5 to 18v gives horizontal polarisation. A higher voltage than that can damage the LNB. A voltage that is too low will prevent the LNB from working correctly.   "DBS" LNB 10.75 GHz L.O. Normally bolted to a separate polariser and feed horn. Works in one band: 11.7 - 12.5 GHz. Receiver with standard 0.95 - 1.75GHz tuner may be used. Noise figures vary. "Telecom" LNB 11.0 GHz L.O. Normally bolted to a separate polariser and feed horn. However, Marconi made a voltage-switching version with integral feed horn*. Works in one band: 11.95 - 12.75 GHz. Receiver with standard 0.95 - 1.75GHz tuner may be used. (* identified by a serial number label with a red corner, although some were incorrectly marked). Noise figures vary. "Dual band" LNB Normally bolted to a separate polariser and feed horn. Works in 2 bands 10.9 - 11.7 and 11.7 - 12.5 GHz. Receiver with standard 0.95 - 1.75GHz tuner may be used. Band switching achieved by supply voltage of either 14 volts or 18 volts. Noise figures vary. "Tripleband" LNB Normally bolted to a separate polariser and feed horn. Works in 2 bands 10.9-11.8 and 11.8-12.75 GHz. Receiver with 0.95 - 2.0 GHz tuner should be used. Noise figures vary. "Quadband" LNB Normally bolted to a separate polariser and feed horn. Works in 2 bands 10.7-11.8 and 11.7-12.8 GHz. Receiver with 0.95 - 2.05 GHz tuner should be used. Noise figures vary. "Twin-output" LNB Currently available in Standard, Enhanced and Universal form, the twin output LNB provides two outputs to feed two separate receivers. Each output can be switched by 13/17 volt input by the individual receiver to change polarisation. "Dual-output" LNB Was available in Standard and Enhanced form, the dual output LNB provided two outputs to feed two separate receivers. Each output had a fixed polarisation; one horizontal and one vertical. This type of LNB was used with switching boxes such as the "Mini Magic" which could feed four separate receivers. This type of (obsolete dual-output) LNB is no longer used in the UK and Europe, having been superseded by the "universal" type. Therefore a "mini magic" distribution system is no longer available. Instead, you should use a "quad-output" universal LNB or, if you need more than four outputs, a "quattro LNB" plus a (expensive) head-end distribution system which will usually feed up to at least 12 (sometimes 16) receivers. Note that a "twin-output" LNB is frequently (and incorrectly) called a "dual-output" LNB in the USA and sometimes even in the UK and Europe. Care should be taken when ordering! A "Dual LNB" usually refers to a "monobloc" or "monoblock". "Dual LNB" or "Monobloc LNB" Comprises two universal LNBs fixed together at a small angle in a single housing. Only one "F" connector is used. A single coaxial cable connects to the Digital (or Digital + Analogue) receiver which must be able to use DisEqC signalling to select which LNB is to be used. Normally used on an 80cm dish to receive Astra at 19.2'E and Hotbird at 13'E (but not simultaneously). monobloc setup monobloc setting up This type of LNB has a single output and the actual satellite signal is selected by the receiver which sends a DisEqC (22kHz) tone up the LNB cable. So only one satellite transmission can be viewed at a time. This is in contrast with dish systems that have two or more separate LNBs where, with two receivers, both satellite transmissions can be viewed or recorded simultaneously. See picture HERE. "Quad-output" or "Quad universal LNB" This can feed four separate receivers. Each receiver has independent control of polarisation and band via 13/17v switching and 22kHz o/off respectively. This LNB is used with the new Sky Digiboxes that have two LNB inputs and internal Hard Drives for recording a programme while you watch another. Two LNB outputs go to this "Sky Plus" Digibox and the other two LNB outputs can go either to two standard Digiboxes or to one other "Sky Plus" Digibox. "OCTO" LNB As above but with eight independent outputs. "Quattro universal LNB" This has four fixed outputs and is used only in "head end" I.F. distribution systems for apartment blocks. One LNB supplies a head end unit that can provide (typically) up to 16 outputs for separate Digiboxes. The four outputs of the LNB are as follows:- 1. Horizontal polarisation low band 2. Horizontal polarisation high band 3. Vertical polarisation low band 4. Vertical polarisation high band You should not connect any of the outputs, 1 - 4, directly to a receiver unless you want to restrict viewing to just one of the four options. Even if you do, the