Wireless Waffle - A whole spectrum of radio related rubbish
Come fly with me...signal strength
Saturday 31 August, 2013, 15:07 - Spectrum Management
Posted by Administrator
sexy stewardessAccording to an article in the Daily Mail, a funeral taking place in Windsor, direcly under the flightpath for aircraft landing at London Heathrow airport was interrupted by the voice of a stewardess coming over the church's public address PA system saying, "fasten your seatbelts", and, "prepare the doors for landing".

The article claims that this occured because the 'church's wireless microphone and the plane's radio were on the same frequency'. Radio microphones in the UK operate in a variety of frequency bands. Most commonly they operated between 173.1 to 175 MHz and 863 to 865 MHz, both of which are available on a licence-exempt basis for such purposes. There are other frequencies available but these are subject to the need for a licence and are only normally used for professional programme making and special event (PMSE) uses. Most domestic and everyday business use (including local DJs, schools, hotels and churches) use the licence-exempt channels.

So how could the church's radio microphone be operating on the same frequency as an aircraft? If this is true, there are two possibilities:
  1. The systems on-board the aircraft used the same licence-exempt frequencies that the church's radio microphone used. Or
  2. The radio microphone system being used by the church was not on the officially sanctioned frequencies but was operating on frequencies reserved for aeronautical communications.
Looking at the first possibility, in general the PA systems used on aircraft are not wireless. Aircraft manufacturers, as a rule, try and minimise the amount of electromagnetic energy flying around the inside of their planes to try and ensure that the sensitive navigation systems are not interfered with (this is the reason that electronic devices, especially mobile phones, have to be switched off for take-off and landing). That being said, the European reference document on licence-exempt frequency usage (ERC Recommendation 70-03) states:
The CEPT has considered the use of short-range devices on board aircraft and it has concluded that, from the regulatory perspective, such use is allowed under the same conditions provided in the relevant Annex of Recommendation 70-03. For aviation safety aspects, the CEPT is not the right body to address this matter which remains the responsibility of aircraft manufacturers or aircraft owners who should consult with the relevant national or regional aviation bodies before the installation and use of such devices on board aircraft.

So it would not be illegal for an aircraft manufacturer to use licence-exempt wireless microphones on-board their planes. There is also increasing interest in using wireless technology to control the actual flight of the aircraft (the ailerons, flap, engines and so on). Planes using 'fly-by-wireless' technology have already been tested and there are now moves to try and find dedicated spectrum for them to operate in. This negates the need for the usual wiring that is required and saves weight which in turn saves fuel and cost.

illegal radio microphoneLooking at the second possibility, there are radio microphones on the market which operate in the aeronautical communications (VHF) band from 108 to 137 MHz. These devices, commonly imported from China, are available on internet outlets at very low cost (check the frequency range on this microphone for example). They are, of course, completely illegal to use and not only are they subject to the kind of interference from aircraft that would have caused the problem in our church above, but they also have the potential to cause interference to air-to-ground aircraft communications which is stupid and potentially life-threatening. However despite such devices being available, this scenario is much less likely because the stewardess's voice would not be transmitted on the air-to-ground communication frequencies which are for pilot and air traffic controller communications only.

So it seems that it was probably the use of licence-excempt frequencies for short-range audio communications on-board the aircraft that was the culprit. It's worth considering that interference is usually bi-directional, especially where the systems are using similar powers and modulation. So it is just as likely that passengers on-board the aircraft could have been subject to the eulogy being given from the church as vice versa.

Which opens up a completely legal but very naughty set of ruses that anyone with suitable equipment could carry out if particularly bored on, say, a Sunday afternoon. Just stand near the end of the runway at an airport with a completely legal radio microphone operating, most likely, on the 863 to 865 MHz band and pick yourself a channel. As each aircraft comes overhead shout 'Brace, brace, brace' and if the aircraft's on-board wireless audio system happens to be on the same channel as your microphone the passengers are going to go ape. Of course, Wireless Waffle would never condone such activity, but if aircraft manufacturers are going to use licence-exempt frequencies, which are subject to no protection from interference, for on-board communications they are opening themselves up to all manner of prankery. If they choose to use bluetooth to actually control the aircraft itself, heavens only knows what might happen. Perhaps it would be best to stick to using wires or even optic fibre for controlling aircraft.

shouting at aircraft
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Strewth! Aussie 700 MHz auction comes a guster!signal strength
Tuesday 7 May, 2013, 08:14 - Spectrum Management
Posted by Administrator
brass in pocketThe Aussie auction of 700 MHz spectrum (one of the first of it's kind in the world) has, on the one hand, left the Australian government a few cents short of a brass razoo but at the same time left operators paying big bikkies for the spectrum. Wireless Waffle has previously discussed who the winner of the UK spectrum auction actually was. Whilst the UK auction (and most others around the world) are for 800 MHz spectrum, the Australian auction is relatively unique in that it is for 700 MHz spectrum. The auction has left a third of the available 700 MHz unsold, which is not a good place to be as: (a) the spectrum is not being used, which is clearly inefficient, and (b) it means it will have to be re-auctioned, which means a bit more hard yakka for the Australian regulator ACMA.

