Monday 24 April, 2006, 15:08 - Radio RandomnessThe practice of jamming radio transmissions has been around since radio was first used for military purposes when one side would attempt to inhibit the communications of the other side by transmitting on the same frequency at the same time. Indeed such military jamming is usually termed 'electronic counter-measures' or ECM and a whole industry has developed around it to try and produce radio systems that are resilient to jamming known as 'electronic counter-counter-measures' or ECCM. The picture on the right shows an example of a drone in use today for jamming - in this case one known as a Dragon. The payload of the missile is a high power transmitter which can then be sent to the area of interest and remotely activated. You can see the antenna which unfolds from the front of the device when it is deployed.
However jamming is not strictly a tool of the military. Jamming of broadcast radio stations has been a regular activity for many organisations and - and here's the disappointing bit - continues to take place even today. In the height of the cold war, countries such as Russia used to jam short-wave transmissions from countries such as the UK and USA which carried news or information which the Russians viewed as anti-communist propaganda. To try and compensate, broadcasters such as the BBC World Service, Radio Free Europe and the Voice of America used to transmit their programmes on several short-wave frequencies at the same time (usually 4 or more) in the vain hope that at least one of them would be receiveable in a given area clear of the jammers. The Cuban authorities also jammed Radio Marti, a US Government funded station aimed specifically at the country.
Although they haven't admitted it, China continue to jam Mandarin language short-wave transmissions from the same kinds of stations even today (take a look at this article for example). Tune to the BBC Chinese service (try 9580, 11945, 11980 or 13970 kHz or look at the most recent programme schedule N.B. this page is in Mandarin) and you're likely to hear either the familiar 'wobble' sound over the top of the transmission or 'distorted voices' - both symptoms of a jammed frequency. It's odd that such activities still take place when, with the advent of the internet, the kind of 'propaganda' that the Chinese are trying to guard against is freely available to anyone with a computer. Of course, not all the population of China have access to a computer but with internet cafe's many do (though the Chinese authorities do their best to stop people getting access to such information). There are also case of the Chinese jamming themselves!
Whilst such overt jamming of international stations by such political regimes is virtually taken for granted, there have been deliberate attempts to block transmissions from other stations by apparently respectable regimes. Read the story of Radio Caroline whereby the British Government decided to jam its transmissions to stop them being heard during election times. The British Government pulled another fast trick in 1990 when it licensed a station in London on 558 kHz, the frequency used at the time by Radio Caroline. The choice of frequency was clearly chosen to stop Radio Caroline from being heard in London (though the plan vaguely back-fired as the London station was forced to temporarily simulcast on 990 kHz as the 558 signal was so badly interfered with by Radio Caroline).
More recently there has been a story suggesting that the US Government was deliberately jamming radio communications during the recent disaster in New Orleans. Whilst the US Government clearly could have done more for the residents of this flood-stricken town, it belies belief that they would actively try to scupper rescue attempts.
What is clear is that despite significant developments in radio technologies and in international relations, radio jamming transmitters seem to be as active today as they have always been, mucking up military communications and supressing freedom of speech. Let's hope that one day soon, neither of these uses will continue to be necessary.
Tuesday 18 April, 2006, 15:31The number of radio stations in the UK has been on the increase since commercial radio was first licensed since the late 1970's. The latest raft of licences (excluding the community licences recently awarded) includes stations whose potential audience is, to put it mildly, tiny. The coverage of stations such as TwoLochs FM, LochBroom FM and Isles FM - all of which are in a highly unpopulated area of Northern Scotland - probably does not stretch to more than around 10,000 people. There is an unarguable need for these isolated communities to have local services to bring them together and broadcast radio is a good way of doing this, however one has to wonder whether it is a good use of the radio spectrum or not.
In London for example, radio spectrum is at a premium and despite there already being over 21 FM stations in the city, there is still pressure for more. Could the frequencies that have been assigned to these remote stations not be more effectively employed providing new FM services in London where the audience potential is nearly 1,000 times greater? The answer, sadly, is 'NO'. The distance between these remote stations and London is well over 600 km, so even if all the frequencies on the FM band were assigned to stations broadcasting in Northern Scotland, they could still be re-used in London without causing interference to each other.
