Satellite and Appendix
Where I put stuff when I can`t think of anywhere else to put it, though to be frank, there`s some pretty useful (and interesting) stuff on here, even though I say so myself…..
In the UK television transmissions are usually referred to by a channel number (not to be confused with programme channel, e.g. BBC1) as opposed to a frequency. Both the channel number and the frequency are given on all our Channel Allocation Guides (e.g. the one for Crystal Palace) , plus the table below also shows channel number v frequency (and also the wavelengths).
In the case of analogue the channel number is/was related to the frequency thus :
Fv = 8n + 303.25
Where Fv = Frequency of the vision carrier in MHz and n = Channel Number.
Note analogue does still exist for modulated RF signal distribution !
For digital the channel number is related to the frequency thus :
Fc = 8n + 306
Where Fc = Centre frequency of the MUX, and n = Channel Number.
As an approximation, good enough for most tuners, the analogue frequencies are 3MHz
lower than the analogue (although it`s actually 306 -
Since most tuners use channel numbers this 3MHz difference is not usually significant, but if you are trying to enter the actual frequency to yours it obviously might be for you !
Some digital MUXES are transmitted with a channel offset and these are + or -
These offset frequencies can be found in the relevant Ofcom document.
The vast majority of digital TVs or STBs can still tune in to a MUX even if it has an offset and this is also the case in manual tuning. But you have trouble trying to tune in your MUXES its always worth checking that the tuner is not being sidelined by an offset, though this should be very rare.
6 Finally install the pole on the bracket. The aerial and cable would usually be pre installed on
the pole at this point. If it`s a cranked pole ensure the aerial is pointing in approximately the right direction relative to the crank and the transmitter.
1 & 2 [as an alternative] In order to temporarily loop the lash around the chimney (before adding the bracket) pass the wire round the stack then lightly bend the free end of the lash wire so it can pass through the Eye bolt. With the lash wire already looped around the stack now place the chimney bracket on the corner of the chimney, install the Eye bolt and the J bolt in the relevant holes on the bracket then attach the wire to the J bolt as described above (at 3 above).
Do not install a chimney bracket on the top two or three courses of bricks.
Never fit a wall bracket on a chimney, unless it`s a big stack and a small aerial on a short pole.
If the chimney is ever used, or likely to be used, install the aerial on the upwind side of the
stack preferably with a cranked pole. If possible fit an end mounting aerial (e.g. a Log36) on correct side of the stack to "see" the transmitter using a short pole so the antenna is below the chimney pot. This is to avoid smoke damage to the aerial.
1 Install the J bolt and the Eye bolt (c/w its attached lashing wire) in the relevant holes of the chimney bracket. It is very important to ensure the nuts are unscrewed as far as possible so as to give maximum chance that the lash will tighten up at stage 5. [Also see 1 & 2 below]
2 Hold the bracket on the corner of the chimney and pass the lash wire (which is attached to the Eye bolt) round the chimney. Straighten the wire out and and slightly "curve" it, then pass the wire over the top of the chimney, or around it, if necessary by throwing the end round and catching it.
Ensure the lash wire is horizontal all the way round the chimney.
3 Loop the free end of the wire round the J bolt and pull as tight as possible, then wrap the wire round the J bolt twice. Finally wrap the wire about six times tightly back round the lash wire itself.
Now [and only now....] cut off the lash wire.
Two 6x6 chimney brackets used for one pole. This is perfectly acceptable, and
Is actually stronger than using one larger bracket.
Note the top lash is hand twisted and the bottom
one is pre terminated.
Also note that the bottom bracket is galvanised and the top one only painted.
Health & Safety Disclaimer :
Gravity plus height is a bad combination, don`t fall off the roof.
If in any doubt about this scientific fact, don`t do the job.
This is not meant to be an exhaustive article on the use of ladders, it`s just a reminder of the most important things to remember when using one.
Surface : The ground on which the ladder is to be rested should be firm, and not slippery.
I`d have thought both of these went without saying, but then again.........
Level the ladder : Use of a ladder leveller is the best idea, but not everyone has one of those. Never use wooden wedges or a stone. Use a large piece of plywood (neither painted nor wet) under the ladder leg with the gap under it. Chock the board so it levels the ladder but, just as importantly, it`s stable and isn`t going to go anywhere.
