A fair proportion of our call outs for "poor picture" are not caused by the aerial
at all, but by the cable. Usually it is perished or cracked or just bodged in the
first place, e.g. a kinked cable or joined together with insulation tape etc etc.
If it is a fringe area and there is a long cable run it could even be due to the
use of "budget Low-
Ever wondered why some aerial installations use loads of tape on the mast, and in pretty imaginative patterns?
No I didn`t think you had, but I`ll tell you anyway.
It`s so installers can recognise their own handiwork ! I hesitate to use the term “tag” because that`s the name used by those scroats who deface so many things with their depressingly ugly graffiti.
Screened surface plates are deeper than unscreened types so make sure you fit a pattress box of sufficient depth. If retro fitting to an existing shallow pattress box then we sell spacer plates to gain an extra 12mm depth. They can also be useful if you want to increase the clearance behind a surface plate so as to ease a kinked cable, also see surface plates incl diplexed. We advise utilising the cable direct from the aerial straight into your TV or Freeview box and placing a "hole tidy" (sometimes called a cable tidy or grommet) around the cable just where it enters the house provides a neat job. It`s quicker / cheaper than a wall socket, and their matt finish means they`re ‘paintable’. Remember that a “retro fitted” surface plate / wall plate isn`t going to be neatly flush fitting (not unless you chisel out the wall.......) and a decent screened plate will require a pattress box sticking out about an inch. We have had customers complaining of poor signal or intermittent interference who have gained significant improvements by simply dispensing with the surface plate (or upgrading it).
Unscrew the plate from the wall and check if you have a bit of slack in the Co-
If you plan to recable your aerial yourself, a typical cable run from the chimney is about 15 m. One should always buy a little more than is required because few things are more frustrating than completing the job only to discover you`re short of cable (which is why our installation kits are actually supplied with 20m ! ).
It is always a good idea to install a service loop of cable (about 5" in diameter) at an inconspicuous location at the bottom of the pole, this can save much time and hassle if you need to subsequently fit an amplifier or splitter.
(note the low percentage screening cover)
Reasonable life ?
(We do not sell this type of cable)
Traditionally everyone used "Low Loss CoAx" for virtually all TV (and FM radio) aerial cable and years ago much of the CoAx on the market was of pretty reasonable quality with high percentage screening cover. The vast majority of low loss Coaxial cable sold these days is absolute rubbish. This is an objective fact and can be proved by just looking at the exposed screening in the picture above. There`s probably only 40% screening coverage on 42 strand "budget low loss CoAx". Don`t get me wrong, if you live in a reasonable signal area and/or the downlead isn`t too long, and/or you`re lucky, it could still work reasonably well, though if the cable is old thin stuff, (i.e. less than 6mm) it really should be changed if possible.
Signal loss is one thing but cheap cable`s real Achilles heel is poor interference suppression. With particular reference to the "Digital cliff edge" it`s just not worth skimping on the cable to save a few of quid. If decent cable prevents just one glitch/freeze on your picture per night (for the next 20 years,,,,,,,) it really is [or should be] a no brainer. How much did your TV cost ?
These days virtually no aerial installers use low loss CoAx, even the Bodgers don`t (usually).
The high power 4G transmissions make good screening even more important, be warned !
Most new build houses used ultra cheap CoAx to wire up the pre-
In my opinion nobody should be fitting (or even selling) "Low Loss" coaxial cable.
The vast majority of brown (or sometimes white) downlead is of the budget Co-
Typical loss (per 10m at 800MHz) of "Low Loss" CoAx is approx 2.7 dB, i.e. a typical 15m run would lose just over 4 dB (a 6dB loss is half )
(We do not sell this type of cable)
(We only sell this type of cable)
The third type of cable also has "double screening", but this time the foil is copper. This WF100 / CT100 grade of cable is the best of the generally available types, though when I say generally available it`s not usually sold at DIY shops.
The high power 4G transmissions make good screening even more important, be warned !
To be frank, this cable is overkill for DAB/FM (i.e. VHF) but being a perfectionist I like that. There isn`t a big difference in attenuation between copper foil and alloy foil (RG6 type) cable on UHF [or even satellite], but copper/copper cable lasts significantly longer, which is why (at one time) Sky only recommended this grade, but with higher "churn rates" and a desire to make as much as poss, they`re not quite so fussy anymore ! Whatever the pros and cons, the price difference on a typical 15m run is only a few pounds, so why not fit the best ?
