spiney
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- My Satellite Setup
- Pace 2200 Sky digibox with ftv card, Comag SL65 FTA sat receiver, 40cm Sky minidish, Setpal terrestrial receiver (for free uk tv only!).
- My Location
- Midlands
a) This is finished version (in my opinion!).
Comments welcome, please add them below.
Admittedly, it's very longwinded and wordy (my "trademark"!), 'cos there's no similar guide on Internet (at least, I can't find one), so I've covered basic principles, and given examples of main system types. I'd rather annoy people by going O.T.T. than by being too cryptic.
c) Maybe this is unsuitable for forum? If so, fair enough. Anyway, others can now re-edit, completely ignore, trash it, or write something completely different, whatever.
d) There's similar stuff in books, standard work is Newnes Guide To Satellite TV, by Stevenson, often in public libraries, 4th edition or later.
e) Many thanks for info about satCR below, i'm not ignoring it, but most UK multiswitch installations are for Sky, and digiboxes won't have satCR for forseeable future. But, maybe somebody else could do that guide?
= = = = = = = = = == = == = = = = = = = = = = = = = = =.
**MULTISWITCH GUIDE**
MULTISWITCH INFO ON INTERNET
By far best source is Spaun catalogue, go www.spaun.de , click news, then just download it. Shows their complete multiswitch range, with lots of example diagrams. However, it's a 12MB pdf file, so you need wideband Internet connection, dialup modem will take at least 15 mins (and probably fail!).
Without wideband, there's still USA Spaun website www.spaun.com , which has "examples".
For comparative UK prices, different makes (but not Spaun), Farnell components, www.cpc.co.uk , search "multiswitch".
Spaun UK distributor is Teldis www.teldis.com .
Global product range - and sales - at www.globalcom.co.uk .
And there's www.jwhardy.co.uk , WiSi systems, many small pdf docs with very helpful diagrams.
Otherwise, just Google "multiswitch", but there's limited stuff there.
A "CAUTION" ABOUT LOWER COST MULTISWITCHES.
Some lower price multiswitches (mostly "standalone" types) have recently become available - from cpc and other retailers - which are "functionally equivalent" to more expensive types, but with worse performance specs, in particular a much lower terr-to-sat isolation (maybe 23 dB, instead of 35 or better). Such devices "work", but give far less protection from spurious modulation products, in situations where there might be wideband r.f. interference on terrestrial frequencies (characterised by "general noise" on am and fm radio, "patterning" on VHF/UHF tv channels, etc). If intending to also distribute terrestrial frequencies via a multiswitch - see below - then be aware of this before selecting a particular model.
(Very high level terr interference can "break through" into the satellite part of a multiswitch, maybe making some sat channels unreceivable, and in rare extremely bad cases cause the amplifiers to "saturate", ie output garbage. The higher the terr to sat isolation, the more protection you have from this!).
DISCLAIMER.
All the info below is believed correct, and given in good faith, but I'm not liable for any problems caused, make sure you know what you're doing, and check specs on particular equipment items.
LEGAL WARNING.
Multiswitches go into “public buildings” – flats, apartment blocks, also offices, factories, schools etc – so they’re subject to electrical wiring regulations. These depend on which country you’re in, check local ones. For multiswitches, such regulations mostly cover electrical safety earthing; minimum earth wire minimum diameter, allowed configurations, “acceptable” earth points, etc. There’s also other rules: building regulations, fire safety, local planning requirements, etc. These laws are there for peoples’ protection and safety, and breaking them can result in prosecution (lawsuits).
(In United Kingdom, relevant electrical laws include: IEE wiring regulations; EU Directives; CENLEC specifications. For rough UK only guidance, visit www.dtg.org.uk, see pdf documents on communal antenna systems).
Phew, now that’s out of the way ……..
GENERAL PRINCIPLES.
((added note: satellite i.f. distribution is "transparent" to the modulation type used. The distributed signals can be either digital standard definition (DVBS-1,MPEG2) or digital high definition (DVBS-1,MPEG2 "high profile" / DVBS-2,MPEG4), or various older analogue fm systems (inc. MAC, if any left!), or any mixture of these, it all depends on what the satellite transmits. The difference is in the sat receiver type you need to decode the signals!)).
1) Multiswitches allow you to connect many satellite receivers – possibly several hundred - to a single satellite dish (something that’s otherwise impossible!).
(the other rarely used method is “head-end distribution” - demodulating just a few sat channels, using individual sat receivers each “fixed” on 1 channel - then remodulating them as “pseudo-terrestrial” TV channels, which must carefully “fit between” the already existing local terrestrial TV channels, on cable distribution only. This limits you to just a few sat channels, maybe 30 max, and is horribly expensive, so it isn’t often done. But, it does avoid “end-point” satellite receivers altogether, since you receive the “converted” sat channels on “standard” UHF TV receivers, so it’s sometimes used in big hotels, office blocks, etc).
2) For terrestrial TV multi-distribution, you just point the aerial at the transmitter, run the coax cable to a distribution amplifier, then from this you can “feed” as many terr TV receivers as you want. Nice and simple!
3) But as readers know, satellite TV is more complicated! The satellite simultaneously broadcasts High and Low bands, with Vertical and Horizontal polarisations, giving 4 “polarities” (H/V, H/H, L/V, L/H). The coax cable connecting satellite receiver to lnb (satellite antenna) is bandwidth limited, and can only “carry” one polarity at any time. So, the lnb outputs only 1 of the 4 polarities, which one being decided by “control signals” (14/18v dc, 22Khz, Diseqc) from the receiver, sent back up the connecting cable to lnb.
4) This means that multiple satellite receivers can’t “share” one lnb, as their control signals would clash, and at any time the lnb outputs only one polarity (having, at most, only a quarter of the received channels).
5) The simplest way round this is to fit a multi-output lnb to the dish, where each different output “acts like” a separate lnb. Such lnbs are available with up to 24 outputs (I think!). But, you can’t go beyond that, and anyway it’s a lot of cables from one dish to individual receivers, and if the lnb goes faulty …..