receiver may not work. It's not a good idea. Use the Quad instead. "DirecTV LNB" This is what the Americans confusingly call a "Dual Output DBS LNBF" and has a local oscillator frequency of 11.25 GHz. It is not compatible with UK systems and it's not available in the UK or Europe. I suspect that "dual output" is what we call "twin-output" but that makes me wonder what they call our "dual-output" LNB! Input Frequency - 12.2 to 12.7 GHz   Output Frequency - 950 to 1450 MHz   Noise Figure - 1.1 dB, Max   Gain - 50 to 62 dB   LO Frequency - 11.25 GHz, ± 2 MHz It is entirely different from LNBs used in the UK and Europe in that it has a single internal oscillator running at 11.25 GHz whereas our "universal" LNBs have two selectable oscillators running at 9.75 and 10.6 GHz respectively. See the following page:- http://www.calamp.com/pages/pb_part.php?prt_id=32 Is there actually a different LNB for prime focus dishes + offset dishes? Surely an LNB's innards are the same and the feedhorn or the C120 flange is the only difference? In the old days, LNB noise figures were high, the gain (amplification) was low and satellite transponder power was typically 20 Watts. Imagine trying to see a 20 Watt light bulb 24,000 miles away! (You'd have trouble seeing a 20W bulb at the end of a 24 yard corridor). So, an LNB and feedhorn had to be matched to the dish. The open end of the feed horn LNB had to be at the exact focal point of the dish and the horn had to be flared in such a way that, with it at the focal point, the horn could "see" the exact circular area of the dish - no more and no less. If it was less then it wasn't collecting signal from the full area of the dish. If it was more, it was also collecting unwanted "noise" from any warm object (wall) or from the sky behind the dish. A good compromise was to take just part of a much larger paraboloid dish and mount the LNB in an "offset" position. The curvature of this partial dish is such that the focal point is now much lower so the LNB and feedhorn no longer obscure the signal path as they would with a "prime focus" dish. Nowadays, satellite transponders can produce typically 50 or 60 Watts and LNBs have higher gain and lower noise figures. With these strong transmissions, you can get away with murder. People stick any old thing on the end of the boom arm - which rather explains why one man's 0.6dB LNB is another man's nightmare when the signal strength is not optimum! The Sky minidish, for example, is a compromise between size and performance. It's very important that the LNB matches the dish exactly. This is one good reason why the dish comes with its own LNB. The manufacturers might "fudge" the issue if asked. After all, if they admit that their LNB works best with, say, an 80cm Lenson Heath dish and you just bought an 1 metre dish made by someone else, you might not be too happy. If you "mix 'n' match" by picking a 60cm dish and a Universal LNB at random, the chances are that the performance could be no better than that of the Sky minidish. As a general rule, any standard LNB will work with a circular (prime focus) dish or an offset focus dish which is taller than it is wide (which "looks" circular when viewed by the LNB). However, a dish which is wider than it is tall will need a special LNB. Just to prove the point, here is a typical "Universal" LNB used with a Sky "minidish". The minidish is oval in shape, being much wider than it is high. Inside that plastic rain cover is the actual LNB. Note the difference in scalar ring height (red arrows). The side projections allow the LNB to focus on a wide area in the horizontal plane, while the top and bottom projections are longer and focus the LNB on a narrower area in the vertical plane. This LNB is designed specifically for an oval dish and will give very poor results with a dish that is roughly circular or a dish that is taller than it is wide. Here's another comparison. The SX1019 on the left has circular scalar rings inside the feedhorn. It is designed to be used with a nearly circular dish. The SX1019/S on the right is designed specifically for a Sky minidish which is wider than its height. This type of LNB can also be used with a Raven dish of a similar shape to the Sky minidish. Both LNBs are made by Philips. The one on the right, however, is branded "Skyware". Sky "Minidish" upgrades Here is the Philips SC519QS/S Quad output LNB as supplied with the SKY-plus system with adaptors for the "minidish". The red arrow points to the special oval shaped "scalar" steps in the feedhorn. These cause the