Only about 5 to 10% of aerial installers use copper/copper satellite cable, the vast majority use RG6 because it`s a lot cheaper, remember they`re using loads of it so it makes a significant difference to how much money they make. Thus, if you have to get an installer to run your cable(s), but you want to ensure copper/copper is fitted, I`d buy it yourself and then get them to fit it, but (discretely) make sure they fit the cable you`ve bought !
This cable is suitable for FM, DAB, TV and Satellite, and it is CAI / Sky approved. Our cable is the foam filled type as opposed to air spaced. Although signal quality wise there`s no difference between them, foam filled tends to resist kinking slightly better. Furthermore if you`re unlucky enough to get water into the cable then foam filled tends to resist water running down the inside of it better than air spaced, though it can still permeate down through the outer braiding under certain conditions. Cable diameter 6.7mm (average).
Remember, if decent cable prevents just one glitch/freeze on your picture per night
(for the next 20 years........) it really is a no brainer, or should be.
Typical loss (per 10m at 800MHz) for this type of cable is 1.8 dB, i.e. a typical 15m run would lose just over 2.5 dB (a 6dB loss is half )
We sell copper/copper satellite grade cable in black, white, brown, red, yellow and green,
NOTE ! : When splitting this type of cable it should be done by pulling one core forward and the other back, not sideways as this increases the risk of the outer insulation splitting.
Also known as twinsat or shotgun use of this variety of satellite cable has mushroomed since the advent of Skyplus / Freesat+ (which requires two separate feeds from the LNB to feed its two tuners) but the cable can also be used for any install requiring two separate feeds from anywhere to anywhere, e.g. from two separate (i.e. not diplexed) aerials.
If you need to run two cables it`s neater and the 2 cables can easily be pulled apart to run the final distance(s) as individual runs, and they are often routed to two way surface plates, i.e. 2 cables in > to 2 sockets. You do need special (wider) clips to tack it to the wall though !
There are two main types of Twin cable, the first is comprised of two standard cables (approx 6.5mm ea) and its performance is exactly the same as the individual cable would be.
We only sell this variant, in black, copper/copper and foam filled.
However there is also a second type composed of two thinner cables (approx 4.5mm ea) and its performance is really pretty bad, see the graph above. Obviously we do NOT sell this cable. The thinner cable has two advantages. First it`s significantly cheaper. Second it fits through the standard size drill holes that most installers use. This is why Sky has sanctioned its use despite its performance being so inferior that a well known manufacturer hinted to me (off the record) that they were ashamed to produce it. Even Sky only recommend its use on runs up to 20m, though many in the trade would only use it up to 10m, and the most quality conscious aerial installers would only use it up to, well, 0m.
Of course, this isn`t to say it won`t work fine if it`s a short run, or you`re just lucky, just as with "Low Loss" CoAx. Many bodges in this trade, and indeed in life, work for many people, but that doesn`t make them right. These people have obviously never heard about 4" Fence Posts, and they wouldn`t pay the extra for them even if they had.
The thinner cable does have another disadvantage, standard Co-
The best method of getting the cable into the loft, if that`s where it`s needed, is through the end wall/gable, but some roofs (i.e. hipped types) do not have an end gable, so if you need to get the cable into the loft how do you do that ? Well I have to say that is an awkward problem.
There are two approaches, preferably try to get the cable in through the soffit, but if that`s not possible then lift a slate and push the cable under that. If there`s a lining under the slate you`ll have to cut a hole in it to get the cable in, then try to tape it up or silicone it. Bear in mind the lining should never get any water on it anyway, not if the slates are in good condition.
Typical cable run (incl "service loop")
Cable through walls (not your window frame.....)
Whilst on the subject of cable / connectors, it is preferable to avoid the use of
Surface Plates but if they are utilised make sure they`re quality screened non-
The high power 4G transmissions make good screening even more important, be warned !
Cheap unscreened faceplates can be especially problematic,
in fact only bodgers use them. or even sell them.......
ATV only sell screened non isolated wall plates.
When using a wallplate the extra join in the downlead that is required is unwelcome (though not that significant) but the cable is often "kinked" [at the point where it is attached to the PCB at the rear of the plate] and this is bad practice from the RF point of view, so try to route the cable like the one below left and not like the other one. The capacitors in isolated wall plates, particularly 'budget' types, can also cause significant signal loss, personally I don`t recommend isolated TV outlet plates, not for domestic installations anyway.
Wall plates can be useful for looping across to an alternative TV point though !
If your downlead is cut through, best practice is to replace the lot. It may be budget Coaxial and cable does degrade over time anyway. If you must join a new length of cable outside, we recommend using the method shown below. CoAx plugs covered in insulation tape is how Bertie (as in Bodger) would do it....
Or do I route it forward, round the cradle, and then down the pole ?