6) So, the solution is “polarity trunking”; the 4 polarities must each go onto a separate cable (each polarity, by itself, occupies a 1Ghz bandwidth, 1-2 Ghz, just about what one coax will “carry”!). These 4 cables are then “bundled together”, and treated as a 4-in-1 “single trunk”, going to wherever the distribution is required.
You can have the 4 trunk cables in any configuration you want; single long run, star, tree, mixed, etc. But, each time there’s a split, it’s 4 cables so you need 4 splitters! And for signal boosting, you need 4 line amplifiers each time! So, it’s best to keep cabling as simple as possible, just one long run (if you can). Normally, you’d only do cable splitting where it’s really needed, in a very big building, maybe into a tree configuration if that’s necessary, for perhaps up to several hundred distribution “end-points” (where the individual sat receivers join on).
7) For the the lnb, you use a “Quattro” type. This has 4 fixed (non-switchable) polarity outputs, clearly marked, with a different polarity on each output, and you connect these outputs to the 4 trunk cables (once the specific polarity on each trunk cable is decided, don’t mix them up, otherwise some sat channels will “go missing”!).
(Don’t confuse “Quattro” with “quad universal switched”, a multi-output type lnb that just happens to have 4 outputs! Although, some multiswitches can use these instead of quattros, by sending the required control signals to the 4 switchable outputs, but quattros are cheaper so are normally used instead).
8) Usually, multiswitch systems also include terrestrial TV distribution. That way, you only have 1 “endpoint” coax cable into each separate flat (or room), instead of 2, which you’d need for completely separate sat and terr distribution systems. In which case, you then have 5 trunk cables, 4 sat trunks, each carrying 1-2 Ghz sat i.f. (intermediate frequency) - as above - and now also a 5th trunk carrying the terrestrial TV frequencies (UHF only in UK -maybe also VHF TV in some countries - and possibly also VHF band 2 fm radio and DAB radio, if you want these things!).
So, most of the available equipment is made for combined sat/terr distribution, and takes 5 trunk cables, and for satellite only you just omit the 5th (terrestrial) trunk, although some equipment is made for only satellite (therefore is slightly cheaper)!
(If combining several tv/fm/dab aerials - prior to multiswitch - then follow the same rules you would for such distribution systems, use correct aerials with proper combiners etc).
9) Endpoint cables. This all works out quite nicely, because sat i.f. is 1-2 Ghz, and terrestrial UHF TV “sits under” it at 450-890 Mhz. So, connected to the endpoint cable going into a flat, the satellite receiver simply selects which 1 of the 4 trunk “sat i.f.” signals it wants - to receive the required polarity - using the usual 14/18v/22kHz control signals (exactly as it would if connected directly to a standard lnb). There you go! Meanwhile, on the same end-cable, terr TV distribution is also present at lower frequencies. So, if you split the endpoint cable, then you can connect to a terrestrial TV receiver as well (ain’t it clever!).
(To a single endpoint cable, it should be clear that you can only connect up one satellite receiver at a time. After all, that was the original problem, it’s exactly why we need multiswitches in the first place! But, as in para 2 above, the terrestrial signal can be endlessly split, so you can connect as many terrestrial receivers as you like!).
(On a multiswitch system, if you want several sat receivers in one room, or Sky+ or similar, then you just use several additional endpoint connections. Which - once again - is pretty much the whole point!).
(i've said the trunks will "only carry" 1-2GHz, because of cable and amplifier limitations, but we break that rule for the final endpoint cables!).
10) Well, that’s the general principles covered! To recap, for sat multi-receiver distribution it’s necessary to feed the 4 polarities separately down 4 trunk cables. We’ve got a dish fitted with a Quattro lnb, the 4 trunks coming from it, and probably also a 5th terrestrial TV trunk. Basically, that’s it!
But, what powers the Quattro lnb? And more importantly, what sort of equipment lets endpoint sat receivers select a particular trunk (and also “mixes in” terrestrial)? Alright then, it’s time for some details ……….
PARTICULAR EQUIPMENT TYPES.
11) There’s 2 basic types of multiswitch equipment; “Cascade”, and, ahem, “Multiswitch”(!). Historically, cascade appeared first, uses separate components, and is most suitable for large to medium systems. Multiswitch came along later, puts “everything in one box”, and is better for medium to small systems. Both contain pretty much identical electronics, and you can “mix and match” from either, but let’s keep things simple for now.
(Different manufacturers’ systems also work pretty much the same, and in theory you can mix them up too, though I'm not recommending it!).
12 The best way to describe the 2 systems is by giving a particular example of each.
A CASCADE SYSTEM.
(Signal levels are given in the usual dB (decibel) notation, for gain/loss you just add/subtract, also some absolute levels given, for full explanation consult FAQs/ textbooks).
13) Imagine a “largish” building, a block of flats (apartment block), 15 floors high, 6 flats per floor (not “magic numbers”, it’s just to “build a mental picture”).
14) On roof goes the sat dish with Quattro lnb (normally getting Sky, if in UK, but of course might be any visible sat). And a TV aerial for terrestrial. If you also want FM, DAB, other stuff etc, these must all be “combined” - using amps and combiners - before the terrestrial trunk (as you would for a terrestrial only distribution system).
15) The 5 trunk cables are connected to lnb/aerial(s), then go through the roof and straight down the “riser” (building services shaft) to the bottom floor. Normally, the trunk cables would “lay flat” - side by side - all the way down, so you shouldn’t mix them up, but obviously it’s a good idea to ident them (with coloured PVC tapes or clips).
16) Now, just beneath the roof, we insert a Launch Amplifier into the trunks. There’s 5 trunk inputs on it, and also 5 trunk outputs, so you cut the trunk cables at that point and join them on (with f plugs), remembering to join the polarities to their corresponding correct inputs/outputs.
(I’ve said “run trunk cables straight down …”, and now I’ll keep saying “insert… (whatever-it-is!). In real life, you probably wouldn’t do that, instead you’d first put the equipment bits where needed, then cut cable sections to the required lengths).
