Today there were a couple of momentary outages of our fibre broadband internet connection. We're not sure whether the BT Infinity service was at fault, or whether the Draytek Vigor 2860 router just had a senior moment.
Co-incidentally when we turned the TV on later in the day there were none of the terrestrial channels available. Streaming channels and satellite were still working, but nothing from the transmitter in the Gorge.
I checked the BBC's reception service which reported the transmitter was working fine.
But following the link it appears the transmitter had been through some maintenance earlier in the day. Exactly what maintenance is left to the reader's imagination.
After a quick check with an alternative aerial, the only thing left to do was re-tune the BT TV box. Sure enough, the maintenance activity has changed the frequencies that the channel multiplexes were transmitted on.
Delving a little deeper into the need to update the transmitter, it is due to a process called the "700MHz clearance". According to OFCOM: "In November 2014 we decided to make valuable spectrum in the 700MHz band available for mobile data as soon as practicably possible." As terrestrial TV is broadcast between 474MHz and 786MHz, this means that some of the spectrum currently used for TV is being reallocated for mobile data. Note that the Digital Switch Over (DSO) from terrestrial analogue to terrestrial digital TV was only completed in 2012.
So Digital UK, the body behind terrestrial TV in the UK, have come up with a plan to overhaul the multiplexes and frequencies that each transmitter broadcasts, with a view to freeing up the 700MHz band by the end of 2020.
"Following a decision by Ofcom, spectrum in the 700MHz UHF band currently used for digital terrestrial television (DTT) is being reallocated for the development of future mobile services. Some DTT multiplexes will be moving to new broadcast frequencies as a result of this change. Engineering work for the 700MHz Clearance Programme will take place at transmitters across the UK between 2017 - 2020. Freeview viewers (and those with other services that use Freeview channels, such as YouView) will need to retune their TV equipment when changes take place in their area."
Today was the day that the Ironbridge transmitter was scheduled in the clearance programme. Digital UK considers the Ironbridge transmitter to be a part of the Sutton Coldfield transmitter group, rather than The Wrekin group. On page 11 of their January 2018 update for the Central area are the details of the Ironbridge transmitter changes:
RF channel 49 is right on the 700MHz upper limit, and channel 58 finishes at over 770MHz, so all of the previous multiplexes were being transmitted in the band that OFCOM wants to clear. Our current aerial is a Wolsey/Triax HG5 yagi, which is good for receiving channels 21 to 60 (T group), up to the previous 800MHz upper limit on TV transmissions. At the end of the 700MHz clearance in 2020 this aerial is going to be picking up mobile data transmissions as well as terrestrial TV, so will need to changed to one that only picks up channels 21 to 48 (K group).
Additionally we have a Triax TFMV 22W masthead triplexer and amplifier that works up to 862MHz. In theory if the aerial isn't supplying it any signal above 700MHz, then the fact that it can amplify signals up to 862MHz isn't an issue. But no aerial has a perfect frequency response, so it might be worth changing the TFMV for an amplifier with a 700MHz maximum frequency, or put an inline filter between the aerial and the amplifier.
Strangely Digital UK's coverage checker reports that the previous aerial group was K (21 to 48), not CD (48 to 68).
This is incorrect, as a K group aerial is limited to channel 48, and therefore could not pick up the D3&4 multiplex previously being transmitted on channel 58. It also states that the aerial polarisation was, and will be, vertical, whereas the current aerial is definitely horizontal. I think I'll take what it says with a pinch of salt.
Co-incidentally when we turned the TV on later in the day there were none of the terrestrial channels available. Streaming channels and satellite were still working, but nothing from the transmitter in the Gorge.
I checked the BBC's reception service which reported the transmitter was working fine.
But following the link it appears the transmitter had been through some maintenance earlier in the day. Exactly what maintenance is left to the reader's imagination.
After a quick check with an alternative aerial, the only thing left to do was re-tune the BT TV box. Sure enough, the maintenance activity has changed the frequencies that the channel multiplexes were transmitted on.
Delving a little deeper into the need to update the transmitter, it is due to a process called the "700MHz clearance". According to OFCOM: "In November 2014 we decided to make valuable spectrum in the 700MHz band available for mobile data as soon as practicably possible." As terrestrial TV is broadcast between 474MHz and 786MHz, this means that some of the spectrum currently used for TV is being reallocated for mobile data. Note that the Digital Switch Over (DSO) from terrestrial analogue to terrestrial digital TV was only completed in 2012.
So Digital UK, the body behind terrestrial TV in the UK, have come up with a plan to overhaul the multiplexes and frequencies that each transmitter broadcasts, with a view to freeing up the 700MHz band by the end of 2020.
"Following a decision by Ofcom, spectrum in the 700MHz UHF band currently used for digital terrestrial television (DTT) is being reallocated for the development of future mobile services. Some DTT multiplexes will be moving to new broadcast frequencies as a result of this change. Engineering work for the 700MHz Clearance Programme will take place at transmitters across the UK between 2017 - 2020. Freeview viewers (and those with other services that use Freeview channels, such as YouView) will need to retune their TV equipment when changes take place in their area."
Today was the day that the Ironbridge transmitter was scheduled in the clearance programme. Digital UK considers the Ironbridge transmitter to be a part of the Sutton Coldfield transmitter group, rather than The Wrekin group. On page 11 of their January 2018 update for the Central area are the details of the Ironbridge transmitter changes:
RF channel 49 is right on the 700MHz upper limit, and channel 58 finishes at over 770MHz, so all of the previous multiplexes were being transmitted in the band that OFCOM wants to clear. Our current aerial is a Wolsey/Triax HG5 yagi, which is good for receiving channels 21 to 60 (T group), up to the previous 800MHz upper limit on TV transmissions. At the end of the 700MHz clearance in 2020 this aerial is going to be picking up mobile data transmissions as well as terrestrial TV, so will need to changed to one that only picks up channels 21 to 48 (K group).
Additionally we have a Triax TFMV 22W masthead triplexer and amplifier that works up to 862MHz. In theory if the aerial isn't supplying it any signal above 700MHz, then the fact that it can amplify signals up to 862MHz isn't an issue. But no aerial has a perfect frequency response, so it might be worth changing the TFMV for an amplifier with a 700MHz maximum frequency, or put an inline filter between the aerial and the amplifier.
Strangely Digital UK's coverage checker reports that the previous aerial group was K (21 to 48), not CD (48 to 68).
This is incorrect, as a K group aerial is limited to channel 48, and therefore could not pick up the D3&4 multiplex previously being transmitted on channel 58. It also states that the aerial polarisation was, and will be, vertical, whereas the current aerial is definitely horizontal. I think I'll take what it says with a pinch of salt.