Well we did a series of tests and found no measurable difference. I`m not saying there isn`t any difference, I`m just saying we couldn`t measure it. It certainly looks worse if you route it back round the reflector though ! To help prevent the ingress of water don`t forget to introduce a slight downward gradient to the cable (where it exits the aerial`s junction box), or, if the aerial is a Log Periodic, tilt it up at the front !
Next use decent quality insulation tape to secure the cable to the outside of the pole. Make sure you stretch the it a bit whilst you wrap it round, and remember to keep the tape warm in your pocket if using it in the cold weather ! The use of cable ties is not recommended as they degrade in the sunlight and when they fail you don`t want to have to go back up to replace them. Running the cable down the inside of the mast can also be problematic due to the possibility of chaffing on the cut end of the pole, plus any wind movement can cause the downlead to bang against the inside of the tube in a most annoying fashion. Lastly, if you run the cable down the North side of the pole it will minimise exposure to the sun (clever ehh.....).
We sell a cable joing kit consisting of 2 x F connectors, an F-
Note, we stock a superior type of Fconnector.
We`ve frequently been asked whether it`s OK to run Co Ax next to mains cables and, to be frank, we didn`t really know for sure. We finally got round to trying to find out in Aug 2008 with a simple but, we feel, appropriate experiment.
We taped a 12m length of Low Loss CoAx, and of copper/copper satellite cable, to a mains flex. Then we used a signal generator to supply the signal, and at the fairly low level of only 65 dBμV as well, to try and encourage as much chance interference as possible.
But how to detect the noise ?
We used a spectrum at first, but really that was just trying to be flash because a TV is just as likely to reveal any interference !
As an electrical load we thought a vacuum cleaner would suffice, and as ours is 1800W it should certainly draw some current, and hopefully generate a few mains spikes on start up.
We connected up the Sat cable, then rather tentatively we switched on the vac, there was no interference whatsoever. We then switched the vac on and off repeatedly to try and generate some spikes on the mains, still no interference. Next we used a 6dB attenuator to drop the signal even further, still no interference. Finally we routed the cable bundle through 20ft of alloy tubing to simulate ducting and keep any radiated interference close to the Co Ax (?). Result ?
Still no interference.
We also repeated each experiment with ordinary Low Loss CoAx, and I have to tell you that in this test there was no detectable interference with that either. That said, I have heard of cheap Low Loss CoAx introducing RF crosstalk to adjacent cables when bundled together, although this obviously isn`t at 50Hz main frequency. But see below......
That all seemed cut and dried, and in fact I even put the first draft of the results on the website, but something in the back of my mind was nagging away at me.....
I decided to repeat the experiment with a load which may generate more electrical noise.
I dragged out my trusty 1980s Black & Decker drill and thought I`d use that as a load instead. Incidentally those were the days when B & D made decent tools because that drill has had some use, and I mean some right hammer, and it still works fine, other than a replacement chuck.
I checked that when used right next to the set it did actually introduce noise to the screen, and it did if one “played” the switch and the variable speed (under load).
The vac on the other hand didn`t produce any noise thus indicating that the above tests with it were only valid for electrical loads which are suppressed, which most are to be fair.
Using the copper/copper satellite cable (with the mains cable from the drill taped to the side of it) there was no interference on the set or blocking on the Freeview box we used as a test. But, and this is significant, as stated above there was a bit of noise if the drill was operated right next to the TV or the digital STB. The drill was producing noise, which can interfere with the tuner(s) by direct radiation, i.e. nothing to do with the signal cable.
But when the drill was operated at a distance of more than a few metres away (when using the satellite cable) there was no interference introduced to the signal via the cable.
We then repeated the test using Low Loss CoAx and I`m pleased to say that my negative opinion of it was vindicated. With the signal cable taped to the mains cable from the drill there was significant interference on the screen and blocking on the Freeview box.
Just to be sure we swapped back and forth between them and the results were consistent.
I thought “Low Loss” was crap, but I didn`t think it was that crap.....
We were in the swing of it now, so we next tried RG6 type satellite cable and it was far better than Low Loss. In fact there was hardly any difference between it and the copper foil type cable (the big difference between alloy foil and copper foil type cable, is how long they last..... ).
Picture of cable bundle exiting the tubing and supplying the signal to the TV, just behind it.
Freeview picture whilst under test with satellite cable.
Freeview picture whilst under test with “Low Loss” cable.