17) The launch amplifier contains (and does):
a) a dc power supply (so you need mains power somewhere nearby!).
It feeds dc volts to the quattro lnb.
c) It contains 5 line amps, 1 for each trunk, each of approx 20 dB gain (that’s a lot, we’ll see why later). The amp gains are also “sloped”, rising at approx 6dB per octave, to counteract the cable’s high frequency attenuation, which approximates a 1-pole low pass filter).
d) It also feeds dc volts down one of the trunks (mainly for booster amps, though it can power other stuff as well, if necessary, sometimes that’s useful).
(“"Standard” launch amps allow you the option of using a quad lnb instead of Quattro, maybe also a C band one. A “budget” model won’t do that, and probably misses out the terrestrial line amp, won't have level adjustments, and generally has worse specs, see below).
18) Just below the launch amplifier (we’re still on top 15th floor), you put the first 6 output “multitap”. This has 5 trunk cable inputs and outputs, like the launch amp, so once again you cut the trunk cables to insert it. Then, the 6 outputs join onto the 6 end-cables into the individual flats on that floor.
19) The multitap accepts control signals from a sat receiver connected to an output (normally 22Khz/14/18v, but some are diseqc), and sends the appropriate sat polarity back down from that output (so, to sat receiver, it “looks like” an lnb). It also sends the entire terrestrial band - as above - regardless of sat polarity.
The multitap contains/does:
a) An “n” inputs x “m” outputs sat polarity switching matrix (probably pin diodes, though some use custom ICs).
Also a feedback network to enhance performance parameters (might be missing on budget models).
c) For terrestrial, it only “adds” the signal to each output, then isolates each output with a 20 dB signal attenuator for protection (exactly like a terr TV distribution amp does). That’s why the launch amp has a 20 dB gain.
(Multitaps are available with 2 to 10 outputs. For more than 10 flats on a single floor, you just insert more than 1 multitap!).
20) On next floor down (14th), you put a 2nd multitap.
21) On next floor down (13th), you put a 3rd multitap.
Each multitap has a “through-loss” (between inputs and outputs) of approximately 5 dB. So now, after passing through 3 multitaps, the trunk signals are about 15 dB lower, and should be boosted.
22) So on next floor down (12th), insert a Booster Amplifier.
(This again has 5 line amps, but usually lower gain, approx 15 dB, which gets levels to about back where we started. The booster amp doesn’t, have a power supply, instead it takes power from the trunk cable with dc volts on, supplied by launch amp).
23) Now, still on 12th floor, below booster amp, also insert a multitap (of course!).
24) 11th floor, insert multitap.
25) 10th floor, insert multitap.
26) 9th floor, insert booster amp, and below it insert multitap.
27) 8th, 7th, floors, insert multitaps.
28) 6th floor. Time for another booster amp. Or it should be. But, the launch amplifier will only “support” 2 subsequent booster amplifiers (usually, depends on manufacturer!). So, if the building has this many floors (which this one does), then insert another launch amplifier, requiring mains power. Then below it, obviously, another multitap.
(From it's inputs, the lauch amp supplies volts for an lnb, which we haven't got this time, so - strictly speaking - "dc blockers" should go into the 3 non-dc-feed trunks to stop this, but you can probably get away with omitting them!)
29) 5th floor, 4th floor, insert multitaps.
30) 3rd floor, booster amp, then multitap.
31) 2nd floor, 1st floor, multitaps.
32) This is the ground floor, the end of the “cascade”. So we add the final multitap (not bothering about a booster amp, at this point, so ground floor will just have an extra 5dB drop, not very important).
33) The final multitap – at bottom of cascade – still has 5 f socket outputs. We’re not going to connect up any more cables, but we must put five 75 Ohm “f” terminators into these sockets. Otherwise, analogue sat signals become “iffy” and digital ones unreceivable (transmission line theory, consult textbooks!).
34) …..and that’s a cascade system! As you can see, it contains many “bits and pieces”, requiring fixing stuff to walls, pulling through cables, fitting plugs to cables, etc, so installation can be fiddly and tedious.
35) As I’ve said, for even larger installations you may have to split the 5 trunks. For example, suppose the above building had 2 stairwells, with 6 flats per floor per stairwell. Then, you’d split the 5 trunks coming from the roof, and have 2 “cascade chains”, one going down each stairwell, For even bigger systems – approaching several hundred “endpoints” – you need to further split into a star or tree network. That’s a lot of installation (not really a one person job!).
A MULTISWITCH SYSTEM.
36) This is easier (you’ll be glad to hear!)
37) Imagine a different type of building, just 2 floors, with maybe 8 flats per floor (sometimes residential homes or “sheltered accommodation” is like this).
38) As before, on roof you put the sat dish with Quattro lnb and terrestrial aerial (obviously!).
39) The 5 trunks then go into a Cascade Multiswitch. This contains/does:
a) It has a dc power supply, requiring mains power nearby.
It feeds power to the lnb.
c) It has 5 trunk (lnb) inputs, and 5 trunk outputs.
d) It has 8 “endpoint” outputs, for cables to individual flats.
Usually, there’s little (or no) no “through loss”, so no booster amps are required after the trunk outputs.
(As before, more expensive models will allow multiple lnb types, probably include trunk signal level attenuators, and generally have better specs).
40) On bottom floor, feed the 5 trunk outputs from above “cascade” multiswitch into a "stand alone" multiswitch.
(this is identical, except it doesn’t have any trunk outputs, so obviously can only go on the end of any “cascade chain”. Or, you can still use a cascade type instead, but in that case must correctly terminate the 5 trunk outputs, as in the "cascade system" above).
41) "Stand Alone" Multiswitches (non-cascadable, so no trunk outputs!) are available with up to 16 outputs. Then, all you do is feed the 5 trunk cables in from roof, connect endpoint cables to individual outlets, and connect multiswitch to mains power. For a very small installation, that’s fairly easy!
MIX AND MATCH.
