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As most Australian and New Zealand readers know, there has been a huge shift in the television landscape with the move to digital and the subsequent closure of the analog service. You may think that the disruption is over . . . but think again! There is more to come – and it has the potential to severely impact TV viewers around Australia and New Zealand. W ith the closure of the analog TV service in Australia and the “digital restack” most of the TV channels numbered 52 to 69 (695-820MHz) have become unoccupied. And as we saw in September 2014 SILICON CHIP, there are many thousands of low-power audio devices, mainly wireless microphones, which also currently use this band and will have to vacate by January 1 2015. As a result of the restack, the Commonwealth Government agency ACMA was able to sell this spectrum (plus 140MHz in the 2.5GHz band) for almost $2 billion, which represented a significant windfall to the government. In fact, the Government refers to this as the “digital dividend”. The intended use for this spectrum is mobile broadband using 4G/LTE technology in the new 700MHz band. This should not be confused with the existing 4G service in the 2.5GHz band. Australia is not alone in reaping benefits from the move to digital – the New Zealand Government sold a similar spectrum for $NZ270 million to TelecomNZ, Vodaphone and 2degrees. The restack Mobile broadband and TV services cannot easily share the same portion of a spectrum as the risk of mutual interference is too high. Fig.1: this is the Australian 4G/LTE frequency allocation – it shows where your old television frequencies have been reallocated to. The winners here are the growing mobile data services. 86  Silicon Chip siliconchip.com.au BLOCK A Band 3 (VHF high) BLOCK B Band 4 (UHF) BLOCK C Band 4 (UHF) BLOCK D Band 5 (UHF) Channel 6 Channel 28 Channel 34 Channel 40 Channel 7 Channel 29 Channel 35 Channel 41 Channel 8 Channel 30 Channel 36 Channel 42 Channel 10 Channel 31 Channel 37 Channel 43 Channel 11 Channel 32 Channel 38 Channel 44 Channel 12 Channel 33 Channel 39 Channel 45 Frequency range(s) used on a specific transmitter site 174-195MHz* & 209-230MHz* 526-568MHz 568-610MHz 610-652MHz BLOCK E Band 5 (UHF) Channel 46 Channel 47 Channel 48 Channel 49 Channel 50 Channel 51 652-694MHz *195-209MHz (“Channel 9 & 9A”) reserved for DAB+ Digital Radio [capital cities at present] Fig.2: in the restack, Australian RF channels are regrouped into similar frequencies sharing the one tower. In addition all transmitting antennas on an individual site will have the same polarisation, either horizontal or vertical. As a consequence the Commonwealth Government committed $170 million (including advertising) to restack 1500 transmitters in 440 sites, with the restack scheduled for completion by the end of this year. When the analog TV spectrum was laid out many years ago provision was made for a vacant analog channel to be placed either side of a transmitter channel in any one viewing area to prevent mutual interference. Fortunately this is not required for digital TV, which is one of the reasons why digital is more efficient in its use of the spectrum. The restack has allocated all transmissions for a given coverage area to a sequential block of channels. The advantages of this are simpler receiving antenna design, with improved performance. On any one site, the transmitter for each of the five networks is allocated an RF channel from one of the blocks listed in Fig.2 and a 6th channel (a spare) is left unallocated. Note that there are some exceptions – eg, NSW Central Coast & Queensland Gold Coast. They are exceptions because they have nine channel allocations and eight active transmitters on each site, because of overlapping licence areas. The other exception is community TV. However, the Minister for Communications recently announced (on September 10) that Community Television, currently located in mainland state capitals using Block B, would cease transmission as free-to-air services on December 31, 2015 and become solely internet-based. At the time of writing, the various community TV stations were lobbying heavily to have this decision siliconchip.com.au overturned so they could remain on air, using the spare channel which the Minister maintains is necessary for “testing”. Radio frequency channels vs logical channel numbers In the above discussion the channels referred to are radio frequency transmission channels, not the “TV channels” or “logical channel number” which are what the user selects. When a digital TV or set-top-box is being set up it will search through the radio frequency transmission channels starting from RF channel 6. When a signal is received, the logical channel numbers (or “TV channel numbers”) will be stored as labels associated with the radio frequency channel on which they were found. These logical channel numbers (LCN) are transmitted along with the electronic program guide and the actual program material. It is the LCN that the viewer selects to view a program. This means that the viewer selects programs by a network number and not the frequency used by the TV tuner. As an example, in Perth the ABC transmits the same four programs on RF channels 12, 29, 41, 47 and 49. However all viewers select programs based on logical channel numbers of 2, 21, 22, 23, etc regardless of the RF channel being used. New Zealand uses European RF channel numbers, so be careful when comparing them to Australian channel numbers. A similar restack has been used in Europe with blocks of eight RF channels, of which two cannot be used because of potential interference. As part of their restack Europe is selling European channels 57 – 64. In New Zealand most free to air transmitters are on either European channels 32, 34, 36 or 33, 35, 37 with all antennas on any one site using the same polarisation. 