To quote that well known idiom “all that glitters is not a decent fly lead” (or something
like that) and this picture illustrates this perfectly. The top lead looks very flashy,
gold plated in fact (gimmick, unless you live in a salt mine......) and it`s “Standard
Linear Bandwidth” no less -
Remember looks aren`t everything, substance wins over style in my book, every time. This is the fly lead we stock (at 2m in length) and they really are good. The 6mm “double screened” cable is well worth having (though this cable is probably even better quality) but what`s just as significant is the crimped on plug, no weak soldered joint here.... What was interesting is that even the suppliers couldn`t tell us if the plugs were crimped on, the only way we could tell was to cut the lead open ! Also note the RF chokes, normally hidden under the blue plastic covering and the strain relief moulding (where the cable enters the plug) to ease any curve in the cable.
To be honest I can`t understand why we don`t sell even more of them !
Also see feedback on fly leads
Obviously it is preferable to have a continuous cable run with no joins in it. Unfortunately this is not always possible and if the following method is used, a join which would be reasonably acceptable can be made. Screw an F connector onto each end and then utilise a “Back to Back” to join these two ends together, see picture below. If the joint is outside then self amalgamating tape must be used to waterproof the joint, not ordinary insulation tape. Cut off about one foot (we sell it by the foot and also by the 10m reel) and then remove the backing layer ! Start wrapping the tape round the joint about two inches above the join (stretching it to about half its width whilst you do so), ensuring you overlap the tape be at least half its width, then finish the same distance the other side. If possible (and it isn`t always possible) try to install the joint so that the cable runs downwards either side of it [so water will run away from the joint], better still place the joint where it is sheltered, e.g. under the eaves. No cable should be installed where it is under strain but obviously this is even more important where it is joined. Provided this is executed correctly this gives a reliable and waterproof joint.
Push in CoAx connectors can be used for TV (UHF) or FM/DAB radio (VHF), though DAB actually uses F connectors in most cases. F connectors can also be used in place of CoAx plugs (assuming there is a corresponding F socket obviously ! ) but it is very bad practice to use CoAxial plugs/sockets for satellite work. Note, albeit rarely, CoAx connectors are sometimes called as "Belling Lee" connectors, and also, somewhat inaccurately, IEC connectors.
Co Axial plugs are more convenient (as they are quicker to connect) but an F connector
gives a more robust and positive connection, this is particularly important in the
case of connections which require power pass. That said, if your TV or amp has a
CoAx input it is pointless putting an F connector on the end of a cable, then an
F to Co-
One sign of a good quality Co-
It is not advisable to reuse CoAx plugs as the "claw insert" becomes deformed when it is screwed up onto the cable, they aren`t that expensive anyway. If you have an intermittent signal it`s always worth checking the CoAx plug as a loose fitting one can cause this symptom, it may be a low quality plug or it was not even attached correctly in the first place ! Whilst checking the plug examine it for signs of water/dampness, this is usually caused by a damaged downlead, see “clipping cable to the slates”. I actually think fitting CoAx plugs correctly is not that easy, so we supply a leaflet with ours explaining how it should be done. The same applies to F conns. Alternatively we can attach the plugs for you at a small additional charge, see Custom Cables.
NOTE : It is not unknown for the nuts to pull off the body of F connectors (all F connectors…..), so our advice is order more than you need !
Here we have two types of F Connector. We stock the one on the right. It may be a little stronger but what is really worthwhile is the larger nut which make it far easier to tighten. Yet again, something so simple......
Whilst I`m not prepared to say anything for certain, especially with RF, I think it is reasonable to conclude that mains borne interference is not usually introduced to the signal through the signal cable provided it is satellite grade.
The same cannot be said for Low Loss type CoAx cable.
Also see this interesting customer report on cable interference problems.
However even with the best quality cable it is still possible to get interference but that is more likely to be by direct radiation onto the tuner(s). It could also be through unscreened splitters, amps or surface plates or even straight onto the aerial, though Baluns are supposed to limit the effects of it and Log Periodics even more so. Also try tilting the aerial up at the front a bit.
It is also possible to get noise up through the mains and the use of filter type mains adapters may help with that, may being the operative word because all TVs/STBs should normally have internal mains chokes anyway.....
The best remedy for interference is to track down the cause and cure it at source, e.g. if your central heating thermostat is noisy and creating electrical interference replace it with a suppressed one. Other significant causes of interference for digital TV can be cordless phones, particularly digital ones (try moving the base station away from the TV or STB) and LED lights / lighting. We`ve had more than one customer who has cured the latter problem by swapping crappy cable for copper / copper satellite cable. Once we had a report that a blue tooth adapter was knocking out reception of CH56 ! Not sure how ! ! The moral of this story is suspect everything RF / EM spectrum related ?