Angle of the ladder : This should be about 70 degrees from the horizontal, a more practical check is the 4 up 1 out rule, e.g. if the top of the ladder is 8m from the ground, the base should be 2m out from the wall. Some ladders have a "ladder line" at the correct angle painted on the side.
Mitre chimney bracket installed round a chimney. This isn`t one of ours, you can tell that because of the rust staining on it, which there wouldn`t be on one we sold, not for 20 or 30 years anyway !
For the above system we would recommend our variable gain mast head amp, in order to obtain the correct signal level. Ideally a meter should be used, and not a £30 job, even the (not entirely believable) signal levels on STBs/TVs are better than those. But at the end of the day what actually counts is how often the picture/sound breaks up, and the best signal level can usually be obtained by trial and error with the variable gain setting.
Side output of tap = -
Through output of tap = -
(e.g. last -
If the mast head amp were at maximum gain, then then add 22dB to all the above readings to get the figures relative to the signal at the aerial.
For the above system we would recommend our variable gain power amp, in order to obtain the correct signal level. Ideally a meter should be used, and not a £30 job, even the (not entirely believable) signal levels on STBs/TVs are better than those. But at the end of the day what actually counts is how often the picture/sound breaks up, and the best signal level can often be obtained by trial and error with the variable gain setting(s).
Assuming a 1dB cable loss (equating to about 10m) between each tap, and a 2dB cable loss [about 20m] between the taps and 2 way splitters, sample estimated loss figures at various points on the system (all relative to those at the input to the first tap) would be as follows :
Input to first 2 way splitter = -
Input to second 2 way splitter = -
Input to third 2 way splitter = -
Input to fourth 2 way splitter = -
(e.g. the -
1 x 2dB cable loss + 1 x 4dB 2way splitter loss + 1 x 12dB 8 way splitter loss)
A 3dB difference in final outputs would not usually be significant.
It will be noted that there is a 15dB attenuator before the last set of splitters (to equalise the output levels, thus it would be possible, if required, to add more splitters and therefore extra outputs. If the power amp were at maximum gain, then add 35dB to all the above readings to get the figures relative to the signal at the aerial. If the pre amp was used with the power amp then the total would be 44dB. Thus even the most attenuated outputs in the above system would receive only 3dB less than the aerial is providing, or, if a pre amp is used, 6dB more.
Tie the ladder off : Tying a ladder off is time consuming, and, to be honest, most people don`t bother. But it could save your life, or at least ensure you don`t end up playing wheelchair basketball...... If it`s done properly it not only makes using a ladder far safer, but it will give you much more confidence in its use. Instead of flexing and wobbling as you climb it the ladder will stay rock steady, like going up stairs, literally, try it and you`ll see what I mean. And if you do over balance you can grab the ladder, and you won`t experience that sickening feeling as it starts sliding......
The best way to tie off a ladder is with one of those small ratchet straps used for securing luggage or similar, but if you haven`t got one of those anything which is reasonably strong (and capable of getting a fair bit of tension on the tie off) is better than nothing If there`s nothing convenient to tie off to then screw an eye screw / eyebolt into the wall. It`ll only leave a small hole when you remove it and you may, at some time in the future, want to use it again anyway. Loop the strap round a rung about half way up, then angle it downwards about 45 degrees or so because you don`t want to just drag the bottom of the ladder in towards the wall. Don`t put too much force on the strap because that`ll just damage the ladder. All you want to do is take up any play in the ladder and ensure it doesn`t move.
If using a ladder in conjunction with a roof ladder always lash the two together at the point they meet at the edge of the roof. Apart from ensuring the ladder doesn`t fall (and leave you embarrassingly stranded up on the roof ! ) if you do fall down the roof you have at least got something to grab onto [i.e. the top of the ladder] which isn`t going to move.
Don`t over reach : Saying don`t reach out to the side when using a ladder is obvious, but also pretty stupid, because for most jobs you have to. The thing is don`t reach out too far, particularly if the ladder isn`t tied off, which is another reason for tying it off in the first place.
Top of the ladder : This should be above the top of the wall, by a couple or three feet, this gives you something to hold onto as you climb onto the roof (or whatever), and also something to grab onto if you fall off the roof, so long as it`s tied off, obviously.
