How Far Can You Run A Coax TV Aerial/ Satellite/ Sky Cable?
If you’re planning you own TV aerial or satellite dish installation and require a particularly long length of coax cabling between your antenna and your TV, or if you want to connect your outbuilding/ shed etc., which may be some distance away with a reliable TV signal, read this article for all you need to know. In this blog I discuss maximum lengths of coax cables, signal losses and how to overcome these with things such as amplification. Without any further ado, let’s begin.
Minimum & Maximum Signal Strengths For TV/ Satellite Signals
To help understand the blog. It’s important to understand what the suggested minimum and maximum signal strengths when measured in dBµV. If you’re thinking maximum signal strength? It can get too strong? Yes, you read that correct and its very important to understand maximum signal loads. below are suggested minimum and maximum signal loads for each respective service. As long as the distribution equipment can handle it, you can exceed the maximum signal levels but you must not allow this to enter your TV when it's too strong, use an attenuator if necessary. It's very important that you do not let the signal drop beneath the minimum at any point, even if this will enter another amplifier later in the system.
Suggested signal levels
Satellite TV: Minimum - 47dB (ideally 52dB), maximum -80dB
DTT/ Freeview/ TV Aerial: Minimum - 45dB (Ideally 50dB), maximum - 80dB
Analogue TV: Minimum - 60dB, maximum 80dB
DAB Radio: Minimum - 40dB, maximum 70dB
FM Radio: Minimum - 60dB, maximum - 75dB
Coax Cable Signal Losses
Before we go any further and something that I’m sure you’re already aware of, is the longer the coaxial cable the more signal will be lost but why is this? If you can remember back to a your school science days and Ohms Law, you will know that a voltage drop along a length of a conductor directly relates to the length and size and that conductor. Fortunately, as TV aerial and satellite signals are converted in to the dBµV scale complex calculations are not required, providing that you’re using a correct 75ohm coax cable. Below are some typical signal losses of various types of coax cable. These are all good quality cables that are double screened with solid copper, centre conductor, copper screen and braid. Cables that do not utilise copper conductors will not perform as well in terms of signal performance. Single screened coax cables, which do not have a foil screen will perform significantly worse that below, especially at the higher frequencies and must not be used for satellite signals.
Cable Attenuation(db 100m) 470Mhz 860Mhz 1350Mhz 2150Mhz
WF65 21.7 30 37.5 48.4
WF100 13.3 18.3 23.4 30.3
WF125 10.9 14.5 19 24.8
WF165 8.9 12.5 16 20.9
You can see from the above that there is a massive difference between WF65 cable, which has a 0.65mm centre conductor and is commonly used for Sky satellite dish installations or other satellite PVR’s that require two coax inputs, when compared to the larger cables sizes. The most extreme of these being the WF165 coax cable which has a 1.65mm centre conductor and a difference of nearly 28 dB attenuation over 100m at the higher frequencies used by satellite signals. Larger conductor coax cables exist still but these are very uncommon and cost quite a lot to purchase.
In reality “shotgun” cables will only be used for domestic environments and relatively short cable distances and WF165 cable will only normally be used on large communal satellite TV systems with very long cables lengths but you get the idea.
Cable Losses Increase With Frequency
The higher the frequency the signal on the coax antenna cable, the greater the signal losses will be. For example, a satellite LNB connection which typically operates between 950-2150Mhz (wideband LNB’s 300-2150Mhz) will lose more signal over cable distance then a TV aerial signal will which operates typically between 474-698Mhz (formerly up to 850Mhz). This is effect is even more if you wish to send DAB signals (215-230Mhz) or FM Radio signals (88-110Mhz) as these use even lower frequencies too. You will need to consider this before choosing the coax TV cable you will use. If you have a particularly long satellite cable run for example, it’s not a good idea to use a smaller conductor “shotgun” style cable.
Cable Length & Communal TV Systems
There are various types of communal TV systems, but the two most common are MATV systems which send a TV aerial signal to multiple flats and a IRS TV system which includes satellite signals. An MATV system will typically have one trunk cable and various taps with drop-in cables to each flat/ apartment, the trunk cable will then continue onto the next tap-off unit. The same can be true for an IRS system, which instead of 1 trunk cable will have 5 trunk coax cables. In both types it’s possible that the signal will need to travel down a long length of cable before it enters each flat/ apartment. This usually means that the trunk cables will be a larger conductor coax cable like WF125 or WF165 to help reduce cable losses. In both systems, it is common to have a launch amplifier at the head-end which will amplify the signals to very high levels so that this can be carried through the TV system. Of course in both systems, you will need to consider other factors relating to signal losses, like losses associated with taps, splitters and wall plates as well as other distribution equipment which may be required.
The difference of signal losses over coax cable length can be very problematic in large TV systems and long cable runs as you have to consider signal losses at different frequencies on the same cable. In large communal IRS systems which are what is usually installed in blocks of flats, the radio, TV Aerial and satellite signals are all combined together on the same cable. Over distance this can cause the higher frequency signals to become weaker in relation to the lower frequency signals. When viewed on a TV/ Sat spectrum analyser this can cause a visible slope on the signals which we call “sloping”.