The high power 4G transmissions make good screening even more important, be warned !
Having said all of the above, I`d still only route CoAx cable next to mains cable if I really had to.
But if you have no choice I`d definitely make sure it was satellite grade.......
Finally, in addition to decent cable, always use screened amps, splitters & face plates.
The CoAx plug fits on the end of a TV aerial lead and it pushes in to the TV`s Co-
Note that most FM tuners actually have a male connectors. So in that case a female CoAx is needed (or a male with a Back to Back coupler).
Note, right angle adapters (male to female) convert normal plugs to right angle plugs.
Finally, and almost ironically, there is the ”Quick F”, an adapter to convert a screw F connector to a push F connector, i.e. a female screw on F to a male push in F.
Now I know what you`re thinking, isn`t this an abrogation of the whole point of F connectors (to give a better connection and also one which cannot be pulled apart) ?
Well yes, but these adapters are often used where the connection is screwed and unscrewed regularly, e.g. caravan based satellite systems, and also, if you think about it, satellite installers !
Various adapters are available to convert a Co-
"Back to Back" joining barrels convert a Male Co Ax to a female. We do not recommend female CoAx sockets (except right angle types) because the design of the “in line” type is not conducive to reliability. Very few trade aerial suppliers sell them either, and that`s got to tell you something.
"Right Angle" plugs (Co Ax and F Conn) are available for use in confined spaces, remember sharp bends in CoAx cable are a bad idea, particularly immediately as it exits the plug. When considering the use of right angle connectors there is a theory that some can cause impedance mismatch with a consequent effect on the signal. So, if you do experience signal problems when using a right angle connector try temporarily eliminating it and see if the fault clears. I`d have thought most people wouldn`t find a problem, but it`s worth bearing in mind.
This is the lower quality grade of satellite cable, but even the cheapest is far
better than "budget low loss" CoAx. The major difference between satellite cable
and "low loss" Co-
The high power 4G transmissions make good screening even more important, be warned !
With RG6 type cable the foil is usually aluminium or some similar material, although the cheaper brands seem to use a mylar film sprayed with conductive paint. To be quite honest it`s perfectly suitable for virtually all TV/Radio (i.e. UHF/VHF) applications and this is particularly true if it is a branded product, e.g. Webro. Although Sky don`t (didn`t would be more accurate, they`re more bothered about the cost now ! ) recommend this grade of cable this is more to do with the fact that RG6 type cable doesn`t last as long as copper/copper type cable because the braiding on alloy foil type type cable can oxidise over time (dissimilar metals), particularly if used outdoors. Apart from that I would say that RG6 is fine for most satellite use provided the down lead is not of excessive length. Most aerial installers these days (90 to 95% ? ) use RG6 cable because it`s far better than "Low Loss" but doesn`t actually cost that much more. On the other hand RG6 is much cheaper than the (superior) copper/copper type, thus explaining why so few use the latter......
Note, RG6 is technically the size of the cable (i.e. 6mm in diameter), and as such
Typical loss (per 10m at 800MHz) of RG6 type cable is about 1.9 dB, i.e. a typical 15m run would lose just under 3 dB (a 6dB loss is half )
The stuff on the right is absolute crap.
Manufacturers aiming at the uninformed DIY market (e.g. Philex/SLX, amongst others) make this sort of stuff. If any of them would like to sue me I`ll see them in court, but I`m rather unconcerned, because I know I`d win. Assuming, of course, that the judge knew anything about aerial installations........
4.9mm in diameter.
Crap unscreened weakly constructed
Crap plastic unscreened CoAx plugs.
Crap unscreened plastic surface box.
I only found out how crap this stuff was when a customer came into the shop wanting to buy some CoAx plugs to fit the 25m cable kit he`d just bought from Argos. We don`t stock CoAx plugs to fit thin 4.9mm cable, and neither does anyone else I know, because it`s so, well, crap.
Also see feedback on fly leads.
To be fair to the customer he bitterly regretted purchasing said kit, but, unfortunately, he`d already run the cable under his fireplace !
Note. As with most bodges I`m sure there are many situations where this crap would work fine. If the signal was strong enough, or if the person installing it was flukey enough*, and if the plastic components didn`t get handled too much (and fall apart).
* As defined by the poorest quality on the retail market as at Sept 2011
* In my experience bodgers generally do tend to be flukey.......