42) As you can see, both equipment types are similar (except multiswtiches are “all in one box”). So, you can use both together. For example, in "cascade system" above, instead of the 2nd launch amplifier further down, you could have a 6 output cascade multiswitch (which would supply further dc power for next booster amp, and also let you omit one multitap). Or, in the multiswitch system just above, you could replace the 2nd multiswitch with a multitap instead (remembering to terminate the outputs!), accepting the extra 5dB signal drop (not too important!).
However:
a) Each multiswitch requires mains power input to work. With cascaded multiswitches, each one must be separately powered.
Each amplifier adds further signal noise/distortion. For a long cascade, that’s why it’s better to use the cascade system, which keeps amplifier numbers down to a minimum.
RECEIVER POWERED MULTISWITCHES.
43) These are “stand alone” multiswitches, but powered by connected sat receivers, so they don’t need a mains power supply (can be useful). Obviously, if there’s not at least one sat receiver connected and switched on, then these stop working (so they don’t include terrestrial TV distribution!).
DUAL SATELLITE SYSTEMS.
44) These are available, in both standalone multiswitch and cascade forms. They have inputs for two Quattro lnbs, which means 9 trunk cables (4 polarities sat 1, 4 polarities sat 2, terrestrial), that’s a lot of wiring!
(To choose which satellite, connected receivers use lowest level diseqc (select lnb A or lnb. Receivers without this get only the “default” satellite).
MULTI SATELLITE SYSTEMS.
45) Spaun now do a cascade multiswitch system for (up to) 4 satellites + terrestrial (that's 17 trunk wires!). As above, connected sat receivers chose which satellite using Diseqc signalling.
(Also, Televes do an "infinitely expandable" multiswitch system; with sufficient trunk wiring you can multi-distribute as many satellites as you want, at least in principle. But doesn't Diseqc usually only allow selection of 4 lnbs?
see: http://www.televes.com/ingles/producto/ficha.asp?COD=296 .Or, www.televes.com - select your language - then go products, satellite tv, multiswitches).
LINK BUDGET AND ANALOGUE SAT.
46) In satellite books, there’s often a huge amount about “the link budget”. Basically, you’re supposed to work out the satellite field strength at reception point, know the dish and lnb gains, then work out signal strength at all points in the system! Not difficult, just look things up then add/subtract, but it’s tedious (though necessary for official contractors being paid to install!).
47) For digital only – most UK multiswitch installations just get Sky – some “rules of thumb” are generally adequate. Normally you use a dish “1 or 2 sizes larger than usual” (for Sky, instead of 43 cm, that’s 60 or 80 cm) for a “good signal” (probably about 90 dBuv). Then, just follow above rules, for cascade systems offset "through" signal loss with booster amplifiers, getting it roughly right (there's also "cable loss, but that's small, you can usually ignore it).
Multiswitch only systems aren’t usually big enough to worry about these losses.
Digital sat receivers will accept a very wide range of input levels, you can let signal strength drop quite a lot and still have a working system (I’m not recommending this (!), but certainly there’s lots of “leeway”).
48) But, many satellites still broadcast mixed analogue and digital signals, in which case the “link budget” is more important! Analogue receivers need 50-75dBuV – for “good” fm demodulation – which means an adequate lnb and dish to start with, and you can’t let the trunk signal levels drop too much!
(Also, it helps to use equipment with top specifications, especially on long cascades, as each booster amplifier adds slight distortion to the analogue fm signal.).
(And I've said nothing about cable losses, ignorable in smaller systems, but you'll have to take account of them in larger systems with longer cable runs. "Standard" sat coax is usually CT100 (or equivalent), losing 27dB/100m at 1.8Ghz. Using lower loss CT125 (or equivalent) is better for trunk feeds, although extra booster amplifiers instead would probably be cheaper).
FAULT FINDING.
49) During installation, it’s a good idea to “test as you go” (rather than completely install, switch on, then find it doesn’t work!). For cascade, once some parts are in place, you can “connect up from top down”, each time putting in a “temporary” system end, by briefly inserting the trunk terminators at that point. Connect a sat receiver, test all 4 polarities and terr, then you know it’s all ok “so far down” (no connection mistakes or wire whiskers!). It’s not necessary to test every floor, you can do every third one, then go back if necessary!
Cascaded multiswitches follow the same principle, they’re just smaller systems.
50) If a working system develops a fault, it’s fairly easy to find from the symptoms, should be obvious, but if necessary you can start disconnecting various bits to isolate and find fault.
(By far the most likely fault – as in much other equipment – is failure of a switched mode power supply, in launch amps and multiswitches. This is always a removable small PCB card. Some manufacturers sell spares – eg Spaun – so you can solder in a new one, but meanwhile the system’s broken, and in any case a new replacement multiswitch won’t cost much more, so best solution is just to replace it with a new one).
Otherwise, to fault trace, at any point you can disconnect a trunk feed, and connect a tv or sat receiver (or meter!) directly to it, that will show whether there's still a "working signal" on it.
51) For checking if a sat polarity is working, connect a trunk to a working sat receiver, then select a channel which should be on that polarity.
(Note that, for Sky receivers, a working high/vert polarity is essential, as this contains the channels frequencies info! Otherwise, the failure of any of the other (3) polarities will lose up to a quarter of Sky channels, but still leave Sky receivers "functioning").
52) For checking the 4 sat polarities, using just a Sky receiver, you can enter some individual channel details into "add channels". If you choose 4 different transponders, which broadcast on: hi/vert; hi/hor; lo/vert; lo/hor, then adding 1 (unencrypted!) tv channel from each will allow separate testing of each sat polarity, by checking you can receive a picture on it (regardless of whether or not hi/vert has failed, "disabling" all Sky receivers!).
(For directly checking the signal, instead, remember "signal test" shows only the default transponder, not the tv channel you're currently viewing! For that, instead of using "add channel", invoke the "installer menu" using remote: services, 4, 0, 1, select, then enter the particular transponder details into "maunal tune". This also allows checking the signal from any individual transponder, in case of problems receiving particular Sky channels).
(Note that current Astra2 transponder details are either on www.lyngsat.com, or www.satcodx.com , for 28 degrees East, of course!).