LNB to focus exactly on the oval shape of the "minidish", using the full dish area but without picking up reflections from the wall behind. Some dealers, who are either unscrupulous or simple know no better, are offering a standard Twin-output or Quad output LNB with an adaptor to fit the "minidish". The adaptor fits a treat. Unfortunately, the LNB will not give optimum performance - resulting in "rain drop-out" during bad weather. Although the Philips SC519QS/S Quad output LNB kit *is* available, it is rather expensive. If you *must* use the "minidish" (and there are good aesthetic and environmental reasons to do so) then you'll have to pay the price. However, you may prefer to buy a standard dish of, say, 60cm diameter and use a standard 40mm neck twin-output or quad-output LNB with this. The match and fitting will be perfect and the "rain drop-out" will be very rare. The price of a 60cm dish with twin-output LNB will be less than that of a Philips SC519QS/S Quad output LNB kit . >Hi, just a quick question.............I have a new panasonic digibox and I >want to connect my old pace upstairs for kids. I have a sky mini dish and >need a twin LNB...........is it best to replace dish with 60 cm and its own >twin to compensate in loss of signal by splitting or is it just as good to >replace cambridge LNB with a twin-output one..if so which one/how much?? > >many thanks, Tim. There is no loss of signal because a twin-output LNB is a true twin-output - it doesn't "split" the signal in half. Both LNB outputs are fully independent. So the minidish will be as good as ever (although you may need to realign it because of the extra weight of the LNB which will bend the arm slightly.) The other consideration is cost. There is no twin-output LNB available with fitting kits for all three types of Sky "minidish" so you will have to buy the twin-output LNB for your specific dish (if available) or the special (expensive) "quad-output" minidish LNB or, alternatively, the cheaper twin-output LNB with 60cm dish. Not much to choose between them but the 60cm dish *will* reduce signal loss in bad weather. If you don't ever suffer from this then stick with the minidish. Refer to my accessories catalogue for prices. Virtual-Book: Installing Sky Digital TV Companion book to the free "Understanding..". Essential reading if you want to move your old system to a new house, install a brand new Sky-Plus or standard system, fit a system to your motorhome, caravan or narrow boat or use it in Europe, this book answers your questions. What size dish, what sort of cable, connectors, which receiver is best ... 110+ page book filled with colour photographs and easy-to-understand explanations. I guarantee you'll be delighted with this amazing book full of information! People keep asking me if they have a "universal" LNB. It's easy to find out: If it came with a Sky Digital system, it's a "Universal" LNB, meaning that it has a 9.75 GHz internal oscillator for "low band" use and a 10.6 GHz oscillator that is selected by feeding a 22kHz tone to it for "high band" use. Many such LNBs actually have the word "Universal" printed on them. A Universal LNB requires a 22kHz signal at 0.5v p-p to switch its Local Oscillator to 10.6GHz ("high band"). Otherwise it uses its 9.75GHz oscillator ("low band"). Polarity switching is controlled by dc voltage supplied by the receiver. 12.5v to 14.5v gives vertical and 15.5 to 18v gives horizontal polarisation. A higher voltage than that can damage the LNB. A voltage that is too low will prevent the LNB from working correctly. A lot of motorised systems use a Universal LNB nowadays. This is good from the point of view of ease of installation and adjustment but it really is a compromise if you are dealing with any weak signals. Where a weak analogue signal might give a picture with terrible "sparklies", a weak digital signal can give a blank screen and no sound. You need to cut the losses as low as possible and provide an accurate adjustment for "skew" which is the rotational angle at which your dish receives the signal from the satellite. You can fit a C120 flange LNB with a magnetic (coil) polariser and this will allow fine adjustment of skew (if your receiver provides it). However, a magnetic polariser has losses and a mechanical polariser is better in this respect - again provided that your receiver can drive it. Even though we are looking at something like only 0.1dB improvement, this can make the difference between receiving a watchable digital transmission and receiving a bunch of coloured