Bypassing a budget type isolated surface plate gave an increase in signal of nearly 2 dB on average ! To put that into context that`s almost as much as the increase in signal you would get by swapping from a Log 36 (a medium gain aerial) to a DY14WB (a high gain aerial). Furthermore the elimination of the surface plate also gave a huge improvement to C4 Teletext (remember that ? ) which had always been problematic at this location. The gain in signal level cannot have been due to a decrease in the number of “connections” because the plate (one connection) had actually been replaced by two, i.e. Plug > Back to Back coupler > Plug. The fact that the surface plate was an isolated type was very significant because when the isolating capacitors (which were 3nF at 3kV) were shorted out most (but not all) of the attenuation disappeared.
We sometime get people insisting that crimp on F connectors are superior to screw on types.
Well I have to say that from the electrical point of view there`s no difference between them at all.
As for "pull off strength" I have to admit that crimp on is a bit stronger, if it`s done right of course. But even with screw on Fs, assuming the correct F is used for the cable (they aren`t all the same, our Fs are correct for our cable) it won`t pull off, not unless it`s subjected to a force it never ever should be. Anyway, this is all irrelevant, because if you pulled hard enough on a correctly attached screw on F connector the nut would usually pull off the body long before the screwed on body pulls off the cable !
So why do many aerial installers use crimped on Fs ?
That`s nothing to do with the quality of the connection. It`s more to do with the fact an installer, particularly for system work, might have to put on hundreds of Fs per day, and for that crimping saves a hell of a lot of strain on your hands/wrists.
But I thought you were singing the praises of your Quality CoAx leads, mainly because they`ve got crimped on connectors ?
That`s correct. But that`s to do with the fact that plugs on cheap fly leads are moulded on and the centre core soldered, which can then break as the moulded plug flexes, therefore it`s a weak point. That problem doesn`t apply to screw on Fs.
(note the presence of an additional aluminium screening foil).
Suspect life ?
(note the presence of an additional copper screening foil)
The best screening.
The longest life.
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.
If you`ve found this site informative and, hopefully, interesting as well,
Graph of cable loss (in dB per 10m) for the three main cable types.
Note how at the FM frequencies the losses are far lower than at TV and satellite IF frequencies. The latter are the lower down converted frequencies from the LNB. Also note the poor performance of the thin type double satellite cable.
See article on the maximum recommended distance from a Sky dish to a receiver.
Replacing crappy cable already installed in walls. Well that`s an awkward one. Most aerial installers won`t attempt this, just in case the cables part company in the wall as they`re being pulled through and the customer then demands (somewhat unrealistically in my view......) the cabling is "returned to how it was before". Anyway, you can only try this if the cable run is 'loose', that is to say you can pull it at one end and it moves at the other. Cut the old cable square at the end and butt join onto the new cable by tightly winding some decent quality insulation tape round the join. Don`t use too much, because you don`t want the overall diameter to be much greater than the cable itself. Now gently pull it through, hoping it doesn`t get snagged half way up. If it does get snagged, pull it all out again and try the same process from the other end. If that doesn`t work, forget it and run a new cable down the outside wall.
Incidentally, if installing cabling in walls you should always use trunking, this is for a few reasons, not least because cable can absorb moisture from the plaster and then start corroding, particularly if it`s not copper copper !
If installing CoAx cables for a distribution system in the walls of a new build or rebuild (i.e. where it`d be difficult to recable) we recommend installing two decent quality cables to each point. This will help future proof the install even if you don`t need them at the moment, like if the Government ever threaten to switch off the terrestrial signal and force everyone to have satellite...... (Advice emphasised 19 Sept 2012) It`s also a good idea to use two different colour cables so you can identify which is which when you`re at each end. On the subject of which, if you`re up in your loft trying to work out which cable has come from which room, try temporarily shorting out the cable and then checking with a multimeter at the other end which cable reads dead short.
We sometimes get people asking us whether they should use silicone grease on connectors. Well I have to say I`ve never met an aerial installer who uses it, and that includes those I know do a good job, and I don`t use it either. We`ve never been to a job where use of silicone grease would have prevented the customer`s problem occurring in the first place. Oxidation between the cable and the connector is not a problem, unless you suffer water coming down the cable. But the latter will also have knackered your cable plus whatever it`s plugged into so under these circumstances worrying about oxidation at the connector is like being concerned over the flat tyre your car`s just suffered whilst being written off in an accident.....
This thing about silicone grease may be a throwback to the days when Mast Head (outdoor) splitters and amps weren`t drained and ventilated as well as most of them are today, ours certainly are. I can`t honestly see why it should be necessary, other than in a very damp cellar. But if the aforementioned cellar was damp enough to require the use of silicone grease then you shouldn`t be putting anything electrical down there anyway. And if you did the damp would have played havoc with the amp or splitter (that the plug is connected to) long before you should start worrying about the plug !