To be honest it`s very rare for aerial installers to ever fall off the roof, though it`s not unknown.
Just so long as you`re careful it`s pretty safe fitting the odd aerial.
Compare it to driving (over the years you do it), now that is dangerous......
I am not expert in electrical or building regulations, but the last I heard the definition of "a system", under which additional safety regulations are applicable, is one which supplies points to rooms behind more than one lockable door. That is to say if all points are behind one lockable door it is classed as domestic, for which no regulations apply for TV distribution systems for earth bonding requirements, as far as I`m aware.
The most important requirement for system work is that it must be electrically bonded to the building`s main earth terminal (see linked pdf). All our splitters (except the CoAx one), taps and mains amps (except the 2 way amp) have earth bonding terminals and these should be used to connect onto said earth terminal. The connection can be made anywhere on the system, or at more than one point. Incidentally, use of copper/copper satellite cable (as opposed to RG6 type) is preferable for earth bonded systems because, in a fault situation (admittedly a highly unlikely occurence.....) it`s capable of carrying greater current down to earth and blowing the mains supply safety device [either a fuse or a circuit breaker].
Those considering installing a system (under the definition of a system above) are advised to read the appropriate electrical code of practice.
As a bit of controversial food for thought. I have to say that speaking as a TV engineer (or more accurately an ex TV engineer) I cannot actually imagine how a TV, or an aerial amp come to that, could actually put dangerous voltages out of the aerial socket(s). In fact in August 2011 I phoned round 7 of our best (ex) customers [we supplied TV service manuals up to July 2010] and none of them had ever seen such a fault condition. The only possible method would be some ignoramus who knows nothing about TVs trying to mend it, and even then it`d probably blow the power supply, or just lie there dead (the TV that is). But if, by some incredible set of circumstances, a particular piece of equipment managed to develop a fault which could put mains voltage onto said socket (and I`ve never seen it in 15 years) I`d have thought it`d be far more likely it`d blow the fuse(s) or even blow out a PCB track.
And anyway years spent delving into the depths of TVs whilst they`re switched on means I`ve had dozens of mains shocks * (though it`s advisable not to be touching anything earthed whilst this happens though ! ). What can I say ? I`m still here.
But on the other hand people do get hit by asteroids, apparently.
Whatever the likelihood of any problem, remember the golden rule : cover your arse.
* Interesting sidelight. Most people think that getting the odd shock is a TV engineer`s biggest bugbear, whereas in actual fact the most painful part of being a TV engineer is getting accidental burns off the solder or the soldering iron !
And they can hurt for days, not just a few seconds as the average electric shock does.
We are more than willing to give advice to those actually purchasing from us. Could those only seeking information please just find the answer somewhere on this site, or ring an aerial installer local to them, or call the reception advice phone numbers.
Further comment on regulations came from Mike Felton who, after reading our tests on interference problems running CoAx next to mains cable, took the trouble to inform us that it`s against Electrical Regulations to run 2 different categories of cable together unless separated by a fireproof barrier. We`re grateful to him for taking the time to contact us.
We`ve been told now, and, although I`m no electrician, it does actually sound like the kind of thing you`d find in the Electrical Regulations. However, just like the above example where in reality it`d be virtually impossible to get a mains shock from the tuner of a TV, I have to say I cannot personally think of any realistic combination of circumstances were there`d be any significant danger from running mains cable next to CoAx. Certainly not from the electric shock point of view anyway, the current would have to get through not one, not two, but three layers of insulation ! If one or other of the cables was to catch fire that would be a different kettle of fish risk wise, but if, say, the mains cable caught fire, I`d have thought any proximity it may have to a TV lead would be the least of your worries.........
That said, particularly if you`re not doing the job in your own home, cover your arse.
If you`ve found this site informative and, hopefully, interesting as well,
Well that really is a question.
Firstly not all aerials read short circuit across the input, half an hour with a meter on a load of aerials round our shop produced the results shown in the table.
But why do any aerials read short ?
Well that`s the wrong question in a way because the dipole(s) are just "generating" the tiny current induced by the signal. Whether the dipole(s) is short circuit or open circuit is actually irrelevant, all that counts is that the dipole(s) are resonant with the signal to be received. Having said that the information in the accompanying table can be useful in fault finding !
