Wireless Waffle - A whole spectrum of radio related rubbish

NOW Wireless Broadbandsignal strength
Tuesday 28 February, 2006, 10:39 - Radio Randomness
Wandering past a local bus-stop, I was intrigued by an advertising poster which shouted, "wireless broadband with no strings attached". Like many people, I have a wireless broadband network at home, however this ad seemed to be offering something different i.e. a broadband connection to the home which didn't rely on wires. Now I know that with a 3G mobile data card you can get a reasonably broadband (circa 256 kbps) connection, but the implication of the poster was that what was on offer was more akin to the services offered by wired broadband.

nowA bit of digging later, I discovered that the service being advertised was one offered by NOW and was indeed a true wire-free broadband to the home connection (so called Broadband Fixed Wireless Access or BFWA). NOW is a trade name for UK Broadband which in turn is a division of pccwPacific Century CyberWorks (PCCW), a Hong Kong based company who also offer BFWA services over the whole of the island of Hong Kong too. UK Broadband won 13 of the 15 regional 3.4 GHz licences available through Ofcom's auction during 2003, securing them 2 x 20 MHz of spectrum (3480 - 3500 MHz paired with 3580 - 3600 MHz). They later bought up one of the other bidding companies giving them 14 of the 15 licences and virtually nationwide coverage.

wirelessbroadbandUK Broadband uses TD-CDMA technology from IPWireless. TD-CDMA is a 3G technology and is part of the UMTS stable. This is in contrast to PCCW's network in Hong Kong which is based on WiMAX. In some ways the choice of this technology is odd, partly from a commercial stand-point as there would have been obvious economies of scale if the company had used the same technology in all its markets; but also because the spectrum they won is paired, making it suitable for frequency division duplex (FDD) technologies, rather than the time division duplex (TDD) technology they have settled on. At the end of the day, financial decisions usually outweigh technology ones so there must have been a commercial imperative for this choice. An alternative line of thought is that as TDD technology can dynamically assign capacity to uplink or downlink as required, and given the asymetric use of bandwidth which internet browsing generates, TDD is actually more spectrally efficient (and economically efficient with it).

It will be interesting to see how successful NOW becomes. Various companies have tried to deliver wireless broadband to the home in the past (including cable giant ntl:) but have always found that the cost of the equipment and specialist installation was prohibitive to competition with fixed line solutions. The NOW service doesn't seem to require specialist installation which is a plus, however presumably the equipment is still expensive compared to the now almost ubiquitous ADSL modem.
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Save Our Set-Top Boxsignal strength
Wednesday 15 February, 2006, 13:26 - Radio Randomness
saveoursettopboxI read an article in The Times newspaper yesterday entitled 'Coastguard scrambled as set-top box sends SOS'. It would appear that, on two separate occasions, radio emissions from a Freeview set-top box had raised an alert with the coastguard who had sent search and rescue helicopters out to find the source, apparently costing GBP20,000 or so on each occasion (special 'centrifrugal' helicopter fuel is very expensive you see).

The alert concerned was simply a transmission on a frequency of 121.5 MHz, one of the internationally recognised distress frequencies. Devices called Emergency Position-Indicating Rescue Beacons (EPIRBs) use this, and other frequencies (406.1 MHz for civil and 243.0 MHz for military emergencies) to alert an international network of Search and Rescue satellites (SAR-SATs) when a vessel is in distress. The various satellites which monitor this frequency can pin-point to within an accuracy of about 20km, the location of any transmission, over an area comprising about 60% of the surface of the earth. The unintentional radiation from the set-top box would therefore have triggered the satellites (which believed it was a distress beacon) to alert ground stations to the signal. The fact that the set-top box concerned was located in Plymouth, a busy naval town as opposed to in the middle of the English countryside would have further alarmed the coastguard (as boats in distress surrounded by miles of farmland would be rather suspicious).

trackdownradiousersThe story continues to say that officials tracked down the source of the interference and knocked, antennas in hand, on the door of the poor unsuspecting lady whose box was at fault. She clearly thought she had been tracked down for television licence evasion, though why she would think this if she had a licence is rather confusing. Obviously the signals were strong enough to merit intervention from the authorities, who took the action of tracking and closing down the problem rather than allowing it to continue.

Two things are surprising about this story. Firstly, the fact that the transmissions from the set-top box were strong enough to raise the alert with the satellite network. EPIRBs operating on 121.5 MHz typically use a power of 50mW or more. The malfunction of the set-top box must have caused some device within the box to oscillate and these oscillations were then radiated back through the TV antenna or the down-lead. To get a 50mW signal in such circumstances, however, is pretty good going. Even a well designed VHF oscillator would struggle to provide a stable 50mW of power on a fixed frequency without drifting as the oscillator got warmer or cooler. And given the poor performance of the antenna at these frequencies, it is likely that the power generated by the set-top box would need to be significantly more than this. It is no surprise that a ground-based search was also able to track down the signal! concordeIt is worrying in many ways that this is the case. Had the transmission been on a different frequency (for example 121.9 MHz) it would have interfered with air-traffic control (in this case at Heathrow airport). Such events do regularly occur, however there are no satellites that can pin-point the location of the transmission and many go unchecked.