Conclusion : If you want to use silicone grease go ahead, I can`t see it doing any harm, but I really don`t think it`s necessary.
I can`t actually think why the screening on the above abomination is like it is. One possible reason is it makes it easier to solder it onto the barrel of the CoAx connector, and yes, it is just soldered on, not crimped.
All decent cable should be double screened cable, the budget cable above is effectively only single screened. It is also important the plug is crimped to the end (see below) rather than just moulded on with the centre core soldered, because there are few things more annoying than an intermittent connection in your fly lead. In our experience this is most often caused by the centre core breaking off (at the soldered joint) where it`s been put under stress.
The easiest way to spot a crap fly lead is to check how thick (or thin) the cable is, it should be at least 6mm in diameter. That said……. We stripped down a budget flylead which was marked RG59 (not, possibly significantly, RG59U) and despite being not far off 6mm in diameter it was appalling quality. The braiding wasn`t even acting as a screen, it, such as it was, was all grouped on one side as a “drain” wire !
If you have a wall socket (which we don`t recommend, not budget unscreened types anyway) then you need a lead from there to the set. Fly leads are relatively cheap so make sure you buy a decent one. In fact Digital UK advise (in their Aerial Installer Newsletters) that "blocking/sound disturbance is often due to an old or damaged CoAx fly lead running between the TV/STB and the wall plate". When they say "often" they only mean in about 5% of cases, but then again it`s a cheap thing to eliminate, so try it! The new high power 4G transmissions also make good quality fly leads (plus decent cable from the aerial and screened wall plates, obviously) even more important. You have been warned ! See this customer report.
If you`re splitting the signal always use a splitter, never just bodge it together with insulation tape. It is often neater and more convenient to split the cable outside and this can be achieved by utilising a weatherproof splitter box (or an external amplifier). If using an amp, particularly a high gain type, try to avoid running the input and output cables side by side, as this can sometimes introduce "crosstalk" to the signal, especially if using cheap crappy cable.
If you accidentally damage the brickwork*, whilst drilling the hole, we sell “blow out covers” in brown or white. Incidentally these are just to cover up any “blown out” brick work, they are not primarily for preventing water ingress, you should silicone the hole and use a “drip loop” (just under where the cable enters the wall) to do that.
Hole covers are normally siliconed to the wall but can also be tacked on or even screwed on. When drilling a hole through the wall it should usually be done from inside to outside and with a slight downward inclination to help prevent any possibility of water ingress.
* NOTE ! : Damaging the brickwork (when drilling a hole out for a cable run) is very easy, particularly if using an SDS driller. If the hole is in a conspicuous place it`s even more frustrating. My advice is to research the depth of the wall (e.g. at a nearby window or door) and mark that on the drill. When you get close to that indicator drill very carefully. In fact try turning the hammer action off or even swapping to a normal percussion drill.
If any mains sockets are present in the area a hole drilled in a spot diagonally away from them should reduce the chances of hitting the cabling (don`t quote me on this……).
It may be easier to drill a hole through the window frame but it is bad practice to route the lead this way. It will encourage rot and if you replace your window(s) the cable will then need to go through the wall anyway. Incidentally if you ever have replacement windows fitted, do not allow the installers to "wedge" the cable under the frame. Apart from the fact it looks awful and the crushing of the cable should be avoided, when you eventually have the downlead replaced (cable does degrade over time) the old cut off stub will be left in situ for evermore !
The piece of cable in the above picture was run over a roof without utilising clips to secure it and the action of the wind has worn it away on the slates. Water can then seep into the hole and this can have a deleterious effect on the signal. Worse still is what can happen when the water reaches whatever the cable is plugged into......... Incidentally foam filled cable tends to impede the water using your cable as a fall pipe rather better than air spaced cable !
The picture on the left is of a “slate clip” in use. Care should be taken not to crush the cable beneath the wire(s).
A Slate Clip is simply a few strands of galvanised lashing wire (as found in our lashing kits) cut to around a foot long, then bent into the shape in the picture and wedged under the slates to secure the cable. The number of strands used would depend on how the tight the slates are against each other.
Try to avoid running cables over roofs (it will suffer maximum weather exposure there) but if you have to it should be clipped to the roof slates at regular intervals to prevent it moving in the wind and being worn away by the slates. The resulting holes let in rain water which seeps down the cable and ruins your TV tuner, or whatever else it`s plugged into. If you have had an aerial installed, always check to see if the installer has clipped the cable to the roof slates and unless he`s got a cast iron excuse *, I would insist that he does so. Any cable over a roof should run perpendicularly straight down it. Apart from the fact that a diagonal run looks terrible this will also stop any snow build up (remember that ?) from putting strain on the downlead.