Whilst we`re on the subject......
RF isn`t a DC voltage*, it`s AC, and it`s not just AC but very high frequency AC. In fact for TV/FM/DAB we`re talking MHz (where 1 MHz equals one million Hz). When measuring the dipoles I used a standard multimeter set on Ohms, but I also tried a 100 kHz ESR [Effective Series Resistance] meter (i.e. I was checking the impedance at 100kHz) and I still got more or less the same results as I did with the multimeter at zero Hz (i.e. DC). It would have been interesting to see what results I`d have got (particularly across the baluns) using an ESR meter working at 600MHz ! On the other hand, in some circumstances only 50Hz can make a big difference in impedance. If you used a meter on Ohms to check the winding of a mains transformer it`d read dead short but to mains AC [at only 50Hz] it certainly isn`t short circuit, if it was it`d blow the fuse (or the winding).
With relevance to this article one should always bear in mind that AC currents can be induced from one circuit into another (that`s how transformers work) so in actual fact you don`t always need continuity [as read by a multimeter on Ohms] between two points on a particular circuit for the signal to pass between them.
AC = decreases as frequency rises
DC = open circuit
Inductor / Coil / Winding
AC = increases as the frequency rises
DC = short circuit
AC = constant as the frequency rises
DC = constant as the frequency rises
If you start putting coils and resistors and capacitors in networks/circuits you then start getting some very odd results (i.e. resonant at certain frequencies), and that`s the basis of RF transmission and reception.
* AC = Alternating current (like mains electricity) DC = Direct Current (like from a battery)
The modulated output (from RF2) on most Sky boxes is about 70 dBμV, which equates to a medium strength signal, and as such it can often feed two points with a passive splitter, provided the cable runs aren`t too long. Note that if the Digi Link system is required this will not usually work through a splitter, even one with power pass, see below.
The “loop through” RF (from the aerial) is usually amplified slightly, about 4 dB, which is about the loss you`d get through a 2 way splitter. Thus if the output from the RF2 is fed into a 2 way splitter you`ll end up with what you had at the input to the Sky box, this obviously excludes any losses in the cable run(s).
The 9v (and, often, the IR return path signals) from the RF2 output on the Sky box will pass through a splitter (e.g. an F conn splitter) with power pass, but only from the output to the input, i.e. not in the direction required to actually use the splitter as a splitter ! However, it should be noted that certain types of 2 way CoAx splitters (e.g. the ones we sell) seem to work the Digilink system [when only splitting 2 ways]. It`s not really recommended and you will obviously only get half the signal out of each leg, but you could experiment to see if it works for you, if you`re really that desperate to save £15 odd. If you need to feed more than one point and require Digi eyes to work the correct method is to use a Digilink amp. Also see using a diplexer for Digilink.
If using a diplexer to add a Sky (or CCTV) signal to another UHF/VHF signal [e.g. from your TV aerial] a diplexer (of the type we sell) will pass the Digi link / IR return path signal and its accompanying 9V, but only on the low leg, i.e. not if the Sky output is connected to the high leg. For example the received signal from Emley Moor (or Winter Hill or Sutton Coldfield etc etc) could be connected to the high leg (and the RF2 connected to the low leg) of a CH36 or CH38 diplexer without losing any of the transmitter`s output. Note that any FM/DAB signals must be routed through the low leg !
The diplexers aren`t actually specified to pass the IR return/Digilink frequency but it does work, in fact whilst experimenting to see just what you can do with diplexers we found the Digilink signal will pass quite happily through two diplexers in series (either way). Note the power pass switch on the diplexer must be set to “on”, for the the 9V from the Sky box to pass through, but if done so the voltage will pass and (if necessary) will work this remote powered Digilink amp.
Services (options menu) > (highlight “Settings” [spanner]) Select >
(highlight “Picture”, then press) 0 > 1 > RF Outlets > Select
Standard box = (press) Services > 4 > 0 > 1 > Select
If you`re short of pre installed cables you can send more than one signal through one downlead, even in different directions !
Note that the TV point next to the Sky box would not receive the signal from the aerial(s).