Note - sat Ku low band is up to 11.7 Ghz, above that frequency is high band!
This is "very fiddly", but does allow sat polarities checking with only a Sky receiver!
=== END-OF-DOCUMENT ===.
Comments welcome, please add them below.
Admittedly, it's very longwinded and wordy (my "trademark"!), 'cos there's no similar guide on Internet (at least, I can't find one), so I've covered basic principles, and given examples of main system types. I'd rather annoy people by going O.T.T. than by being too cryptic.c) Maybe this is unsuitable for forum? If so, fair enough. Anyway, others can now re-edit, completely ignore, trash it, or write something completely different, whatever.
d) There's similar stuff in books, standard work is Newnes Guide To Satellite TV, by Stevenson, often in public libraries, 4th edition or later.
e) Many thanks for info about satCR below, i'm not ignoring it, but most UK multiswitch installations are for Sky, and digiboxes won't have satCR for forseeable future. But, maybe somebody else could do that guide?
= = = = = = = = = == = == = = = = = = = = = = = = = = =.
**MULTISWITCH GUIDE**
MULTISWITCH INFO ON INTERNET
By far best source is Spaun catalogue, go www.spaun.de , click news, then just download it. Shows their complete multiswitch range, with lots of example diagrams. However, it's a 12MB pdf file, so you need wideband Internet connection, dialup modem will take at least 15 mins (and probably fail!).
Without wideband, there's still USA Spaun website www.spaun.com , which has "examples".
For comparative UK prices, different makes (but not Spaun), Farnell components, www.cpc.co.uk , search "multiswitch".
Spaun UK distributor is Teldis www.teldis.com .
Global product range - and sales - at www.globalcom.co.uk .
And there's www.jwhardy.co.uk , WiSi systems, many small pdf docs with very helpful diagrams.
Otherwise, just Google "multiswitch", but there's limited stuff there.
A "CAUTION" ABOUT LOWER COST MULTISWITCHES.
Some lower price multiswitches (mostly "standalone" types) have recently become available - from cpc and other retailers - which are "functionally equivalent" to more expensive types, but with worse performance specs, in particular a much lower terr-to-sat isolation (maybe 23 dB, instead of 35 or better). Such devices "work", but give far less protection from spurious modulation products, in situations where there might be wideband r.f. interference on terrestrial frequencies (characterised by "general noise" on am and fm radio, "patterning" on VHF/UHF tv channels, etc). If intending to also distribute terrestrial frequencies via a multiswitch - see below - then be aware of this before selecting a particular model.
(Very high level terr interference can "break through" into the satellite part of a multiswitch, maybe making some sat channels unreceivable, and in rare extremely bad cases cause the amplifiers to "saturate", ie output garbage. The higher the terr to sat isolation, the more protection you have from this!).
DISCLAIMER.
All the info below is believed correct, and given in good faith, but I'm not liable for any problems caused, make sure you know what you're doing, and check specs on particular equipment items.
LEGAL WARNING.
Multiswitches go into “public buildings” – flats, apartment blocks, also offices, factories, schools etc – so they’re subject to electrical wiring regulations. These depend on which country you’re in, check local ones. For multiswitches, such regulations mostly cover electrical safety earthing; minimum earth wire minimum diameter, allowed configurations, “acceptable” earth points, etc. There’s also other rules: building regulations, fire safety, local planning requirements, etc. These laws are there for peoples’ protection and safety, and breaking them can result in prosecution (lawsuits).
(In United Kingdom, relevant electrical laws include: IEE wiring regulations; EU Directives; CENLEC specifications. For rough UK only guidance, visit www.dtg.org.uk, see pdf documents on communal antenna systems).
Phew, now that’s out of the way ……..
GENERAL PRINCIPLES.
((added note: satellite i.f. distribution is "transparent" to the modulation type used. The distributed signals can be either digital standard definition (DVBS-1,MPEG2) or digital high definition (DVBS-1,MPEG2 "high profile" / DVBS-2,MPEG4), or various older analogue fm systems (inc. MAC, if any left!), or any mixture of these, it all depends on what the satellite transmits. The difference is in the sat receiver type you need to decode the signals!)).
1) Multiswitches allow you to connect many satellite receivers – possibly several hundred - to a single satellite dish (something that’s otherwise impossible!).
(the other rarely used method is “head-end distribution” - demodulating just a few sat channels, using individual sat receivers each “fixed” on 1 channel - then remodulating them as “pseudo-terrestrial” TV channels, which must carefully “fit between” the already existing local terrestrial TV channels, on cable distribution only. This limits you to just a few sat channels, maybe 30 max, and is horribly expensive, so it isn’t often done. But, it does avoid “end-point” satellite receivers altogether, since you receive the “converted” sat channels on “standard” UHF TV receivers, so it’s sometimes used in big hotels, office blocks, etc).
2) For terrestrial TV multi-distribution, you just point the aerial at the transmitter, run the coax cable to a distribution amplifier, then from this you can “feed” as many terr TV receivers as you want. Nice and simple!
3) But as readers know, satellite TV is more complicated! The satellite simultaneously broadcasts High and Low bands, with Vertical and Horizontal polarisations, giving 4 “polarities” (H/V, H/H, L/V, L/H). The coax cable connecting satellite receiver to lnb (satellite antenna) is bandwidth limited, and can only “carry” one polarity at any time. So, the lnb outputs only 1 of the 4 polarities, which one being decided by “control signals” (14/18v dc, 22Khz, Diseqc) from the receiver, sent back up the connecting cable to lnb.
4) This means that multiple satellite receivers can’t “share” one lnb, as their control signals would clash, and at any time the lnb outputs only one polarity (having, at most, only a quarter of the received channels).
5) The simplest way round this is to fit a multi-output lnb to the dish, where each different output “acts like” a separate lnb. Such lnbs are available with up to 24 outputs (I think!). But, you can’t go beyond that, and anyway it’s a lot of cables from one dish to individual receivers, and if the lnb goes faulty …..
