Wireless Waffle - A whole spectrum of radio related rubbish
Adjø FM Radiosignal strength
Tuesday 28 April, 2015, 15:58 - Broadcasting, Licensed, Spectrum Management
Posted by Administrator
norway wave goodbyeThe Norwegian Communications Authority (NKOM) recently announced that FM radio is to be closed-down in Norway by the end of 2017. The closure will begin at the north of the country, and spread southwards. National broadcaster NRK will wave goodbye to FM radio first, followed by major commercial broadcasters. Some smaller, local broadcasters, will be allowed to continue broadcasting on FM but the rest will continue only on DAB or on other digital platforms (such as television or online).

The switch-over in Norway, follows a similar logic as that used by Ofcom in the UK (as previously discussed by Wireless Waffle). There are a number of specific criteria that the Norwegian government said had to be met for the switch-off to occur:
  • NRK's digital services have to have the same coverage as their FM service, and national commercial services need to cover 90% of the country.
  • There has to be an affordable solution for listening in cars.
  • At least 50% of listeners have to be listening to digital radio every day.
The regulator claims that these targets have been met but broadcaster claim that they haven't. The Norwegian Local Radio Association claims that only 19% of listeners use DAB and that other 'digital' listening is through other platforms. They also argue that an 'all digital Norway' would mean that any tourists driving from a neighbouring country who don't have a DAB radio would be unable to receive local traffic and weather information and that this could prove dangerous. Of course, if those tourists hired a car in Norway, presumably this problem would not occur.

radio snowBroadcasters also fear that driving people away from FM onto, for example, online radio would open up a much wider world of competition from the likes of Spotify. In this respect, FM radio represents a way of limiting listener choice and reducing competition so it is perhaps no wonder that broadcasters are keen to ensure the longevity of the medium.

Norway was one of the first countries to complete the switch from analogue to digital television and is no doubt hoping that it's bold decision to close FM radio will give it similar kudos. However there were good reasons for a digital television switch-over, including the greater choice and higher quality recption that digital offered and, perhaps most importantly from the perspective of the regulator and government, the ability to free up some radio spectrum which could then be sold of to mobile operators for lots of money. Wireless Waffle estimates that the sale of the digital dividend spectrum in the auction that took place in 2013 raised around GBP75 million, which is not that much compared to the very large prices paid in other countries.

nkom trailblazingThe FM band is a different proposition though, because other than for radio broadcasting, there are no other (harmonised) uses for the band. It could be used for mobile radio (e.g. walkie talkies) but there aren't any available that operate in that frequency range. It could be used to extend the aeronautical band (which begins at 108 MHz). It could be used for some, as yet uninvented wireless service. But unless neighbouring countries (and the local FM broadcasters in Norway who continue to use the band) also switch off their transmitters, the levels of interference from these stations would be too high to make the spectrum of any real value.

So what is the real benefit of switching to digital? For Norway, perhaps, a chance to be a trailblazer. For any other country, perhaps none at all.
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Polar Foil - virtually not antennas at all?signal strength
Wednesday 1 April, 2015, 11:01 - Spectrum Management
Posted by Administrator
It is almost a law of physics, that the best way to increase the coverage of a transmitter is not simply to turn up the power, but better still to increase the height of the transmitting antenna. Wireless Waffle has discussed the relationship between height, power and coverage before. It is, however, almost a law of nature, that increasing the height of an antenna through building a taller mast will incur the wrath of residents and environmental protestors and as such, there is a political limit to just how high antennas can be mounted.

birds antennaWouldn't it be great if someone invented invisible, or nearly invisible antennas? One option might be to use atom thin superconducting graphene tubes that were self-supporting but so thin as to be virtually invisible. The only downside of such an antenna would be that any bird that flew into it would be immediately sliced in two as the antenna would have almost infinitely sharp edges.

Another option could be to use multiple beams to project and focus energy at a specific point to materialise a virtual antenna. If force (thrust) can be generated by electromagnetic waves in an EmDrive, then could a similar principal be used to project an antenna at a point away from the source of the physical beams? This far-fetched idea is being considered by Professor Nisan Sakasi at the Communications and Spectrum Management Research Centre at the University of Bilkent, in Turkey.

By focussing very narrow microwave beams which cross in a specific quadrifilar pattern, the air atoms at that point can be ionised to become electrically conductive and with careful tuning,quadrifilar radiation can project a virtual antenna at a point separated from the microwave transmitters by several metres. Professor Sakasi has called the antennas 'polar foil', because the area where the virtual antenna is formed, if viewed from polar angles, glints a little like aluminium foil. Of course at night they are completely invisible.

The difficulty for the team at Bilkent is now to find a way of feeding the polar foil with RF energy so that it can actually radiate useful signals. The team believe that with the right beamforming, a 'virtual feeder' could also be created permitting injection of RF signals from a lower point. A secondary problem is that the amount of electricity needed to feed the microwave transmitters which generate the polar foil is 'in the region of kiloWatts', meaning that the power required to form the virtual antennas is currently far more than that required to generate the radio signals that would feed into them.

The advantages of such a system is that, with tighter beamforming, it may be possible to generate the polar foil not just metres away from the microwave transmitters but tens of metres away. As such, antennas could be virtualised far above the ground, without the need to build masts at all. The fact that the antennas are virtual, and not real, means that problems like slicing a bird in half as it flies into the antenna are virtually unreal and thus no damage would be caused.