The second thing which is surprising is that the box could produce such radiations in the first place. All electronic equipment has to conform to a set of standards known (in Europe) as the EMC directive. This requires all manufacturers to certify that their equipment does not suffer when in the presence of nearby radio transmissions AND that it does not cause unintentional radiation. The set-top box would have had to conform to this standard and thus should have been checked for emissions. Clearly, in this case, the set-top box was malfunctioning, which means that the tests conducted by manufacturers are not extensive enough to capture the results of fault conditions. Does that mean that I could produce a toaster which, if held upside down radiated a couple of Watts in the FM band and claim it conformed when used normally, to toast bread?

What's most worrying is that there are probably hundreds more cases of such radiation which go on unnoticed. In one respect the fact that they are unnoticed means that they are not causing anyone any problems. On the other, it does question whether opening up the use of the radio spectrum in a less controlled manner would really cause the mass devastation that many people seem to think it would.
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Telling Bonesignal strength
Thursday 2 February, 2006, 21:28 - Radio Randomness
santababyNo doubt a lot of people received cordless phones in their Christmas stocking, not least because with cellular phones all the fashion, it seems rather restrictive to have to use a fixed phone at home. Cordless phones come in many flavours, but in particular come in analogue and digital varieties. It's not always that simple to identify, however, which phone is which. In the radio sense, an analogue phone is one which uses analogue modulation (usually FM) to carry the audio to and from the phone. Conversely, a digital phone is one which uses digital modulation. However some unscrupulous retailers who believe that the 'digital' tag is something which sells, often call phones with digital answerphones (i.e. that record messages digitally) as 'digital cordless phones' - they aren't!

Why does all this matter? Well, only true digital phones offer any level of security over eavesdropping on your calls. Analogue phones are as very easy to tune into (more of which later...) I know of people who have bought 'digital cordless phones' in the belief that their calls were secure. A brief demonstration using a portable receiver as to how easy it is to overhear their calls sent them rushing back to the retailer from who they purchased the phone. Would the retailer swap it for a proper digital phone - not without them paying an additional fee (It's true to say that true digital phones still command a slight margin over analogue phones).

dectphonesSo how do you know whether the cordless phone you have is digital or not? Well, firstly if it is clearly marked as a 'DECT' phone (usually shown as the letters 'DECT', standing for Digital Enhanced Cordless Telephony, inside an oval shaped blob) then you're fine. As well as being digital, DECT, a European standard, normally operates at frequencies between 1880 and 1900 MHz which means that signals don't tend to travel far outside the house. There is an equivalent American DECT standard known as DCT-U and alternative American digital standards, all operating around 900 MHz.

For a practical test, try holding your phone next to an electrically noisy device such as a food blender, electric drill or lift/elevator motor. If you can hear crackles or whooshes over the top of your call, chances are you are using an analogue phone.

In the UK, there are three bands in which analogue cordless telephones, termed CT0 - cordless telephony 0 - to represent the '0th' generation of technology - can legally operate (phones imported from other European countries or outside Europe may operate in different bands).

The first of these bands, specified in UK standard MPT 1322 has a base transmitter on frequencies between 1.642 and 1.782 MHz, just off the end of the medium-wave broadcast band, paired with handset transmitters on frequencies between 47.44375 and 47.54375 MHz with a maximum radiated power of 10mW (erp). They can be identified as the base unit has a wire, up to 3 metres long, which trails out of the back. Using such a low frequency, the base transmitters can radiate over quite some distance. These phones are being phased out in preference to the band identified below, but a tune over the lower frequency band will usually yield a number of units still in operation. The handsets, being low power and with small antennas, tend not to radiate over such a wide area.

In 1996 the Radiocommunications Agency, then responsible for managing the radio spectrum in the UK, realised the need for additional channels for analogue cordless telephony to relieve the congestion that was occuring in the existing bands. A further 8 channels were released (specification MPT 1384) with base units transmitting in the range 31.0375 to 31.2125 MHz, and handsets in the range 39.9375 to 40.1125 MHz again at a power of 10mW (erp). Ranges for the base transmitters vary but can extend to over a km.

listeninOne final range of frequencies is used for long range cordless phones (complying with UK standard MPT 1371) with only two channels available and a maximum radiated power of 100mW (erp). Base units transmit on either 47.43125 or 47.41875 MHz and handsets on 77.5125 or 77.5500 MHz.

If you have a receiver that tunes across the range of frequencies used by these analogue phones, particularly those used by the base units, have a listen (though obviously I haven't told you to do this as doing so would force you to break the law and I can't possibly condone that kind of thing). It's amazing what range 10mW can give at some of these frequencies. Far be it for me to suggest that you could make a game out of guessing which of your neighbours regularly visits a 'medium', or which one's son has just come out as or which has insurmountable debts or ...! And remember, if you buy a cordless phone for yourself, make sure it's digital!
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UK CB Radio: Past, Present and Future?signal strength
Tuesday 3 January, 2006, 16:50 - Radio Randomness
Citizens' Band (CB) Radio began in the UK in the late 1970's when truckers and a few other enthusiasts (illegally) imported CB radios from the USA where they were widely available and relatively low cost.

cobra148Prices for these illegal AM sets in the UK were typically around GBP50 which wasn't totally out of reach of even a few school kids. I fondly remember communicating via CB with many of a my school friends whose parents would surely have been worried if they'd known the penalties for operating the equipment!

