Why Do Some Sat/ Sky Boxes Have Two Cable Inputs?

October 2, 2020
by
Tom

What Do Satellite Receivers/ Sky Boxes Have Two Satellite Inputs?

 

Here is my latest offering, asking why do some satellite receivers, including Sky and Freesat boxes have two satellite F connections? Believe it or not, there is more than one potential reason for this as some satellite set-top-boxes have two F connectors for one reason and some have two connections for another reason. In this blog, I discuss the most common reasons. Let’s begin.

 

Twin Tuner Satellite Receiver (PVR)

The most common reason that a satellite TV receiver will have two LNB connections is because it is a twin tuner model, commonly known as a PVR which is an abbreviation of Personal Video Recorder which usually has an in-built HDD for storing recorded TV directly onto the unit itself so you can watch back at a later date. Examples of twin tuner satellite receivers are Sky+, Sky+HD and Freesat+ boxes, sometimes branded as Freetime but many other versions exist for the various satellite services around the world like Tivusat, Polsat, TNTSat and so on.

 

Why Does A Satellite PVR Need A Twin Tuner When Terrestrial Doesn’t?

A logical and good question that you could ask yourself is, why does my satellite PVR need two satellite dish connections when a terrestrial model doesn’t? This is all to do with how the universal LNB works. I will be writing a detailed blog at a later date about this but I will summarise here, because the satellite signals are beamed to earth on higher frequencies within the Ku band utilising a greater bandwidth than the intermediate frequency band (which is what the universal LNB oscillates the signal down to, one which the coaxial cable can contain) allows the LNB cannot provide all the services down the coaxial cable. The satellite LNB switches between one quarter of the services at any one time depending on what channel has been selected to view or record. Each quarter of the satellite services is most commonly referred to as a satellite band, these are horizontal low, horizontal high, vertical low and vertical high. The horizontal/ vertical element refers to the polarisation of the signals and the high/ low element refers to those services broadcast in the higher or lower part of the satellite KU band.

 

If a standard twin tuner Sky box didn’t have two satellite feeds you could only view/ record one quarter of the satellite services at onetime, meaning if your were to set a recording and wanted to watch a service that was on one of the other 3 quarter satellite bands this wouldn’t be possible. Terrestrial based PVR’s which receive from a TV aerial/ antenna do not have to content with a switching signal so the signal can effectively be split inside the PVR itself.

 

Wideband LNB Connections

Many new satellite PVR’s like Sky Q boxes and third generation Freesat receivers which are manufactured by Arris do not use a universal switching LNB, so you may wonder why does a wideband LNB system required two satellite inputs? The wideband LNB obviously has to contend with the issue above of having to squeeze a greater broadcasting bandwidth (satellite KU band) onto the coaxial cable.

It achieves this by separating half of the signals onto one of the two connecting cables and the other half of the channels/ services onto the other. This means that if you have a satellite STB/ PVR that requires a connection to a wideband LNB and is otherwise not compatible with a universal LNB like Sky Q boxes, you must have two separate coaxial cable inputs connecting between your wideband LNB and you satellite RX because if you didn’t, you would only receive half of the available channels which isn’t great is it? Technically a Sky Q box can be connected on a single feed with a full range of services but you must have a dSCR system and the box set up in SCR mode which is another kettle of fish altogether.

 

For your reference if you have purchased the new Freesat wideband system and have a conventional universal LNB system, it will work it’s just you will be limited to one/ tuners giving you the ability to view/ record up to two programmes at one time whereas with a WB LNB and two cables connected you can watch up to four. Which brings me nicely onto my next point, as there is not switching the boxes can divide the signals internally in the PVR to feed more tuners, this allows more channels to be viewed/ recorded at one time. It’s been a time coming but apparently in the works with the Sky Q system the one dish/ main Sky Q box will be able to connect up to 7 additional Sky mini-boxes, whereas at the time of writing this you are limited to 4.

 

Wideband LNB Utilise A Greater Frequency Bandwidth

Important to note that separating half the channels down each connecting coax cable is not the only mechanism that is used to prevent the need for LNB switching. It also achieves by oscillating down to a frequency range greater than the satellite IF band which universal LNB’s use, it does in fact oscillate the signals down and right over the top of the part of the UHF spectrum that is used by terrestrial TV services like Freeview and some telecommunication frequencies like 4G all the way down to 300Mhz.

 

Satellite Out/ Sat Loop

There is another type of connection that is common on many generic FTA receivers but is not commonly used because of the LNB switching system, which is the Sat-out connection which is another female F connection that looks exactly the same as a twin tuner, albeit with different labelling. This isn’t actually an input, but is an output connection which is designed to be fed onto other satellite TV receivers, like many pieces of terrestrial TV equipment does. The obvious problem with this type of system with a universal LNB is that the “looped” signal will only make available one quarter of the services according to which satellite band that the first satellite receiver has selected. This effectively creates a master/ slave relationship where you would have to select a channel on the main receiver to be able to receive a desired channel on the “slave” satellite receiver.

 

Coincidently, the day that I’m writing this I installed a dish for a customer that had two Humax Foxsat PVR receivers installed side by side(temporarily) and wanted to connect one with a twin satellite feed and the second via the ‘LNB Out’ connection. I talked him out of it in the end because of the reason above.

Satellite Services With Broadcasting Satellite Antenna

I have included this on here as it is slightly relevant and you may have a system near you which works on a similar sort of principle. Some satellite dishes can be installed to receive broadband services, in the UK the two most common are Tooway and SES Broadband. It doesn't apply to Tooway as this uses one coaxial cable connection to the Tria but in this case of SES Broadband this has an iLNB with two connecting coaxial cables that feed two inputs on the satellite broadband modem. One is more reception of data(download) and the other is transmission of data(Upload). The two use the same type of F connector so you will need to make sure that you connect these the correct way.

 

Other Types of Coaxial Connection

There are other types of coaxial connection which you may confuse with a satellite twin tuner, LNB out or something similar. I have listed some of the most common below.

Aerial Input

Your receiver may also have an aerial input which many do which also uses a coaxial connection albeit it with a different type of connection.

Aerial Out/ RF Out

Like the LNB Loop connection like mentioned above, the RF Out can be used to connect one aerial signal to multiple devices except the RF out connection is far more useful than the ‘LNB Out’, as there is no LNB switching to contend with.

RF2 Out

Some satellite receivers like Sky+ and some earlier models of Sky+HD boxes have two separate ‘RF Out’ connections, called an RF2. This allows the box to connect to two or more TV’s which you may have in other rooms. In the case of Sky boxes the installation of a remote eye by your second TV allows to you turn over your Sky box from the second room.

Coaxial Audio Connection

Another connection you should be aware of and I have seen people try to connect an antenna in, is the coaxial audio connection. This is an audio only connection and not something your can connect a cable from your TV aerial or satellite dish into.

 

Satellite Connection Questions – Post The In Blog Comments Section Please

I hoped that you liked this blog, if you have any questions or comments please feel free to POST THEM IN THE BLOG COMMENTS SECTION BELOW and I will answer them as fast as I can. You may need to be patient as I am very busy and may not be able to answer them as fast as you may like.

 

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Again, I hope you liked the article, please check back for more.

Until next time,

Tom

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