* severe access problems would be mitigating circumstances.
Careful thought should be given to which colour cable you use, and be particularly thoughtful whether white is the right choice. Remember cable can be painted if required, which is useful if the house changes colour during the cable run, or you have a white house but the cable also runs over the roof. In the latter case a white cable over a roof (usually dark in colour) looks terrible, so go for black or brown cable and paint it where it runs over the white walls.
Watch out for white.....…
Whilst routing downleads do not introduce sharp bends or kinks to them, the minimum recommended curve being about 10x the cable`s diameter, so 7mm cable would equate to around 7cm, or more if possible. If running a cable round a corner (between two walls) removing a bit of mortar will ease the curve. Note that foam filled cable is a bit less likely to kink anyway.
Always use the correct size clips for the cable. This is for two reasons. Firstly it`s important to avoid crushing the cable, secondly the correct size clip will hold itself onto the cable (rather than you holding it with your fingers) whilst you hammer it in, thus avoiding the possibility of said hammer greeting your finger tips. And that, I happen to know for a fact, is something Derrick gets a great deal of satisfaction from doing. He can be so callous sometimes.
Horizontal runs across brickwork should use a clip every other brick (i.e. about every 18”), vertical runs should use a clip every 8 courses (i.e. about every 28”). Try to fix the top and bottom clips of the run first, then add the intermediate clips, this helps to ensure a straight run rather than looking like a dog`s hind leg...... And always use perpendicular runs (vertical or horizontal) because, let`s face it, diagonal runs look absolutely crap.
Lastly, what do you do if the clips won`t stay in because the mortar`s too soft and crumbly ? First try using longer pins/nails (you might have to drill out the hole in the clip) but if that doesn`t work then unfortunately you have to bite the bullet and put the clips into the bricks by drilling small holes, packing them with wood, and tapping the clip pins into them.
Can a cable be tested (preferably in situ….) ? You can easily test a cable but only for basic short [s/c] or open circuit [o/c], not for any (lack of) screening or impedance matching problems. Short circuits with cable are actually more common than open circuit issues, this is certainly the case with new cable, which, very rarely, can be faulty ! To test for s/c ensure the ends of the cable are not connected to anything, then use a meter (set to Ohms) across the centre core and the screening, obviously no reading should be registered. To test for o/c temporarily short out the centre core and screening of one end of the cable then connect the meter between the centre core and the screening (on the other end), a short (or at the very most one or two Ohms) should be indicated.
All TV, FM, DAB, and/or satellite downlead should be 75 Ohm impedance* in order to maintain an "impedance matched system", but there are 3 main types of RF coaxial cable and they are listed below.
* The impedance of the cable is mainly dependent on the ratio between the diameter of the inner conductor and the inside diameter of the outer conductor, also see 50Ω / 75Ω impedance mismatch.
The temptation to run a cable under a carpet can be hard to resist. Sometimes it seems the only way and the cable is hidden as well, everyone`s a winner it would seem. STOP ! Never run a cable under a carpet, and this is particularly the case where people may walk on it. The cable won`t last long before it`s squashed, then you`ll have to take the carpet up and replace the cable (if you`re bodging it) or replace the cable and reroute it if you`re not…. You have been warned.
There is another type of CoAx used in RF transmission / reception, 50 Ohm (50Ω) cable. It must be stressed this is not suitable for TV / FM / DAB / satellite installs, as we have seen the latter use 75Ω cable, using 50Ω would give an impedance mismatch . 50Ω cable is generally used for amateur radio type jobs. We sell RG58 military specification 50Ω cable.
Actually, there is a fourth type of cable, “triple screened” HD Coax cable, e.g. HD100. I have to say I`m dubious about how worthwhile this product is, particularly as standard F connectors don`t even fit it. Bear in mind that in our impulse interference tests there was no significant RF noise admitted even to the cheaper lower quality RG6 (alloy screening foil) type cable. Copper/copper cable (best type = WF100) is one stage better than that and in addition, as discussed above, doesn`t have the susceptibility to dissimilar metals oxidation of the RG6. Lastly, but just as importantly, HD100 has the same loss / attenuation (29.0dB per 100m at 1750MHz) as WF100 ! So, I have to say, I can`t really see the point of HD100, thus, we don`t stock it. Obviously if you`ve got a load of it free (and the connectors of course ! ) then by all means use it, but I personally don`t think there`s any significant difference.
Short of clearance ?
Have you sufficient clearance (around the CoAx socket connector panel) on your TV to enable you to use a right angle plug ?