The fact that spectrum could remain unsold had been predicted by some, as a result of having set the reserve price too high. So just how does the price paid in the Australian auction compare to that paid elsewhere? The table below sets out the prices paid for 800 MHz spectrum in Germany, France, Italy and the UK and compares this to the price paid for 700 MHz spectrum in Australia. The comparison made is on a 'price per MHz per population' basis and for fun, GDP (PPP) has been factored in to see whether this makes any odds. Prices are all converted to Euro.
Country Band Euro per MHz per pop Euro per MHz per pop
(GDP adjusted)
Germany 800 MHz 0.73 0.68
France 800 MHz 0.69 0.71
Italy 800 MHz 0.83 0.98
United Kingdom 800 MHz 0.51 0.52
Australia 700 MHz 1.06 0.92

What does this tell us? Other than the fact that it demonstrates an ability of Wireless Waffle to do some simple maths, it shows that the price paid per MHz per person in Australia was almost 40% higher than the average of all these countries put together. Similarly, when scaled for GDP, the price paid is still 20% over the odds. The only more expensive spectrum was that sold in Italy and this is only because Italy's GDP per capita is somewhat smaller.

So why would operators down under be willing to shell out more moolah for spectrum than elsewhere? Perhaps the secret lies in the rapid population growth taking place. Just a few days ago, it was predicted that the Australian population had reached 23 million. But more importantly, the population is predicted to rise to 40 million in around 40 years time representing growth of around 1.5% per year. This is much faster than the population growth in other countries and means that in just 10 years time, the population of Australia will be 15% larger. If you do the price per person calculation now, the €1.06 becomes €0.92 and the €0.92 becomes €0.80. This puts the prices on a GDP adjusted basis just 5% ahead of average. In 15 years time the prices would be 5% below average. So over the life of the licence maybe these prices are not too high. Of course the population of other countries is growing too, and this would have to be factored in to any more detailed comparisons (such as a competent economist might make).

banana vs births

There are statistics to show that the number of bananas imported into the UK is closely correlated with the growth in population (as the above graph clearly demonstrates). It therefore follows, using Spock-strength logic, that there is a connection between bananas and the price differentials paid at auction for spectrum. Australia grows lots of bananas and it's population is rising, and lots was paid at auction. Q.E.D. as they used to say in ancient Rome.

What does this prove? Nothing at all, but having called the European Commission 'nuts' last month, the time was right to make another foodstuff related comment about a regulator somewhere or other. And so it seems (as so obviously can be deduced) ACMA is clearly bananas!

big banana
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Poll: What Should The Radio Spectrum Be Used For?signal strength
Thursday 25 April, 2013, 04:00 - Amateur Radio, Spectrum Management
Posted by Administrator
http   www wirelesswaffle com  keyfob womanOver 5 years ago, Wireless Waffle reported on the fact that a UK radio ham repeater was forced off air to stop interference to licence-exempt 'wireless car unlocking keys' (and no excuses are necessary for re-using the rather fetching graphic one again). In this instance, because radio amateurs are secondary users of the band, and often regarded as second class citizens by regulatory authorities, it was the hams that had to find a solution. The fact that the value of the spectrum used by radio hams is generally rather large, yet they pay little or no licence fees, no doubt increases regulatory lethargy when it comes to lending a hand to deal with these kind of problems.

In the USA, however, the same situation has occurred, but instead of it being radio hams that caused the problem, it was the US military. And instead of it being wireless car keys being interfered with, it was wireless garage door openers. It seems that residents of Savannah (Georgia) have found their wireless garage door openers have stopped operating. The problem is caused by radio base stations at nearby military facilities which have begun operating in the frequency range 380 to 399.9 MHz, which has hitherto been a common band for wireless garage openers.

But unlike in the UK, the US military have stood their ground and said that it's tough luck for anyone who is affected as the spectrum is rightfully theirs. According to US Government Accountability Office report GAO-06-172R:
To address homeland defense needs and comply with government direction that agencies use the electromagnetic spectrum more efficiently, the Department of Defense (DOD) is deploying new Land Mobile Radios to military installations across the country. The new Land Mobile Radios operate in the same frequency range (380 to 399.9 MHz) as many unlicensed low-powered garage door openers, which have operated in this range for years. While DOD has been the authorized user of this spectrum range for several decades, their use of Land Mobile Radios between 380 and 399.9 MHz is relatively new. With DOD's deployment of the new radios and increased use of the 380-399.9 MHz range of spectrum, some users of garage door openers have experienced varying levels of inoperability that has been attributed to interference caused by the new radios. Nevertheless, because garage door openers operate as unlicensed devices, they must accept any interference from authorized spectrum users.

