Save Our Spectrum - Frequencies
Analogue transmission of TV programmes
Analogue technology requires a TV channel with a width (frequency requirement) of 8 MHz to transmit TV programmes. 7 MHz are needed for broadcasting the TV programme, leaving a gap of 1 MHz used primarily by reporters with wireless microphones.
Structure of an analogue TV channel: 1 MHz gap used by wireless microphones
Analogue broadcasters need protection distances between each another: a broadcaster’s transmission frequency has to be allocated at the appropriate distance from another broadcaster to avoid massive interference in the overlapping area. This is occasionally noticed by TV users when there are overshoots.
The use of available transmission frequencies therefore varies between regions, particularly as areas that are hard to access (valleys) need their own transmitter as well. Protection distances created for this purpose are free spaces where transmitters do not operate, and are used by radio and TV broadcasters and their production companies for, among other things, wireless microphones for programme production.
Advantages of the digital broadcasting of TV programmes
Compression processes can be used for the digital transmission of content. These enable 4 TV programmes to be broadcast in one 8 MHz TV channel – in some regions, people are talking about 6 or even 8 programmes. The greater the compression, the lower the actual picture and sound quality, and the more susceptible they are to interference.
Four digital TV programmes in one 8 MHz wide TV channel - no more channel gaps!
Digital dividends
There will be four digital TV programmes in one frequency range where one analogue programme used to be transmitted. In theory, therefore, the digital frequency requirement for transmitting TV programmes is reduced to a quarter of that of analogue. This “saving” – having three quarters of the band theoretically freed up – is known as a digital dividend. These frequencies can be given to other services, meaning the number of programmes can be increased.
For good or ill! The last IFA consumer electronics trade fair in Berlin in 2008 featured mobile phones with the capability of receiving DVB-T. These programmes are transmitted in the UHF range, which is why many programme suppliers who until now could only be received on cable or satellite are pushing for the UHF range. Without a presence there, they would be cutting themselves off from anticipated advertising revenue: the essential source of revenue for private broadcasters.
However, can three quarters of the UHF band really be used for other services? This is hardly likely as the 1 MHz gaps used by reporting services have to be taken into consideration. 47 channels can be used in the entire UHF band, which means there are 47 1 MHz gaps, that is a total of 47 MHz – a considerable spectrum in which a large number of these services are operating to produce programme content.
While wireless microphones can also broadcast digitally, they are not allowed to use compression processes. There is no frequency gain here! (See also “Digital wireless microphones - do not compress!”)
Directive 91/2005
In the meantime, wireless microphones and monitor systems have become so easy to operate and so reliable that they are being used for all kinds of events and offer quite considerable potential for economising, particularly when it comes to professional applications!
To use this type of equipment in the UHF range requires an operating permit issued by Germany’s licensing authority, the Bundesne
tzagentur (Federal Network Agency), which details the place of use, period of use and the frequency to be used, e.g. the above-mentioned frequency gaps or unused TV channels. This is practical for fixed facilities like conference centres and theatres, but represents considerable expense for distributors and events that change, both in terms of the technology to be used and administration.
The Bundesnetzagentur is resolving these issues with Directive 91/2005, which enables professional users to work nationwide in UHF channels 61 – 63 (790 – 814 MHz) and 67 – 69 (838 – 862 MHz) without an operating licence. It is important here to listen in before switching on so as not to disrupt wireless links that are already in operation. A frequency gap is therefore sought within this range and the wireless microphone, wireless monitor or reporting link operated within it. According to information from the Bundesnetzagentur, this process has proved worthwhile as the agency is not aware of any complaints.
As matters stand, Directive 91/2005 will exist until 31.12.2015. There is nothing like this practical German regulation anywhere else in the world and it should continue to exist in this or a similar form beyond 2015 too.
Primary service - secondary service
Primary services like TV programmes have priority in the frequency range they are allocated. The secondary service permitted to use a frequency range can use parts of it provided the primary service is not active in it. In the main, wireless microphones are a secondary service and are therefore of lesser importance when frequencies are handed out.
Frequency ranges are only given to primary services. Secondary services have simply been forgotten in the redistribution of the UHF spectrum: “The area is available and unused...” is something that has been written in the press in the past and still appears occasionally today.
In future, something like this will only be prevented if wireless microphones receive the status of a primary service - as more or less outlined in Directive 91/2005.
Use of digital dividends!
At WRC 07 (World Radiocommunication Conference 2007), the 790 – 862 MHz range was only “identified” for possible use by IMT (International Mobile Telecommunications), not allocated! Wireless internet access in rural areas should be possible in this frequency range in places where DSL cabling is not currently allowed.
This “identification” by the WRC 07 includes the very area described by Directive 91/2005 and therefore means the end for wireless microphones as no alternative frequency range has so far been made available: i.e. wireless microphones have lost another 48 MHz in the spectrum!
There are high ranges in the UHF frequency range, making it easier to open up rural areas. Several villages can therefore be reached: signals have to be available in buildings.
According to a calculation by the IRT (Broadcast Technology Institute) around 450 connections with a 16Mbps data transfer rate have been set up in the 790 to 862 MHz range: “At best, rural areas can be opened up in patches, but blanket coverage is not possible.”
It is also doubtful whether these investments in rural areas are worth it over the long term: you can only get a return on investments in this technology in urban areas where there are plenty of users to access it. This technology would therefore be a waste of valuable spectrum because DSL is already available in urban areas via cable.
Furthermore a requirement has been put forward for 4 channels (32 MHz) for authorities and security-based services. With the internet usage indicated and the authorities’ channels, around a third of the UHF band has practically been awarded already.
On top of this is the fact that in the near future the technical quality of TV is going to be improved from SD (Standard Definition) to HDTV (High Definition) which requires more spectrum.
Things are therefore getting very tight, because TV services currently operating in the 790 – 862 MHz band have not yet been included in this consideration and also have to be bundled together in the range below 790 MHz.
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