A spokesperson for the Royal Society for the Protection of Birds, told Wireless Waffle that:
We are very concerned about the idea of superconducting graphene antennas being erected across the country, however we think that many birds would like the idea of a network of virtual feeders!

polar foil beams
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Nuff sed...?signal strength
Friday 27 February, 2015, 15:09 - Spectrum Management, Much Ado About Nothing
Posted by Administrator
Experts at the University of Surrey have allegedly achieved wireless data transfer speeds of 1Tbps (Terabits per second), albeit in laboratory conditions and over a distance of just 100 metres. Sizzle! Then again, just imagine the cost of rolling out the 10 million or so cell sites that would be needed to cover the UK. Ow! Nonetheless this is a significant achievement. Yay!

1tbps zoom zoom

Mobile data connections working this fast would be able to transfer the contents of a blu-ray disk (typically 50 GigaBytes) in just under half a second. Wow! At typical current average mobile internet tariffs, the cost of transferring the data for the blu-ray would be around GBP200. Wowzer! Assuming you wanted to do this every day, the monthly cost of your mobile contract would be around GBP6000. Zowee!

Do we really need to say any more?
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Martian radio amateurs appeal spectrum allocation decisionsignal strength
Thursday 22 January, 2015, 10:48 - Amateur Radio, Broadcasting, Licensed, Radio Randomness, Spectrum Management
Posted by Administrator
Radio amateurs with designs on operating from the planet Mars are appealing against a decision by the Consultative Committee for Space Data Systems (CCSDS) to allocate the 70 cm amateur band (430 - 440 MHz +/-) for communications between satellites in orbit around the red planet and the numerous rovers that criss-cross its surface.

In a statement, released by the Mars United People for Planetary and Earth Transmissions (MUPPETs), tea-drinking general secretary Arthur Dent said,
MUPPETs have been planning a DX-pedition to Mars for some time. To discover that our officially allocated radio frequencies are already in use is just not fair. It constrains our ability to talk about radio stuff to each other and means other radio amateurs around the solar-system will be denied extra points in the forthcoming 'talking about radio stuff with other radio nuts' contest.

Responding to the accusations, Prostetnic Vogon Jeltz of the CCSDS commented,
prostetnic jeltzThe 70cm frequency band has been used for communications on and off Mars since the Viking lander first set foot on the planet back in 1976. The MUPPETs have had plenty of time to comment. The plans for frequency use on Mars have been available at the local planning office on Alpha Century for fifty of your Earth years, so they've had plenty of time to lodge any formal complaints and it's far too late to start making a fuss about it now. I'm sorry but if they can't be bothered to take an interest in local affairs that's their own regard.

Appallingly obvious references to the Hitch-Hikers Guide to the Galaxy aside, it may surprise many people to learn that there is, indeed, a frequency plan for Mars. And that there are already 5 communication satellites in orbit around the planet! For communication from the rovers on the surface to the orbiting satellites, frequencies in the range 390 to 405 MHz are used. For the link down from the orbiters to the rovers, the frequency range 435 - 450 MHz is used, which falls inside the amateur radio 70cm band.

The choice of the particular frequencies in use (on Mars) is designed to try and stop anyone deliberately causing interference from the Earth, whilst retaining ease of use on Mars (i.e. the ability to use omni-directional antennas). The various satellites orbiting Mars typically get no nearer than around 400 km from the surface and communication with rovers typically takes place when the satellites make their closest pass. The shortest distance between the Earth and Mars is typically around 60 million km. The table below shows the path-loss at 415 MHz of these distances.

Route Distance Path Loss
Satellite to Mars surface 400 km 137 dB
Earth to Mars 60,000,000 km 240 dB

So the difference in path loss is just over 100 dB. For a transmitter to cause interference from the Earth to communication on Mars, it would therefore have to have a radiated transmitter power 100 dB higher than the signals passing between the rovers and the satellites.

mars uhfA very good description of the communications with Mars is provided by Steven Gordon (from whom the diagram on the left is shamelessly plagiarised). The transmitter power used on Mars is 5 Watts (7 dBW), so in order to cause interference from Earth, a transmitter power of around 107 dBW, or 50,000,000,000 Watts (a.k.a. 50 GigaWatts) would be required. Would it be possible to generate such a signal?

Firstly, it ought to be possible to generate at least 100,000 Watts (100 kiloWatts or 50 dBW) of power at the necessary frequencies as television transmitters for the UHF band that reach this level are available. So what is then required is an antenna with a gain of 57 dB. This requires a dish with a diameter of around 150 metres. The largest dish antenna in the world is the radio telescope at Arecibo, Puerto Rico, which is 305 metres in diameter.

muppets cq dxIf a high powered television transmitter was therefore connected up to the Arecibo radio telescope antenna, it ought to be more than possible to jam the transmissions between the Mars rovers and the orbiting satellites during periods where the Earth and Mars were closely aligned. Of course this kind of power level is way beyond the normal licensing conditions of a typical radio amateur and the right conditions would occur roughly every 2 to 3 years when the Earth and Mars come closer together. Nonetheless, commenting on this finding, Arthur Dent of the MUPPETs jeered,
Safe from interference, eh? Who looks silly now then Jeltz!

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