Use of a diplexer to achieve this distribution layout is only possibly if your TV transmitter is group A, B or C/D. Group B and C/D signals will enable the Digilink system to work by enabling the TV aerial to be connected to the high leg, see
The frequencies used (i.e. into the set top box) by cable TV companies are generally in the range 5MHz up to 860MHz, or, sometimes, 45MHz to 860MHz. That is to say VHF and UHF.
The signal can be split to feed more than one set top box by using a splitter capable of handling that frequency range, our F conn splitters will work for that. You will obviously suffer a 3 dB attenuation through the splitter and, in fact, when the cable company add a splitter to your system they would usually turn up the power slightly to compensate for this loss. I`m not an expert on cable boxes but the vast majority of tuners in TVs would normally cope pretty well with a fall off in signal of 3dB, assuming the original signal was of decent amplitude, obviously. If necessary, having tried the splitter on its own first, you could try adding a variable gain amp in front of the splitter. The two way mains amp we sell goes down to 47MHz but this may well work down to 5MHz, and, in fact, some say that non return path amps are more likely to work below their specified 47MHz then return path amps and our preferred model of mains amp is a non return path model. Remember that not all cable systems use the 5 to 45MHz band anyway.
This method works for many cable boxes, including models by Telewest, NTL and Virgin Media.
Unplug the Box > Wait 20 seconds or so > Hold down the “Up” and “Down” select buttons > Whilst holding buttons down plug box back in and wait 10 to 20 seconds > Box will boot up in Engineer or DIAG mode > Use OSDs to reset RF channel.
Not sure what the official way to get out of Engineer mode is but unplugging the box, waiting,
then plugging it back in again works !
Note that some of the V+ boxes* do not have an RF output, or even an RF input come to that, which, I have to say, is very poor design. If you`re ordering a V+ box I`d ask whether you can have one with a modulated RF output, certainly if you ever want to set it up like a Sky system and watch what is on it in any other part of the house. If they supply you with one that has no RF output, you then need to buy a modulator. So I`d complain to Virgin that their crap design has meant you`ve had to shell out, and mess about generally, so you`d like them to pay for said RF modulator. Personally speaking, I think you`d have a case.
Incidentally, apparently there`s some rumour out there that the Virgin V+ box doesn`t give out a signal from the SCART socket when the HDMI is in use. Well one of or customers said he set up one of our modulators off said SCART and it worked fine regardless of whether HDMI was selected or the programme was in HD (though obviously the signal from the SCART and modulator would only be in standard definition).
* Virgin`s version of Sky+ (or Freeview+), i.e. can record and also pause live TV etc.
Aerial gain tests (full results) now has its own page
* Actually there is one TV/Sat diplexer that will enable powering of a mast head amp, but that does it by using clever electronics to detect the mast head amp then supply 12V to it by utilising the DC power from the satellite box. Thus, technically, it hasn`t got through power pass because if you removed the satellite tuner then the mast head amp would stop working, regardless of whether you had a PSU on the downlead.
Using the correct UHF/UHF diplexer you can also send the RF2 signal one way and the signal from your aerial the other (though only if your transmitter is grouped).
It`s like magic isn`t it ? ! ? Here we`re sending a satellite IF frequency signal down from the loft) and a UHF signal (in this case the RF2 output from a Sky box) back up the other way. An additional refinement of this is that the Digilink (IR Return) signal will still work but only if the distribution amp is mains powered (like this one) as opposed to one which is remote powered by the Sky box. The reason is that the diplexer can only have power pass* on the satellite leg if the LNB switching is to work correctly, thus the 9V sent to power the eyes (or the remote amp) can`t pass. However, the IR return signal can pass so we just need to add the voltage for the eyes from the mains powered amp.
A Zone 1 dish is smaller than a Zone 2 so therefore has less wind loading.
On the other hand a Zone 2 dish has about 2dB higher gain so should give you a more reliable signal, e.g. less chance of "rain fade".
It is recommended that all sites in Scotland use a Zone 2 dish.
Because the Zone 2 dish has a higher gain (and therefore a smaller acceptance angle) alignment of it is more critical.
Obviously the great majority of people fit the Zone 1 dish, and apart from a bit of "rain fade" they generally work acceptably.
A Zone 1 dish is approx 43cm x 58cm. A Zone 2 dish is approx 56cm x 75cm.
Watch out for LNBs with short LNB F conn weathershields.......