Under immense populist pressure, the UK government finally relented and on 2 November 1981 the Radiocommunication Agency licensed CB radio of two flavours. CB in America (and in most other countries which had licensed it) operated on 40 channels spread out between 26.965 and 27.405 MHz. The UK decided that, as CB radio was meant to be a local communications service, it would license a different set of channels to stop UK 'breakers' from chatting to overseas CBers when conditions permitted - thus 40 channels from 27.60125 to 27.99125 were licenced with a maximum power of 4 watts and a maximum antenna size of 1.5 metres and height of 10 metres above the ground (these antenna restrictions have since been relaxed). Equipment (marked 'CB 27/81') for the band was readily available from day one at prices similar to the illigaly available US equipment.

In addition to the 27 MHz channels, an additional 20 channels were licensed in the frequency range 934.0125 - 934.9625 MHz. The 934 MHz band was mainly for enthusiasts as equipment was relatively cutting edge and hence expensive and operation required a great deal of skill. A licence fee of GBP10 per year (now GBP15) was payable to use either (or both) bands, though many users, having been used to operating illegally, never bothered with this formailty.

In 1988 the Radiocommunications Agency succumbed to pressure from Europe and licensed the US 27 MHz channels (which had been formally adopted by CEPT for use across Europe). At the same time the withdrawal of the 934 MHz band (at the end of 1998) was announced to make way for GSM phones, and the use of the original UK-only 27 MHz channels was frozen with no new equipment allowed to be manufactured in favour of the CEPT channels.

dukesofhazzardWith the ready availability of equipment and the boosted awareness of CB amongst the general population through films such as 'Convoy' and 'Smokey and the Bandit' and TV shows such as 'The Dukes of Hazzard', the CB channels quickly became the playground for every kind of nutter you could imagine. Many channels were filled with the likes of frustrated DJ's who would spend hours playing music from their bedrooms and people who thought that swearing incessantly on the calling channel represented sport. Towards the end of the 1980's CB usage began to wane and today, even in a highly populated area such as London a tune across the 40 UK and 40 CEPT CB channels yields very little usage. Also, 27 MHz is not an ideal frequency for local communications. At certain times of the year, especially in the summer, propagation allows communication over 1000's of km and channels become clogged as it becomes easier to talk to breakers from faraway places such as Italy and Russia than to talk to people only a few km away.

So is CB radio dead? Well in its original format, possibly. The new UK regulator, Ofcom, has allowed an experiment called the 'Community Audio Distribution System (CADS)' in the 27 MHz band to try and make use of these otherwise empty channels. Meanwhile, in April 1999, Ofcom de-regulated a set of frequencies in the range 446.00625 to 446.09375 for a service called 'PMR446'. PMR446 was a replacement for the previous 'Short Range Business Radio (SRBR)' service which allowed the use of 3 channels at 461 MHz at low power for just GBP30 per annum and was intended to be used by businesses whose radio requirements did not merit a wider-area licence (such as between shop assistants in department stores). However, being licence-exempt, the PMR446 service soon found favour amongst a variety of radio users who might otherwise have used CB. Eight channels are available and equipment is restricted to 500 mW of power and integral antennas, however reliable ranges of around 1km are common.

pmr446Thus those who want to use radio for non-commercial use such as families and event organisers have access to channels which are largely, though not exclusively, idiot-free and that do not suffer from frequent continental interference. PMR446 is an analogue service, however having regocnised its potential, a digital version of PMR446 which should supposedly offer greater range and better audio quality is already on the cards.

Where does this leave CB then? With 27 MHz mostly dead and most 'community' use of radio now using the short-range PMR446 service, there is still a need for a wider area CB type service to replicate the service offered by CB for businesses such as taxi's and logistics companies. Help may be at hand in the form of the little recognised 'UK General' licence. This allows the use of a number of VHF and UHF frequencies with 5 Watts of power (10 times more than PMR 446), however a licence fee of GBP60 every 3 years is payable. The frequencies which can be used are:

77.6875 MHz
86.3375 MHz
86.3500 MHz
86.3625 MHz
86.3750 MHz
164.0500 MHz
164.0625 MHz
169.0875 MHz
169.3125 MHz
173.0625 MHz
173.0875 MHz
173.0500 MHz
449.3125 MHz
449.4000 MHz
449.4750 MHz

A quick scan of this odd collection of channels in West London shows that many are relatively unoccupied and would offer great potential for a supplemental service to PMR446. A more sensible pricing regime for the use of these frequencies (say GBP15 per annum...) or indeed the inclusion of these channels in the UK CB licence might just tip the balance back in favour of CB radio as a sensible solution to the radio needs of small businesses.
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