Overcoming Signal Sloping
Overcoming signal sloping is very important as you may have a good signal on the services that use the lower frequencies and a very poor signal on the higher frequencies. There are a few things than can be done to resolve sloping. You could introduce the signals that carry signals on the lower frequencies at a higher level using an pre-amplifier or something similar, you could attenuate the lower frequencies down or most likely you would install equipment that allows you to adjust the slope. A lot of amplifiers and distribution equipment that are used for communal TV system will have slope correction built in or have an adjustable slope mechanism built in, this is usually done with a small screwdriver.
Amplification To Overcome Signal Losses
If you’re going to lose a lot of signal down a length of coaxial cable which could be cable resistance or losses associated with the TV signal splitters which can make your signal too weak causing poor TV reception, breaking up and pixelation. Fear not amplifiers can be installed to overcome this. It’s important when introducing amplifiers that you buy the correct type and install this correctly.
Install Amplifier Before Signal Is Weak
You want to install your amplifier in a location where the signal is still of an acceptable strength, before cable losses have taken effect. For conventional TV Aerial systems the best place to amplify a signal is up near the antenna usually using a masthead amplifier which can also be powered off the same connecting coax cable that provides the signal. You do not want to introduce an amplifier after the resistance from the cable length has caused to drop the signal too low, as the amplifier would be trying to boost something that is not there.
Careful Not To Overload Equipment
Every piece of TV aerial/ satellite equipment will have a maximum signal strength that it can handle and the signal level in your system should never be allowed to go beyond this as this could overload your equipment and cause poor TV reception, including loss of signal and pixelation. It could even damage the parts/ components of the equipment. If you need to amplify the signals to very high levels like is the case for communal TV systems, you will need a professional launch amplifier to do this which can carry a high signal strength through it.
Satellite Line Amplifiers
Simple satellite line amplifiers can be installed which has a sloped signal gain to remove sloping and are powered by the satellite receiver can be installed to overcome signal losses on long cable lengths. The problem with these though is if they’re installed too close to the dish, the signal will become too strong and if they are installed by the satellite receiver, the signal can be too weak. For this reason you will need to install the line amplifiers mid-way of the cable length, usually after 40-50m if using RG6/ WF100 type cable.
Consider Fibre Optic Cabling For Very Long Runs
If you have a very long distance that you need to send a TV signal, consider using fibre optic cabling instead which distributes the signal using light rather than copper conductors. This means that there is virtually no signal loss at all between optical transmitter and receiver. You will need to calculate the cost of the fibre equipment in your workings but I can assure you pulling a single fibre optic cable compared to five large coax trunk cables is significantly easier and takes far less time and you will not have the signal losses/ sloping to worry about!
As the fibre optic signal is virtually loss-less, with the right equipment you can send TV Aerial/ satellite signals over kilometres! The equipment required for terminating fibre optic cabling can be expensive but you can buy pre-terminated fibre optic cables which just plug in, I recommend erring on the side of caution and buying pre-terminated fibre slightly longer than you think you need as you don’t want to come up short. The excess can simple be coiled at either end. For your reference most fibre equipment for TV systems using single-mode fibre and FC/ PC connections.
How To Calculate Coax Cable Losses
As already mentioned, the dBµV scale makes working out coax cable losses very easy. You simply take the frequencies that you wish to carry down the cable. It’s a good idea to calculate your signal losses at the highest frequency to work out how much signal will be lost down a length of cable. The same process should also be performed for the lowest frequency and mid-range frequency to identify any potential sloping or signal imbalances in the TV system. To do this:
1- Find the highest frequency that you wish to carry through a coax cable.
2- Identify your required cable length.
3- Identify the signal attenuation per meter on the cable you have chosen (1mm coax is the standard)
4- Multiply the signal attenuation by the metre distance.
5- If the signal loss is too great, consider repeating this process for a larger conductor coax cable.
Maximum Length Of Coaxial Cable
As you can see from this article, that this is a difficult question to answer as there are multiple factors that effect how far you can send a TV signal down a coax cable. This includes quality of the cable, size of the centre conductor, the frequency that you wish to send down the cable, whether amplification will be introduced or not. If you were sending the signals down a 100m cable with a 2dB loss per 10 metres of the frequency you’re carrying, then if you send it down 100m of cable you will get 20dB loss. This shouldn’t be a problem if you’re getting 75dB off of your TV aerial, but if you’re not in a good signal area and get less than 60dB then the cable length will be a problem and amplification will need to be introduced – or a cable with a larger cross sectional area of the centre conductor.
Tips To Overcome Cables Losses On Long Cable Lengths
The following is just the above delivered in a concise manner.
1- Use a good quality cable.
2- Add amplification where necessary, make sure this is installed in the correct manner.
3- Use a thicker diameter/ centre conductor cable.
4- Use fibre optics instead of coax for very, very long cable lengths.
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Until next time,
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