6) So, the solution is “polarity trunking”; the 4 polarities must each go onto a separate cable (each polarity, by itself, occupies a 1Ghz bandwidth, 1-2 Ghz, just about what one coax will “carry”!). These 4 cables are then “bundled together”, and treated as a 4-in-1 “single trunk”, going to wherever the distribution is required.
You can have the 4 trunk cables in any configuration you want; single long run, star, tree, mixed, etc. But, each time there’s a split, it’s 4 cables so you need 4 splitters! And for signal boosting, you need 4 line amplifiers each time! So, it’s best to keep cabling as simple as possible, just one long run (if you can). Normally, you’d only do cable splitting where it’s really needed, in a very big building, maybe into a tree configuration if that’s necessary, for perhaps up to several hundred distribution “end-points” (where the individual sat receivers join on).
7) For the the lnb, you use a “Quattro” type. This has 4 fixed (non-switchable) polarity outputs, clearly marked, with a different polarity on each output, and you connect these outputs to the 4 trunk cables (once the specific polarity on each trunk cable is decided, don’t mix them up, otherwise some sat channels will “go missing”!).
(Don’t confuse “Quattro” with “quad universal switched”, a multi-output type lnb that just happens to have 4 outputs! Although, some multiswitches can use these instead of quattros, by sending the required control signals to the 4 switchable outputs, but quattros are cheaper so are normally used instead).
8) Usually, multiswitch systems also include terrestrial TV distribution. That way, you only have 1 “endpoint” coax cable into each separate flat (or room), instead of 2, which you’d need for completely separate sat and terr distribution systems. In which case, you then have 5 trunk cables, 4 sat trunks, each carrying 1-2 Ghz sat i.f. (intermediate frequency) - as above - and now also a 5th trunk carrying the terrestrial TV frequencies (UHF only in UK -maybe also VHF TV in some countries - and possibly also VHF band 2 fm radio and
DAB radio, if you want these things!).So, most of the available equipment is made for combined sat/terr distribution, and takes 5 trunk cables, and for satellite only you just omit the 5th (terrestrial) trunk, although some equipment is made for only satellite (therefore is slightly cheaper)!
(If combining several tv/fm/dab aerials - prior to multiswitch - then follow the same rules you would for such distribution systems, use correct aerials with proper combiners etc).
9) Endpoint cables. This all works out quite nicely, because sat i.f. is 1-2 Ghz, and terrestrial UHF TV “sits under” it at 450-890 Mhz. So, connected to the endpoint cable going into a flat, the satellite receiver simply selects which 1 of the 4 trunk “sat i.f.” signals it wants - to receive the required polarity - using the usual 14/18v/22kHz control signals (exactly as it would if connected directly to a standard lnb). There you go! Meanwhile, on the same end-cable, terr TV distribution is also present at lower frequencies. So, if you split the endpoint cable, then you can connect to a terrestrial TV receiver as well (ain’t it clever!).
(To a single endpoint cable, it should be clear that you can only connect up one satellite receiver at a time. After all, that was the original problem, it’s exactly why we need multiswitches in the first place! But, as in para 2 above, the terrestrial signal can be endlessly split, so you can connect as many terrestrial receivers as you like!).
(On a multiswitch system, if you want several sat receivers in one room, or Sky+ or similar, then you just use several additional endpoint connections. Which - once again - is pretty much the whole point!).
(i've said the trunks will "only carry" 1-2GHz, because of cable and amplifier limitations, but we break that rule for the final endpoint cables!).
10) Well, that’s the general principles covered! To recap, for sat multi-receiver distribution it’s necessary to feed the 4 polarities separately down 4 trunk cables. We’ve got a dish fitted with a Quattro lnb, the 4 trunks coming from it, and probably also a 5th terrestrial TV trunk. Basically, that’s it!
But, what powers the Quattro lnb? And more importantly, what sort of equipment lets endpoint sat receivers select a particular trunk (and also “mixes in” terrestrial)? Alright then, it’s time for some details ……….
PARTICULAR EQUIPMENT TYPES.
11) There’s 2 basic types of multiswitch equipment; “Cascade”, and, ahem, “Multiswitch”(!). Historically, cascade appeared first, uses separate components, and is most suitable for large to medium systems. Multiswitch came along later, puts “everything in one box”, and is better for medium to small systems. Both contain pretty much identical electronics, and you can “mix and match” from either, but let’s keep things simple for now.
(Different manufacturers’ systems also work pretty much the same, and in theory you can mix them up too, though I'm not recommending it!).
12 The best way to describe the 2 systems is by giving a particular example of each.
A CASCADE SYSTEM.
(Signal levels are given in the usual dB (decibel) notation, for gain/loss you just add/subtract, also some absolute levels given, for full explanation consult FAQs/ textbooks).
13) Imagine a “largish” building, a block of flats (apartment block), 15 floors high, 6 flats per floor (not “magic numbers”, it’s just to “build a mental picture”).
14) On roof goes the sat dish with Quattro lnb (normally getting Sky, if in UK, but of course might be any visible sat). And a TV aerial for terrestrial. If you also want FM, DAB, other stuff etc, these must all be “combined” - using amps and combiners - before the terrestrial trunk (as you would for a terrestrial only distribution system).
15) The 5 trunk cables are connected to lnb/aerial(s), then go through the roof and straight down the “riser” (building services shaft) to the bottom floor. Normally, the trunk cables would “lay flat” - side by side - all the way down, so you shouldn’t mix them up, but obviously it’s a good idea to ident them (with coloured PVC tapes or clips).
16) Now, just beneath the roof, we insert a Launch Amplifier into the trunks. There’s 5 trunk inputs on it, and also 5 trunk outputs, so you cut the trunk cables at that point and join them on (with f plugs), remembering to join the polarities to their corresponding correct inputs/outputs.
(I’ve said “run trunk cables straight down …”, and now I’ll keep saying “insert… (whatever-it-is!). In real life, you probably wouldn’t do that, instead you’d first put the equipment bits where needed, then cut cable sections to the required lengths).
17) The launch amplifier contains (and does):
a) a dc power supply (so you need mains power somewhere nearby!).
