Improvements to Freeview transmission mode information

Following the changes to the commercial multiplexes that are now being rolled out over the main 80 transmitters, I have improved the information shown on the site.

^{Brian Butterworth published on UK Free TV 29th October 2011 at 09:15}

On each transmitter information page, there is a three-line description for each multiplex that lists the configuration used.

The first example shown here shows the new mode being used for the commercial multiplexes:



64QAM shows the number of "symbols" that are transmitted within each subcarrier, in effect in 8x8 positions. 8K is the number of subcarriers (which is actually 6817) used within the 8MHz UHF signal. 3/4 (three quarters, or 0.75) in this example is the amount of "forward error correction" used.

The second line shows the bitrates provided - in this example 27.1 megabits (million bits) per second.

The third line indicates the transmission standard used - DVB-T and the type of video encoding used, in this case MPEG-2.

The second example is from the Winter Hill transmitter, where a local television multiplex is broadcast:



Here the QSPK is a 2x2 position system, and results in only 6.0 megabits per second.

The third example shows the standard post-switchover configuration for the public service transmitters.



PSB1 and PSB2 use 64QAM, 8K (6817) but with forward error correction of 2/3 (two thirds, or 0.67). The use of this form of error correction provides 24.1 megabits per second.

PSB3 is used for Freeview HD, this showing on the third line as DVB-T2 MPEG4. DVB-T2 is a more advanced transmission system, with a number of enhancements over DVB-T. MPEG4 is also a newer, more efficient video encoding system.

The use of a 256QAM (16x16) symbol positions and 32KE (that's 27841) subcarriers results in a broadcast of 40.2 megabits per second.

The final example is from Rowridge, a transmitter in a pre-switchover state:



The low power digital transmissions use 2K (1705) subcarriers with a 16QAM (4x4), which results in 18.1 megabits per second per multiplex.

Bitrate comparisons

Compared to pre-switchover multiplexes 1, B, C and D:

• Pre-switchover 2 and A: 33% more
• Post-switchover PSB1. PSB2: 33% more
• Post-switchover PSB3: 122% more.
• Local TV: 67% less
• Post-switchover COMs after changes: 50% more.