4G/LTE – and what it means to you Earlier we mentioned that the broadband mobile service will use the newly-vacated TV channels (and 2.5GHz bands) for providing 4G or LTE (Long-Term Evolution) mobile broadband services to devices like tablets and mobile phones. These are marketing names being used by the wireless broadband companies. Fig.3: frequencies used by USA, Australia, New Zealand and Europe for TV and mobile broadband. The Americas and parts of East Asia use the same 700MHz 4G/LTE band as Australia. November 2014  87 With rare exceptions, not only are combined VHF/UHF antenna not required any more, they are actually likely to cause interference to digital TV reception. If you’re in a capital city (VHF TV only), the UHF section could pick up 4G/LTE signals; if you’re in a country area (mostly UHF TV) the VHF section could pick up a range of unwanted RF. Use the chart opposite to select the right antenna. The amount of interference that may be generated between 4G/LTE transmitters and normal TV receivers is determined by the design of the equipment including the TV antenna, cabling and the receiver. Another factor is the width of the guard band provided by ACMA. This band, at 698.5MHz, separates TV services using frequencies below 694MHz from 4G/LTE using frequencies above 703MHz (inclusive). New Zealand has a similar cut-off frequency. Many TV antennas currently on the Australian market are designed to receive RF channels 52-69 along with other channels. This includes old VHF/ UHF antennas and some new band three/UHF “digital” antennas as well as some UHF-only antennas. As a result they will be sensitive to the 4G/LTE transmissions and could therefore make the interference created by this service even worse. Tests have been done to assess the interference to 4G/LTE service by TV transmitters. However no known tests have been done to assess the interference to TV by 4G/LTE! Interference can happen if the TV antenna is close to the device using 4G/LTE or if a mobile phone tower is between the TV antenna and the TV transmitter. The effect is that whenever the tablet or the mobile phone transmits, the TV reception can break up or freeze – and/or the sound can be disrupted. VHF/UHF transmissions to cease nationally Once Community TV stations in 88  Silicon Chip mainland capitals cease transmission on UHF, only a handful of areas may need a VHF/UHF antenna – a few areas where both bands will continue to be used. Therefore, a much cheaper Band-3-only (VHF) design will suffice and should suffer no (or minimal) interference from 4G/LTE. Caveat Emptor – let the buyer beware The first issue for consumers is that imported antennas are often designed for Europe and even the newer designs labelled “LTE” provide no protection from Australian or New Zealand wireless broadband. Also, these antennas often contain a 790MHz low pass filter, which is not much use in Australia/NZ. A second issue is that most of the antennas available from Australian manufacturers are designed to receive up to channel 69 which makes them sensitive to 4G/LTE transmissions. The final issue is that masthead and wideband distribution amplifiers are particularly susceptible to interference from 4G/LTE signals, so they need to contain a 698MHz low-pass filter to remove these signals. For example, the Kingray Edge series and Johansson 4GP series of masthead amplifiers contain the necessary filters. Reducing interference So, what can you do? For a start the TV antenna that you are using should be designed to receive only the channels of the transmitter site for your viewing area. This will maximise the TV signal and minimise interference. This particularly applies to weak signal areas using RF channel 51 such as Newcastle, Illawarra, SW Slopes/E. Riverina NSW, Southern Downs Qld, Murray Valley, Nhill, Geelong Vic, NE Tasmania. Low-powered translators using channel 51 in 154 towns and suburbs around Australia are also susceptible. To determine the RF channels used in your area you should go to http:// myswitch.digitalready.gov.au/ and enter your street address. Click on ‘Channels for…’ and scroll down to ‘Technical information for…’ The RF transmission channels that your antenna will be required to receive will be shown there. The panel opposite titled “Suitable TV Antenna Designs” will then provide you with details of the antenna suited to your location. If a masthead amplifier is required it should not amplify signals outside the range