It feeds dc volts to the quattro lnb.c) It contains 5 line amps, 1 for each trunk, each of approx 20 dB gain (that’s a lot, we’ll see why later). The amp gains are also “sloped”, rising at approx 6dB per octave, to counteract the cable’s high frequency attenuation, which approximates a 1-pole low pass filter).
d) It also feeds dc volts down one of the trunks (mainly for booster amps, though it can power other stuff as well, if necessary, sometimes that’s useful).
(“"Standard” launch amps allow you the option of using a quad lnb instead of Quattro, maybe also a C band one. A “budget” model won’t do that, and probably misses out the terrestrial line amp, won't have level adjustments, and generally has worse specs, see below).
18) Just below the launch amplifier (we’re still on top 15th floor), you put the first 6 output “multitap”. This has 5 trunk cable inputs and outputs, like the launch amp, so once again you cut the trunk cables to insert it. Then, the 6 outputs join onto the 6 end-cables into the individual flats on that floor.
19) The multitap accepts control signals from a sat receiver connected to an output (normally 22Khz/14/18v, but some are diseqc), and sends the appropriate sat polarity back down from that output (so, to sat receiver, it “looks like” an lnb). It also sends the entire terrestrial band - as above - regardless of sat polarity.
The multitap contains/does:
a) An “n” inputs x “m” outputs sat polarity switching matrix (probably pin diodes, though some use custom ICs).
Also a feedback network to enhance performance parameters (might be missing on budget models). c) For terrestrial, it only “adds” the signal to each output, then isolates each output with a 20 dB signal attenuator for protection (exactly like a terr TV distribution amp does). That’s why the launch amp has a 20 dB gain.
(Multitaps are available with 2 to 10 outputs. For more than 10 flats on a single floor, you just insert more than 1 multitap!).
20) On next floor down (14th), you put a 2nd multitap.
21) On next floor down (13th), you put a 3rd multitap.
Each multitap has a “through-loss” (between inputs and outputs) of approximately 5 dB. So now, after passing through 3 multitaps, the trunk signals are about 15 dB lower, and should be boosted.
22) So on next floor down (12th), insert a Booster Amplifier.
(This again has 5 line amps, but usually lower gain, approx 15 dB, which gets levels to about back where we started. The booster amp doesn’t, have a power supply, instead it takes power from the trunk cable with dc volts on, supplied by launch amp).
23) Now, still on 12th floor, below booster amp, also insert a multitap (of course!).
24) 11th floor, insert multitap.
25) 10th floor, insert multitap.
26) 9th floor, insert booster amp, and below it insert multitap.
27) 8th, 7th, floors, insert multitaps.
28) 6th floor. Time for another booster amp. Or it should be. But, the launch amplifier will only “support” 2 subsequent booster amplifiers (usually, depends on manufacturer!). So, if the building has this many floors (which this one does), then insert another launch amplifier, requiring mains power. Then below it, obviously, another multitap.
(From it's inputs, the lauch amp supplies volts for an lnb, which we haven't got this time, so - strictly speaking - "dc blockers" should go into the 3 non-dc-feed trunks to stop this, but you can probably get away with omitting them!)
29) 5th floor, 4th floor, insert multitaps.
30) 3rd floor, booster amp, then multitap.
31) 2nd floor, 1st floor, multitaps.
32) This is the ground floor, the end of the “cascade”. So we add the final multitap (not bothering about a booster amp, at this point, so ground floor will just have an extra 5dB drop, not very important).
33) The final multitap – at bottom of cascade – still has 5 f socket outputs. We’re not going to connect up any more cables, but we must put five 75 Ohm “f” terminators into these sockets. Otherwise, analogue sat signals become “iffy” and digital ones unreceivable (transmission line theory, consult textbooks!).
34) …..and that’s a cascade system! As you can see, it contains many “bits and pieces”, requiring fixing stuff to walls, pulling through cables, fitting plugs to cables, etc, so installation can be fiddly and tedious.
35) As I’ve said, for even larger installations you may have to split the 5 trunks. For example, suppose the above building had 2 stairwells, with 6 flats per floor per stairwell. Then, you’d split the 5 trunks coming from the roof, and have 2 “cascade chains”, one going down each stairwell, For even bigger systems – approaching several hundred “endpoints” – you need to further split into a star or tree network. That’s a lot of installation (not really a one person job!).
A MULTISWITCH SYSTEM.
36) This is easier (you’ll be glad to hear!)
37) Imagine a different type of building, just 2 floors, with maybe 8 flats per floor (sometimes residential homes or “sheltered accommodation” is like this).
38) As before, on roof you put the sat dish with Quattro lnb and terrestrial aerial (obviously!).
39) The 5 trunks then go into a Cascade Multiswitch. This contains/does:
a) It has a dc power supply, requiring mains power nearby.
It feeds power to the lnb.c) It has 5 trunk (lnb) inputs, and 5 trunk outputs.
d) It has 8 “endpoint” outputs, for cables to individual flats.
Usually, there’s little (or no) no “through loss”, so no booster amps are required after the trunk outputs.
(As before, more expensive models will allow multiple lnb types, probably include trunk signal level attenuators, and generally have better specs).
40) On bottom floor, feed the 5 trunk outputs from above “cascade” multiswitch into a "stand alone" multiswitch.
(this is identical, except it doesn’t have any trunk outputs, so obviously can only go on the end of any “cascade chain”. Or, you can still use a cascade type instead, but in that case must correctly terminate the 5 trunk outputs, as in the "cascade system" above).
41) "Stand Alone" Multiswitches (non-cascadable, so no trunk outputs!) are available with up to 16 outputs. Then, all you do is feed the 5 trunk cables in from roof, connect endpoint cables to individual outlets, and connect multiswitch to mains power. For a very small installation, that’s fairly easy!
MIX AND MATCH.
42) As you can see, both equipment types are similar (except multiswtiches are “all in one box”). So, you can use both together. For example, in "cascade system" above, instead of the 2nd launch amplifier further down, you could have a 6 output cascade multiswitch (which would supply further dc power for next booster amp, and also let you omit one multitap). Or, in the multiswitch system just above, you could replace the 2nd multiswitch with a multitap instead (remembering to terminate the outputs!), accepting the extra 5dB signal drop (not too important!).
