Hillsborough
Sheffield
S6 2LL
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Appendix
Where I put stuff when I can`t think of anywhere else to put it.......
Appendix Index
UHF Channel Numbers to Frequency etc (also see Selecting an RF modulated channel)
UHF / VHF frequencies to wavelengths
Sky Digiboxes General Information (on the RF output/loop through)
Splitting Signals From A Satellite Dish
Cable Boxes : Resetting RF outputs
Installing a chimney lashing kit
Distribution system utilising a M/H amp, a tap, and two splitters
Larger distribution system utilising a power amp, taps and splitters
Test results (full) of Group A aerials
Test results (full) of Group B aerials
Test results (full) of Group C/D aerials
Test results (full) of Group K aerials
Test results (full) of Group E aerials
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 related to the frequency thus :
Fv = 8n + 303.25
Where Fv = Frequency of the vision carrier in MHz and n = Channel Number.
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 documents :
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. If 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.
UHF TV frequency wavelengths
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 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 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 ! Also see using a diplexer for Digilink.
If you need to feed more than one point and require Digi eyes to work use a Digilink amp.
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.
In addition, the power pass switch on the diplexer must be set to “on”.
So long as the low frequency leg is used (and the power pass switch is on), the 9V from the Sky box will also pass through and work this remote powered Digilink amp.
FM and DAB signals as well as TV can also be looped through the Sky digibox, as they can through Digilink amps.
Services (options menu) > (highlight “Settings” [spanner]) Select >
(highlight “Picture”, then press) 0 > 1 > RF Outlets > Select
Sky HD box =
Accessing the hidden service menu, used for switching on RF2, and/or, altering the frequency/channel of the RF2 output.
Be very careful what options you change in these menus, particularly the satellite dish settings !
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).
Further points.
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 windward side of the
stack preferably with a cranked pole. If possible fit an end mounting aerial (e.g. a Log40) 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.
4 At this point, with the lash loosely assembled round the stack, bend out the lugs on the corner pieces, then push them under the lash wire and into place on the other three corners of the stack.
5 Now tighten the bolts sufficiently to firmly secure the bracket against the corner of the chimney.
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.
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.
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 (and not painted, or 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 75 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.
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 !
Splitting Signals From A Satellite Dish
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 -
satellite frequency +
2 x through power
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 5 to 6dB splitter loss. 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, but you don`t have to use all four outputs if you only require two, you`ve always got them
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.
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.
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.
Note. Some "experts" say just wrapping the lash round the J bolt is sub standard and it should be 'spliced' to prevent slippage. Well I`m telling you, and them, that the above lash would never slip, absolutely no chance whatsoever. I`ve seen lashes only wrapped once round the J bolt which haven`t slipped in 20 years. Personally I would never recommend a single wrap, but it just proves a double wrap is slip proof.
Cable Boxes : altering the channel of the RF output.
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.
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.
Utilising a 12/1.7 dB tap, and allowing a 2dB cable loss from the tap to the 8 way splitter, would give the following readings throughout the system (all relative to those at the input to the tap).
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 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.
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. All our splitters (except the CoAx one), taps and mains amps (except the 2 way amp) have earth bonding terminals.
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). 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. 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.
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.
What does amuse me is that there are people out there who are scared stiff of getting a mains shock, but then they go speeding in their cars ! ? ! And that`s far more likely to kill them.....
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.
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......
Such is the Black Art nature of RF all aerial test readings are approximate, in fact
as far as I know no lab will guarantee accuracy better than +/-
It must be admitted that these particular results are less accurate than that (unlike our TV aerial tests) but they still give a pretty reliable indication of the relative performance of the various antennas.
The “variable” figures result from the directional nature of the particular aerial.
This doesn`t apply to the TV aerials, they`re variable because they`re not even designed
to pick up VHF frequencies ! Note that if the 3 element aerials were pointing directly
away from the transmitter you`d probably lose more than the -
Standard box = (press) Services > 4 > 0 > 1 > Select
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