squares. Most digital receivers can NOT use a polariser. Another problem in choosing an LNB is that most manufacturers quote an "average" or "typical" noise figure. The first point to note is that your particular LNB might have this noise figure at a particular frequency but could be significantly worse at other frequencies. Even if you get a print out of the actual noise figures and gain performance when you buy your LNB, you have to bear in mind that these measurements were made in a factory under ideal conditions with the LNB receiving (probably) 18 volts and feeding an exact impedance of 75 Ohms. Of course, your cable is *supposed* to be 75 Ohms and your satellite receiver tuner input is *supposed* to be 75 Ohms but are they? In fact they seldom present exactly 75 Ohm impedance at all frequencies. Just like the LNB, the figure is "typical". Worse, it can be affected quite drastically by kinks and joints in the cable and, of course, by anything you insert, such as an in-line connector, amplifier, switch or (aagh!) splitter. What happens if the impedance is not exactly matched? Well, I'm not going to launch into a highly technical explanation of Voltage Standing Wave Ratio (even if I could!) Suffice to say that part of the signal gets reflected back. This can have the effect of cancelling out part of the signal with inevitable results. So how do you choose your LNB? It's best to go on recommendations. If a particular type of LNB shows good results with a specific make and size of dish, try that combination. Buy the best quality cable you can afford. Avoid kinking it and keep the run as short as possible. Avoid joints if at all possible. If you have to use a switch, choose one by a good manufacturer such as Global Communications in the UK. Fit the 'F' connectors carefully, making sure that the copper braid screening is clamped evenly all round. (Avoid any sort of connector or wall plate that uses a screw to clamp the inner core. There is no way that this can be properly screened or maintain an impedance of 75 Ohms. It may work fine for UHF TV aerial signals but I wouldn't trust it with satellite TV.) Finally, remember that the dish size, cable quality and the overall matching of LNB, dish and cable has FAR more effect on a weak signal than the actual noise figure of the LNB >I'm living in the Balearics and have a 1.2 metre dish for Sky,and am >contemplating getting a 0.4 db LNB to improve reception of the "difficult" >channels i.e. the ones that fade away at certain times of day such as ITV >....will this be worthwhile. >Also does anyone in the Spain area get MUTV...it's for free til 18th dec. >and I still can't get it... "no satellite signal" is the sad result of >trying to tune in.... The difference between a 0.6dB LNB and a 0.4dB LNB (even if such a thing really existed) is going to be so small as to make no difference to your problem. What you have is a serious lack of signal strength at certain times of day and only a larger dish will improve upon that situation. Why do I say that a difference of 0.2 dB is neglgible? Well, I'm not a mathematician and those who are will certainly correct me on the calculation but 3dB represents 50 percent signal difference. dBs use a logarithmic scale so 0.2 dB represents something like one hundredth of that - in other words 0.5 percent! So you pay £100 to gain 0.5% ? Heck, you could get the same improvement by chopping a metre of cable off. On the other hand, if you take a 1.2 metre dish as being circular, for the sake of easy calculation, its area is pi x R x R where R is the radius (= 60cm). That's 3.142 x 3600 = 11311 square cm. A 1.3m dish in comparison has an area of 3.142 x 65 x 65 That's 13275 square cm The difference between them is (13275 - 11311)/11311 x 100 % That's over 17 percent improvement. So increasing your dish size by just a small amount will increase the signal collection area by a very usable amount - 17% in this case. That's probably not enough to solve your problem so think of going even larger. A 1.5m dish will have an area of 17674 square cm That's an improvement of 6363 square cm or 56 percent over your 1.2m dish! See the point? The LNB noise figure is irrelevant. You can also increase the amount of signal reaching your receiver by:- Using the shortest possible length of coaxial cable. Using the lowest loss cable you can buy. Where does the LNB go ? Once a month someone buys a "bargain" dish, from a car boot sale or a "trusted friend", with bits missing and asks me "how long should the LNB support arm(s) be and exactly where