of band 3 (174-230MHz) and UHF (526-694MHz). For New Zealande readers the range is the European channels 26-47 (510686MHz). Existing installations which are suffering from interference and do not contain an amplifier can be improved by inserting a filter at the input to the receiver as illustrated below. This low pass filter will reduce the 4G/LTE signal to just 1/316 of its original power (-25 dB). FROM A NONAMPLIFIED TV ANTENNA TO TV RECEIVER This technique will not work for antennas which contain an amplifier (ie, an antenna that uses a power pack) such as those used on caravans, boats, flat outside and indoor antennas. This is because the filter must precede any amplification. As a further issue the locations used by these antennas often have mobile broadband devices close to the antenna. People who receive their signal via a Master Antenna Television system (usually large apartment blocks, hotels etc) will require a qualified antenna installer to locate and rectify any issues. Finally, a corroded antenna is a potent source of trouble, so any old antenna should be replaced as a matter of course. Antenna installers You need to be careful when accepting the advice of an antenna installer. siliconchip.com.au They may not have kept up with recent changes and you could end up with an inappropriate antenna based on what they have used in the past. For example, there are still people installing the large and expensive antennas required for analog channel 2 – despite the fact that the last channel 2 signal was switched off in December 2013! Antenna installers are not required to have any training in antenna selection and unfortunately the endorsement scheme used in Australia has been dismantled by the Department of Communications. There is a new version of the Australian Standard AS1417-2014 Receiving Antennas for Radio and Television in the VHF and UHF band due to be published soon but there is no compulsion for the industry to use it. As a consequence you are on your own when selecting a qualified installer. SUITABLE TV ANTENNA DESIGNS These diagrams will help you identify the various types of TV antenna discussed in the article. The difference between the antennas for a particular polarisation is the element length and spacing which in turn is determined by the frequency or channel number STRONG SIGNAL AREA: AREA: Dark Green on http://myswitch.digitalready.gov.au/ Antenna suppliers Antenna manufacturers and importers also have an important role to play. They need to supply the industry with antennas designed for the unique technical characteristics of the Australian and New Zealand market. This will reduce the chance of an installer using an inappropriate antenna. This means that suppliers should: • Not sell antennas designed to receive any channel lower than channel 6 or higher than channel 51 (European channel 48). • Discontinue VHF/UHF combination antennas or cross polarised antennas (by the end of this year all transmitters on a site will have the same polarisation). • Not sell UHF log periodic antennas. Most of these are not required because of their wide frequency range and lack of sensitivity. As a minimum, any antenna designed for block E should contain a 698MHz low pass filter in the balun box. Marine and caravan antennas as well as amplified indoor antennas need to have 174-230 and 526-694MHz filters installed internally between the antenna and the amplifier. Existing broadband antennas typically quoted as being able to receiving channels 0- 69 will produce unreliable reception and could cost much more than the right antenna for your area. siliconchip.com.au   Total Dipole length (mm) Gain (dbi) Horizontal Polarisation Vertical Polarisation Block A 740 Block B 273 Block C 254 Block D 237 Block E 222 7 Yagi 10 Yagi 10 Yagi 11 Yagi 11 Yagi Phased Array Phased Array Phased Array Phased Array Phased Array MEDIUM SIGNAL AREA: Light Green on http://myswitch.digitalready.gov.au/ Block A Block B Block C Block D Block E Total Dipole length (mm) Gain (dbi) Horizontal Polarisation Vertical Polarisation 740 273 254 237 222 8 Yagi 11 Yagi 11 Yagi 12 Yagi 12 Yagi Phased Array Phased Array Phased Array Phased Array Phased Array FRINGE AREA: Orange on http://myswitch.digitalready.gov.au/ Block A Block B Block C Block D Total Dipole length (mm) Gain (dBi) Horizontal Polarisation Vertical Polarisation 740 273 254 237 Block E 222 >10 Phased Array Yagi >13 Phased Array Yagi >13 Phased Array Yagi >14 Phased Array Yagi >14 Phased Array Yagi Exceptions to above table: • Gosford NSW and Gold Coast Qld requires blocks D and E to be horizontally polarised. • Bouddi and Wyong NSW require blocks D and E to be vertically polarised. • Currumbin and Gold Coast Southern Hinterland Qld require a unique antenna for channels 34, 35, 36, 37, 38, 39, 49, 50 with vertical polarisation. • Remote area towns (excluding WA) receiving Imparja and Southern Cross Television from a local transmitter generally require a Block A antenna for the ABC transmitter out of town and another antenna pointed in town in a different channel block. A UHF/ VHF diplexer can connect the antenna cables together to feed the receiver. SC November 2014  89