Yay! A big thumbs up for common sense, or at least from a spectrum management perspective that's what it is. But most legal cases use the 'reasonable person' principal. This basically asks the question, 'What would a reasonable person regard as the correct solution?' So... Is it reasonable that the military should be able to use radio spectrum that is rightfully theirs to defend the country, or is it more important to allow people to be able to open their garage doors without getting out of their cars? In this case, the reasonable person (even if that person happened to be the owner of a wireless garage door opener) would probably cede that the military boys have a point.

Now ask the same question for radio hams... Is it reasonable that radio hams should be able to use radio spectrum that is rightfully theirs to talk about radio stuff, or is it more important to allow people to be able to unlock their cars without putting their key into them? The answer in this case is less clear. The reason for this is probably to do with the description of who is using the spectrum for what.

Most people would agree that 'defending the country' was of high value compared to general laziness in door opening practises. But 'talking about radio stuff', well that's a different case altogether. Of course radio hams do use their frequencies for emergency communications and organisations such as Raynet would no doubt argue that use of radio ham frequencies is not about 'talking about radio stuff' but is more about providing a 'national voluntary communications service provided for the community'. If every radio ham was a member of an organisation such as Raynet then perhaps this would hold some water, but listen to your local radio ham repeater (you can check out the GB7OK and GB3OK repeaters online). I'd call that 'talking about radio stuff', wouldn't you?

For a bit of fun, below is a poll. Which of the uses of the spectrum do you value most highly? Just select the ones that you think are the most valuable and click 'submit' and the results so far will be displayed to you.


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Eurovision, but no Eurosound?signal strength
Thursday 4 April, 2013, 22:05 - Licensed, Spectrum Management, Chart Predictions
Posted by Administrator
eurovision logoIt is now only a month or so before the annual pan-European musical bun fight that is the Eurovision Song Contest (which is on the 18th of May). The 39 songs that have made it to the competition (which this year is in Malmo, Sweden) are now available to listen to online - with many having professionally produced videos viewable on YouTube. As always there is a mix of complete Euro-nonsense (Greece with their song Alcohol Is Free), songs that could have been written for Eurovision any time from 1960 to the present day (Switzerland's song You And Me falls into this category) copies of last year's winner in the hope that people will want the same thing again this year (Germany's Glorious for example), sickly pop songs with no real substance (Finland's Abbaesque entry Marry Me) and this year, it seems, a whole swathe of rather nice ballads.

For what it's worth, Wireless Waffle is particularly fond of the Icelandic entry (Ég á Líf), the video for which awaits your enjoyment below. If you are of an emotionally sensitive disposition, make sure you have some tissues to hand.



Our selection of songs that ought to be in the top 5, at least if they are able to reproduce the performance in their videos on stage on the night are:
  • Eyþór Ingi Gunnlaugsson - Ég á Líf (Iceland)
  • Roberto Bellarosa - Love Kills (Belgium)
  • Zlata Ognevich - Gravity (Ukraine)
  • Despina Olympiou - An Me Thimáse (Cyprus)
  • Dina Garipova - What If (Russia)
But dodgy songs aside, the contest has always been a real test of ingenuity and resourcefulness for broadcast engineers. Those who remember the show from the early 1990s will recall the 'fun' that took place trying to establish the video feeds from the countries voting, with cheers going up from the audience on occasions when the link was finally made. These days, making a video connection from one place in Europeland to another is comparatively straightforward, though dealing with the presenters egos is a whole different problem.

What has become more complex, though, is the use of wireless technology for the event. Whilst it's still normal in a concert hall to use wired cameras, the use of radiomicrophones and in-ear monitors (which allow the performer to hear themselves sing without the noise of the surrounding environment) has grown significantly over recent years. Figures provided in response to a European Commission consultation on programme making spectrum show an average annual growth of 12% in the number of such devices employed over the past 15 years (but nearly 40% growth per year over the last 4 years).