should the LNB be fitted? If it's an oval offset focus dish with the LNB arm at the bottom, you are snookered. Throw it away. If it's a circular prime focus dish the LNB has to be in front of the centre of the dish and the entrance to its feed horn has to be at the focal point. You can find this by putting the dish on the ground, facing directly towards the sun (as near overhead as possible) and holding a piece of white card above the dish centre. Move the card away from the dish, watching the reflection of the sun on the dish-side of the card. When the sun is focussed to a small spot, that's the focal point, as near as you'll get it. What sort of LNB ? People keep asking me what sort of LNB they have. It's easy to find out: Align your dish on the Astra satellite cluster at 19.2'E. Set your analogue receiver LNB installation menu to 10.0 GHz (not adjustable in older receivers so you can safely assume it's already fixed on 10.0 GHz). Now check the current listings for Astra at 19.2'E and select a program at, say 11.244 GHz Horizontal. (This is currently "RTL shop") If you see the correct programme when you tune your receiver to 11.244 GHz Horizontal then you have a 10.0 GHz LNB. If you find this programme 0.250 higher at 11.494 then you have a 9.75 GHz LNB ("enhanced") or maybe a 9.75/10.6 GHz LNB ("Universal"). The only way to determine whether an LNB is "universal" is to supply it with a 22kHz "signal" and see if the picture disappears (it switches to "high band"). However, most Universal LNBs are clearly marked either "Universal" or "9.75/10.6". What's the Best LNB ? People ask me all sorts of weird questions. One of the favourite is "what's the best LNB for my dish?" I can't answer that. Firstly, the LNB has to match the *receiver* as well as the dish. Secondly, LNBs vary a lot in their design and no manufacturer is going to admit that his LNB is good on (say) a Lenson Heath dish but crap on a Channel Master dish. So the only way to find out is to try it. Thirdly, LNBs vary *in the same production batch* so one might be good for borderline signals while another is not. And we have no way to measure them. "Are your LNBs new?" Well, they are as new as we can get. They come straight from one of several trade distribution warehouses and they get them direct from manufacturers or importers. They might have been lying on the shelf for months but we have no way of telling. "What's the gain / noise figure / temperature variation / phase noise ..? Please ask the manufacturer. We don't have these figures to hand. <--- Magnetic polariser 4) Old standard "FSS" LNB 10.0 GHz L.O. Normally bolted to a separate polariser and feed horn. Works in one band: 10.9 - 11.7 GHz. Receiver with standard 0.95 - 1.75GHz tuner may be used. Noise figures vary. Very old ones can be 3.0 dB!   Testing LNBs Test equipment costs thousands of pounds and it takes time to check an LNB across its entire frequency range. So how to test an LNB ? The only way you can test an LNB is to fit it to a dish, align it on a satellite and connect it to a receiver. Then make sure that every channel is receivable. Even then, it may not show up an intermittent fault. Some Panasonic receivers are "allergic" to certain LNBs. Our "panafix2d filter" will cure this. Explanation of (L.O.) Local Oscillator Frequency: Suppose a signal comes from the satellite at a microwave frequency of 12 GHz but your typical receiver tunes up only to 1.75 GHz? (Also bear in mind that most cable will NOT happily pass frequencies much above 2GHz). The function of the LNB is to reduce the frequency of the satellite signal. It does so by subtracting a frequency figure from the satellite signal frequency. This figure is called the "Local Oscillator" frequency ("LO") of the LNB. So an LNB with a LO of 10.25GHz will send a 12GHz satellite signal down the cable at 1.75GHz (just within range of your old receiver). 12GHz - 10.25GHz = 1.75GHz Working in reverse, if your highest satellite frequency is 12.6 GHz then you will need an LNB with a LO of at least 12.6 - 1.75 = 10.85GHz in order to reduce the satellite signal to a frequency that your receiver can "see" (1.75 GHz). Now let's reverse the process again: A "standard" LNB has a LO of 10.0GHz. So the highest satellite program frequency that your standard receiver can *see* is 1.75 + 10.0 = 11.75GHz An "enhanced" LNB has a LO of 9.75 GHz 1.75 + 9.75 = 11.50GHz A "universal LNB has TWO LOs. One is 9,75 (same as "enhanced") The other is 10.6 which is selected if it "hears" a 22kHz (just above audio) signal. 