The problem with splitting signals from a satellite dish to a number of receivers (as opposed to the signals from one satellite receiver to a number of TVs) is that the LNB on the dish can work in four different modes according to which satellite programme is being tuned into by the box. The four modes are :
Horizontal polarity -
Horizontal polarity -
Vertical polarity -
Vertical polarity -
Straight away one can see that if (to receive the desired programmes) the receivers happen to require different modes at the LNB then that is impossible, and that is why you can`t split the signal from one LNB to a number of receivers.
However, life is never as simple as that.
If two receivers linked to one LNB by a splitter, are, by pure chance, tuned to channels which both require the same mode (e.g. horizontal polarity high band) then both receivers may well work fine, assuming the signal is large enough to still work after losing 5 to 6dB through the splitter.
Furthermore, if the LNB is split to two points but only one receiver is ever in use, then that too can work, again subject to there being enough signal to cope with the splitter loss (5 to 6dB satellite IF frequency). In both cases the splitter must be capable of working up to satellite frequencies (not all are) and have power pass on both outputs, the internal F conn splitters we sell fulfil both criteria.
So, if one LNB can only supply one receiver, the obvious question is, how do you supply signals to multiple receivers (or even one Sky+ box, which needs two separate feeds) ? After all blocks of flats haven`t got hundreds of dishes on the side walls have they ? Not usually anyway.
There are two ways round this, one LNB can have multiple outputs, two, four or eight being the commonest, though I have to say having four, or even worse, eight, cables coming out of your satellite dish and down your wall, can look pretty crap. You can make it look neater by using twin sat cable, but an eight way would still need 4 lots of twin cable....... We sell 4 way (Quad) LNBs, though you don`t have to use all four outputs if you only require two at the time you fit the system.
for possible use in the future. However, because there are a number of different dish fittings, we don`t sell them Online, only in the shop or over the phone. Carefully remove your old LNB, ensuring you don`t disturb the alignment of the dish, bring it in to the shop if you can (and we`ll check the LNB we stock fits your dish) or we`ll tell you what to measure to check we send you the right one.
The other way, used in most large systems in flats, is to use a Quattro LNB (which supplies all four modes of LNB operation simultaneously) linked to a multiswitch. The latter then needs a separate cable from each of its outputs to every receiver (or two to every Sky+ box), but it can then supply any of the 4 LNB modes as required by each of the receivers. These are not simple setups and the dish should be 80cm or more to increase the signal to noise ratio (though 60cm can be used if desperate and the dish is close to the multiswitch), i.e. not just a standard Sky dish, which the Quattro LNB wouldn`t fit onto anyway. We do not sell Quattro LNBs or multiswitches.
If you`re going to all that trouble to get Freesat, I have to say it`d be a lot simpler, and cheaper, to install an aerial system capable of receiving Freeview........
The low band frequencies (into the LNB) are from 10.7 to 11.7GHz and high band frequencies are from 11.7 to 12.75Ghz. These are down converted in the LNB by the use of a local oscillator into satellite IF, ranging from 1 to 2GHz.. This is the signal which travels down the cable into the satellite receiver.
Horizontal polarity is selected by the receiver supplying 18 volts to the LNB, vertical polarity by the receiver supplying 13V to the LNB.
High band is switched on by a 22kHZ tone being sent to the LNB by the receiver, and low band by the absence of that tone.
Thus it can be seen that if two receivers (connected to one LNB via a splitter) both want different modes from the LNB certain priorities apply. If either receiver has the 18 volts switched on (for horizontal polarity, as opposed to the 13 volts for vertical polarity) then horizontal polarity will be switched on at the LNB. Similarly with high and low band, if either receiver has the 22kHZ switched on then that is what the LNB will switch to.
Some people just want an alternative point to use their satellite box or PVR. Thus they don`t actually need to split the signal at all if they use looping cables as in the diagram. Don`t use cheapo crappy unscreened wall plates though, use decent ones like these.
UHF TV frequency wavelengths
Wavelength = Velocity ÷ Frequency
Speed of light = 299,792,458 m/s
To calculate the wavelength (in cms) divide 30,000 by the frequency (in MHz).
This should be accurate to 0.07%, which is accurate enough for most RF applications....
The frequencies given in the table are for (most) digital MUXES, for analogue channels deduct 3MHz (see article above the table).