Year Venue Radiomicrophones used In-Ear Monitors used
1998 Birmingham, UK 40 2
1999 Jerusalem, Israel 42 6
2000 Stockholm, Sweden 48 16
2001 Copenhagen, Denmark 48 16
2002 Tallinn, Estonia 54 16
2003 Riga, Latvia 54 16
2004 Istanbul, Turkey 54 16
2005 Kiev, Ukraine 54 16
2006 Athens, Greece 54 16
2007 Helsinki, Finland 56 16
2008 Belgrade, Serbia 56 16
2009 Moscow, Russia 56 16
2010 Oslo, Norway 72 32
2011 Düsseldorf, Germany 82 40
2012 Baku, Azerbaijan 104 80

What is driving this growth? One the one hand, the equipment costs are coming down making it more affordable to use wireless microphones. On the other, it's also probably true that in earlier years, microphones would be passed from one user to another as they went on/off stage whereas now each artist and band has their own set of equipment which is tailored to their own needs.

radio microphone 1955

Equipment is one thing, but what about the radio spectrum issues? Radiomicrophones and in-ear monitors are normally analogue (for reasons that can wait for another day) and use around 200 kHz of spectrum each. If all the devices in Baku (184) were turned on at the same time, they would need 37 MHz of spectrum just to exist. But this is not the full story. Firstly, if devices were 200 kHz apart, there would be not a sliver of a gap between them. Whilst they could all successfully transmit, even the smartest digital receivers would find it difficult to separate them from each other - and we aren't dealing with digital technology. In reality, frequencies are separated by at least 300 kHz and often more to allow the receivers room to breathe.

The situation is even worse than this however. Due to the close proximity of devices to each other, and of devices to receivers, there is a tendency for lots of intermodulation to occur. If you assume that each 200 kHz channel that can be used is numbered, starting at 1 then you can't use the adjacent channel because it's too close. You also, because of intermodulation, can't use any channel which represents the difference or sum of twice the value of one channel being used minus another channel being used. As and example:
  • If you are using channels 1 and 3 (channel 2 is adjacent to channel 1, so you can't use that), you can't use channel 4 (as its adjacent to 3) or channel 5 (as its 2*3-1). The next available channel is 6.
  • If you are using channels 1, 3 and 6, you now also can't use channel 7 (adj to 6). The next available channel is 8.
  • If you are using channels 1, 3, 6 and 8 you now can't use channels 9 (adj to 8), 10 (2*8-6) or 11 (2*6-1). The next available channel is 12.
... and so on.

The diagram below shows the situation. Green channels are those in use. Red channels are adjacent channels that can't be used. Purple channels are intermodulation products. Pink channels are both at the same time!

radio mic intermod

In the example given above, out of 24 available channels, only 8 are useable. Actually, if you extended the diagram at this point you would find that another 10 channels are already 'wallied out' because of intermodulation. So 8 transmitters has used 34 frequencies! The relationship between the number of transmitters on-air and the number of channels sterilised is not linear but in general something of the order of 1 frequency in 5 can be used for radiomicrophones where they are packed densely in a given location if these problems are to be avoided.

This represents pretty poor frequency efficiency but is fairly representative of what is achieved in real life, which is that only something like one fifth of any spectrum available for radiomicrophones or in-ear monitors can be used in any one venue at the same time. Returning to Baku then, the amount of spectrum required is not 37 MHz, but to support 184 devices simultaneously would require more like 184 MHz of spectrum: give or take 1 MHz per device!

Most radiomicrophones (and in-ear monitors) operate in and amongst television broadcasts in the UHF band which notionally runs from 470 to 862 MHz. In many countries, however, the upper end of this band from 790 MHz upwards has now been set-aside for mobile broadband services, leaving 320 MHz remaining for television broadcasting (and of course radio microphones).

look no wiresAzerbaijan, last year's host of the Eurovision, is yet to switch over to digital TV and equally has not yet used the upper part of the UHF TV band for mobile services and so finding 180 MHz of spectrum for radiomicrophones is presumably not that difficult. In 2013, however, the contest is in Malmo, Sweden. Not only has Sweden cleared the upper part of the UHF band for mobile services, but it has also gone over to digital broadcasting. Malmo is virtually on the border between Sweden and Denmark meaning that the local TV spectrum will be occupied not only by the 8 Swedish multiplexes but by the Danish ones too. Finding 180 MHz of spectrum for this year's competition is therefore much more challenging.

But move forward 10 years and then what will happen. For starters, at the current rate of growth, and assuming no improvement in the spectrum efficiency of wireless microphone technology, there will be a requirement for 560 MHz of spectrum for the Eurovision. Secondly, the parts of the UHF TV band currently unoccupied and used for these purposes will be full of 'cognitive radio' devices hunting out every last vestige of unused spectrum. What will happen then? The simple fact is that no-one really knows, but the programme making community are worried, and understandably so. If there was a way around the intermodulation problem, then the amount of spectrum required would decrease, so perhaps now is the time for some enterprising RF engineer to find a solution to this problem so that we can continue to enjoy the pageantry of the world's greatest song contest. Either that or sing less? Some would argue that for the Eurovision that would be no bad thing.
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