However:
a) Each multiswitch requires mains power input to work. With cascaded multiswitches, each one must be separately powered.
Each amplifier adds further signal noise/distortion. For a long cascade, that’s why it’s better to use the cascade system, which keeps amplifier numbers down to a minimum.RECEIVER POWERED MULTISWITCHES.
43) These are “stand alone” multiswitches, but powered by connected sat receivers, so they don’t need a mains power supply (can be useful). Obviously, if there’s not at least one sat receiver connected and switched on, then these stop working (so they don’t include terrestrial TV distribution!).
DUAL SATELLITE SYSTEMS.
44) These are available, in both standalone multiswitch and cascade forms. They have inputs for two Quattro lnbs, which means 9 trunk cables (4 polarities sat 1, 4 polarities sat 2, terrestrial), that’s a lot of wiring!
(To choose which satellite, connected receivers use lowest level diseqc (select lnb A or lnb
. Receivers without this get only the “default” satellite).MULTI SATELLITE SYSTEMS.
45) Spaun now do a cascade multiswitch system for (up to) 4 satellites + terrestrial (that's 17 trunk wires!). As above, connected sat receivers chose which satellite using Diseqc signalling.
(Also, Televes do an "infinitely expandable" multiswitch system; with sufficient trunk wiring you can multi-distribute as many satellites as you want, at least in principle. But doesn't Diseqc usually only allow selection of 4 lnbs?
see: http://www.televes.com/ingles/producto/ficha.asp?COD=296 .Or, www.televes.com - select your language - then go products, satellite tv, multiswitches).
LINK BUDGET AND ANALOGUE SAT.
46) In satellite books, there’s often a huge amount about “the link budget”. Basically, you’re supposed to work out the satellite field strength at reception point, know the dish and lnb gains, then work out signal strength at all points in the system! Not difficult, just look things up then add/subtract, but it’s tedious (though necessary for official contractors being paid to install!).
47) For digital only – most UK multiswitch installations just get Sky – some “rules of thumb” are generally adequate. Normally you use a dish “1 or 2 sizes larger than usual” (for Sky, instead of 43 cm, that’s 60 or 80 cm) for a “good signal” (probably about 90 dBuv). Then, just follow above rules, for cascade systems offset "through" signal loss with booster amplifiers, getting it roughly right (there's also "cable loss, but that's small, you can usually ignore it).
Multiswitch only systems aren’t usually big enough to worry about these losses.
Digital sat receivers will accept a very wide range of input levels, you can let signal strength drop quite a lot and still have a working system (I’m not recommending this (!), but certainly there’s lots of “leeway”).
48) But, many satellites still broadcast mixed analogue and digital signals, in which case the “link budget” is more important! Analogue receivers need 50-75dBuV – for “good” fm demodulation – which means an adequate lnb and dish to start with, and you can’t let the trunk signal levels drop too much!
(Also, it helps to use equipment with top specifications, especially on long cascades, as each booster amplifier adds slight distortion to the analogue fm signal.).
(And I've said nothing about cable losses, ignorable in smaller systems, but you'll have to take account of them in larger systems with longer cable runs. "Standard" sat coax is usually CT100 (or equivalent), losing 27dB/100m at 1.8Ghz. Using lower loss CT125 (or equivalent) is better for trunk feeds, although extra booster amplifiers instead would probably be cheaper).
FAULT FINDING.
49) During installation, it’s a good idea to “test as you go” (rather than completely install, switch on, then find it doesn’t work!). For cascade, once some parts are in place, you can “connect up from top down”, each time putting in a “temporary” system end, by briefly inserting the trunk terminators at that point. Connect a sat receiver, test all 4 polarities and terr, then you know it’s all ok “so far down” (no connection mistakes or wire whiskers!). It’s not necessary to test every floor, you can do every third one, then go back if necessary!
Cascaded multiswitches follow the same principle, they’re just smaller systems.
50) If a working system develops a fault, it’s fairly easy to find from the symptoms, should be obvious, but if necessary you can start disconnecting various bits to isolate and find fault.
(By far the most likely fault – as in much other equipment – is failure of a switched mode power supply, in launch amps and multiswitches. This is always a removable small PCB card. Some manufacturers sell spares – eg Spaun – so you can solder in a new one, but meanwhile the system’s broken, and in any case a new replacement multiswitch won’t cost much more, so best solution is just to replace it with a new one).
Otherwise, to fault trace, at any point you can disconnect a trunk feed, and connect a tv or sat receiver (or meter!) directly to it, that will show whether there's still a "working signal" on it.
51) For checking if a sat polarity is working, connect a trunk to a working sat receiver, then select a channel which should be on that polarity.
(Note that, for Sky receivers, a working high/vert polarity is essential, as this contains the channels frequencies info! Otherwise, the failure of any of the other (3) polarities will lose up to a quarter of Sky channels, but still leave Sky receivers "functioning").
52) For checking the 4 sat polarities, using just a Sky receiver, you can enter some individual channel details into "add channels". If you choose 4 different transponders, which broadcast on: hi/vert; hi/hor; lo/vert; lo/hor, then adding 1 (unencrypted!) tv channel from each will allow separate testing of each sat polarity, by checking you can receive a picture on it (regardless of whether or not hi/vert has failed, "disabling" all Sky receivers!).
(For directly checking the signal, instead, remember "signal test" shows only the default transponder, not the tv channel you're currently viewing! For that, instead of using "add channel", invoke the "installer menu" using remote: services, 4, 0, 1, select, then enter the particular transponder details into "maunal tune". This also allows checking the signal from any individual transponder, in case of problems receiving particular Sky channels).
(Note that current Astra2 transponder details are either on www.lyngsat.com, or www.satcodx.com , for 28 degrees East, of course!).
Note - sat Ku low band is up to 11.7 Ghz, above that frequency is high band!
This is "very fiddly", but does allow sat polarities checking with only a Sky receiver!
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