1.75 + 10.6 = 12.35GHz Of course, if your receiver can accept signals up to 2.0 GHz then the highest acceptable signal frequency becomes 2.00 + 10.6 = 12.60GHz And a receiver with a tuner that extends to 2.15GHz achieves 2.15 + 10.6 = 12.75GHz (which happens to be the top of the "Telecom" band!) Now, you are still puzzled about the DBS LNB This has a LO of (typically) 10.75GHz So an old 1.75GHz receiver will get up to 1.75 + 10.75 = 12.50GHz A final consideration has to be the LOWER limit on tuning: Most old receivers can tune no lower than 0950 MHz (= 0.95GHz) whereas later ones might go down to 0.70GHz. Check out the above calculations with these lower tuning range limits to see the overall tuning bandwidth for any receiver. This is all very basic "sums" - nothing complex - so once you have a "picture" of what is happening, you can sketch little band plans for any combination of receiver annd LNB. Once you know the value(s) of the LO(s) in the LNB and of the upper and lower tuning limits of the receiver in question, you can quickly figure out what can be received. NOTE: Older receivers *expect" an LNB with a 10.0 LO and the frequency display is arranged just for this. However, you can use an LNB with a different value LO. It just means that the *displayed* frequency will be incorrect. Transponder - LNB Local = tuner frequency Frequency Oscillator     12750 MHz | | | Telecom/Astra 1F | | | DBS/Astra 1E | 11700 MHz - 10000 MHz = 1700 | | | Astra 1B | | | | Astra 1A Receiver tuning range without ADX | | | Astra 1C | | 950 + 500 = 1450 | Astra 1D | | Tuning range with ADX | | 10700 MHz - 10000 MHz = 700 + 500 = 1200 An old standard receiver usually tunes from 950 to 1700 MHz. The map above shows the limited tuning range of an old standard receiver with an old standard 10.0 GHz LNB. The addition of an ADX Channel Expander moves the Astra 1D frequencies up by 500 MHz into the tuning range of the receiver. To receive all Astra channels from satellites D to B without using an ADX, a receiver would need a tuning range of 700 to 1700 MHz. Transponder LNB Local Frequency Oscillator     12750 MHz - 10600 MHz = 2150 | | | | | Telecom/Astra 1F | | Receiver tuning range for Hi band (22kHz on) | | | DBS/Astra 1E | | - 10600 MHz = 1100 11700 MHz - 9750 MHz = 1950 | | | Astra 1B | | | | Astra 1A | | Receiver tuning range for Lo band (22kHz off) | Astra 1C | | | | Astra 1D | | | 10700 MHz - 9750 MHz = 950 An Enhanced LNB has a local oscillator frequency of 9750 MHz. The receiver now needs a tuning range of 950 to 1950 MHz as shown in the map above. If a Universal LNB is used, its local oscillator can be switched from 9750 to 10600 MHz by sending a 22kHz signal up the cable. Some receivers have this facility built inside. Some will need an external signal-inserter box connected into the cable. If the receiver has a range of 950 to 2150, it will be able to receive programmes on both Hi and Lo band. Another possibility is to use an ADX-Plus. This has an internal switch which, when moved across, makes the ADX-Plus move the frequencies DOWN by 500 MHz instead of up. So a channel at 12750 MHz is moved down like this: 12750 - 10600 - 500 = 1650 MHz (with an ADX-Plus) which is well within the tuning range of an old standard receiver. And the lowest channel receivable will be: 950 + 500 + 10600 = 12050 MHz (with 22kHz signal ON and ADX-Plus) By fiddling with the ADX-Plus switch and the 22kHz signal inserter you can probably receive the full range of channels if you have a Universal LNB and a standard receiver! Note: MHz (MegaHertz) = GHz (GigaHertz) x 1000 So 9750 MHz = 9.75 GHz Please let me know if you have any other thoughts on this and maybe we can add it to the FAQs. >Martin, > >Many thanks, I took your advice and sat down with a pen and post-it >note, and went through your LNB FAQ. Very informative thanks. > >I think I've got it sussed! If you don't mind, I'd just like to clarify >my understanding: Sure. That's the idea. >Having establish that I've got a "Universal" LNB it has two L.O. frequencies - >9750 MHZ and 10600 Mhz. I now understand that these values represent the >degree to which the received frequencies are shifted by (reduced by). Yes. >The tuning frequency of my receiver with it being an old Amstrad SRD400 >is probably: 950 Mhz to 1700 Mhz a range of 750Mhz. Yes :o) >Astra broadcast frequencies range from 10700 Mhz (Astra 1D) through to >11700 Mhz (Astra 1B). So I need to calculate which of these frequencies >each of the two L.O.s on the LNB in conjunction with the tuning range >of the receiver, I can receive, thus: > >L.O. 1 of 9750 Mhz > >950 Mhz (lower tuning capabilities of receiver ) + 9750 Mhz (L.O. 1) >= 10700 Mhz >1700 Mhz (upper tuning cap. of receiver) + 9750 Mhz (L.O. 1) = 11450 >Mhz. > >Hence able to receive frequencies of 10700 Mhz to 11450 Mhz. > >L.O. 2 of 10600 Mhz > >950 Mhz (lower tuning capabilities of receiver ) + 10600 Mhz (L.O. 2) >= 11550 Mhz >1700 Mhz (upper tuning cap. of receiver) + 10600 Mhz (L.O. 2) = 12300 >Mhz. > >Hence able to receive frequencies of 11550 Mhz to 12300 Mhz. > >Being an old crappy Amstrad SRD400, I presume my receiver isn't able to >signal the LNB to switch to the upper of the two L.O. frequencies, so I >can't access anything above 11450 Mhz. With a 22kHz signal inserter I should >therefore be able to access 11550Mhz - 12300Mhz? You are doing OK so far. >However, this leaves a gap in the middle between 11450 and 11550 of >frequencies which I can't access! Presumably with an ADX (and 22kHz signal >inserter) I can shift those frequencies into tunable ranges? > >Presumably, all I need now is an ADX and a 22kHz signal inserter in order to >receive all Astra frequencies (and then some ... )? Oh yes, and a Sky >subscription :-) You don't really need a 22kHz signal inserter. >Would I be better off buying an ADX plus, so that I shift the >frequencies down rather than up? So as to ensure my receiver is happier >about it? Yes, I would think so. There's nothing on the higher frequencies for your Amstrad to receive from Astra at 19.2 degrees East. Sky Sports 3 would be the highest useful channel, with a couple of foreign stations just above that. >How much would I expect to pay for an ADX and 22kHz signal inserter? If you have a Sky subscription they will post you an ADX-Plus for just £9.99. Otherwise you can buy one for £12.95 upwards. >Many thanks for all your help. It all seems so much simpler now. Or have >I missed something? Nope. I told you it was simple. People become frightened because they think it's too technical. The truth is that you simply need to be able to add and subtract - roughly to primary school level or lower! You don't need *any* technical knowledge. Just realise that there are various ways to add or subtract the frequencies. Specifically: there are various fixed values that you can use - Typically 10.00 GHz, 9.75 Ghz, 10.6 Ghz etc. for an LNB. Also +0.5GHz and -0.5GHz for an ADX-Plus Channel Expander, dependent on its internal switch position. Virtual-Book: Installing Sky Digital TV Companion book to the free "Understanding..". Essential reading if you want to move your old system to a new house, install a brand new Sky-Plus or standard system, fit a system to your motorhome, caravan or narrow boat or use it in Europe, this book answers your questions. What size dish, what sort of cable, connectors, which receiver is best ... 110+ page book filled with colour photographs and easy-to-understand explanations. I guarantee you'll be delighted with this amazing book full of information! Send this page address - CLICK HERE - to a friend ! Copyright ©1998 Martin Pickering Version 1.5 updated on January 12, 2002 This file may be downloaded for private and personal use but NO part of it may be published in any form without the prior permission of the author. This Web Site was produced entirely on a Macintosh computer

©2004 SatCure

A Beginner's Guide to Receiver Repair Based on the original "Screwdriver Expert's Guide to Satellite Receivers" this eBook describes the basic components and a typical power supply with diagrams and explanations. Shows how to solder and describes what to check and measure. Includes a basic guide to tracing the cause of a fault. It won't make you an expert but, if you are capable of soldering in components supplied as a kit, it will take you one step further so you understand why you are doing it and even help you figure out other possible fault causes and cures. If you buy a repair kit, you need this eBook. Click here

FREE - Beginners Guide to Electronics Easier to understand than anything you've read previously! Martin has a knack of explaining technical subjects in simple language. Components covered include resistors, diodes, transistors and capacitors. As an example, it describes in detail how to build a flashing LED circuit on perforated stripboard ("Veroboard") with a photograph of every stage. This is NOT just another boring technical eBook full of mathematical equations. You'll like it! Ideal for everyone from the young student to the retired lady looking for a new hobby. You'll definitely want more! Click here