The question of whether or not it is a good use of spectrum or not remains valid though. As an example, the programme schedule of TwoLochs FM shows that on a week-day, between 09.00 and 17.00, for a total of 8 hours, the station relays programmes from Prime Time Radio - a service which is available in the same coverage area via Sky Television on channel 0132. Now clearly any small scale radio station has to fill its schedule somehow and the availability of cheap 'filler' services such as this is no doubt a real boon for them, but it's not the local community service that the station was licensed to provide. Would it not be better to provide a local 'juke-box' service played out from a computer hard-drive which could be loaded with requests each week - at least that way the service retains a local feel.
As much as local or community radio initiatives such as this are to be applauded and the hard work of the staff and volunteers who run the station should be appreciated, the question of whether or not they represent an effective use of the radio spectrum remains largely open.
Wednesday 22 March, 2006, 10:16 - LicensedAccording to Isle of Mann International Broadcasting (IOMIB) around 75% of radios have the long wave band on them. But when was the last time you tuned into long wave? For the cricket coverage on BBC Radio 4? Or when Atlantic 252 was pumping out its 'You're never more than a minute away from the next minute' style of upbeat pop music? Other than that, unless you live outside the UK and keep in touch by listening to Radio 4, you probably rarely switch your radio to the 'LW' setting. But there are a number of broadcasters who are banking that they can start commercial services on long wave and get you to tune in to listen to their programmes - and their advertisements!
In the mid 1990's when Atlantic 252 was in its heyday, three other companies figured that they too could launch successful long-wave radio services for the UK. Of the three, two are still planning their launch nearly 10 years later and one has given up. A combination of political, financial and environmental obstacles have prevented any of the three stations from finally getting on-air and a question has to hang over the two who still have plans as to whether they will ever launch.
The aforementioned IOMIB (whose other web-site can be found at longwaveradio.com) plan to launch a service tentively named 'MusicMann279' on 279kHz with a power of 500kW. Their transmitter site was originally planned to be on the mainland of the Isle of Mann, however due to local objections and despite planning to use a Cross-Field Antenna which is much smaller than a conventional antenna (and some would argue that its performance is in proportion to its dimensions), they now plan to build a platform in the Bahama Bank just off the island. There have been various rumours about a possible launch date for the service and plenty of speculation about what kind of service it might be, but so far no real evidence of any progress. There most recent rumours circulating are that the service will launch in the summer of 2006 at reduced power under the name of 'Caroline 279'. I somewhat doubt this latest rumour as there are a couple of aeronautical navigation beacons (non-directional beacons or NDB's), one near RAF Northolt on 277 kHz and one near RAF Lyneham on 282 kHz which are still in operation and in daily use. The interference to these beacons from the proposed Isle of Mann service would be so strong that they would have to change frequency and... they haven't!
The station which has now given up the ghost was known as variously 'Delta 171' or 'The Lounge' and was intended to provide an adult orientated middle-of-the-road, 'BBC Radio 2' style service, broadcasting out of the Netherlands. In the same way as in the Isle of Mann, there were local environmental objections to having a 500kW (half a MegaWatt!) transmitter on the doorstep so Delta was forced to consider a platform in the North Sea. This proved too expensive and the project collapsed in 2000 when the licence for the long wave frequency which had been awarded by the Dutch regulator expired and was not renewed.
The final station which still claims to be planning a launch is 'Cruisin 216' which will carry Christian programming. Cruisin intends to operate out of southern Norway to put its signal into the UK, however the frequency they have of 216 kHz is shared with Radio Monte Carlo (RMC-Info) who use a powerful 1.4 MegaWatt transmitter from Roumoules in south western France. Cruisin's own web-site indicates that their signal in London will be approximately 13dB (20 times) stronger than that from RMC-Info, however the same article on their web-site also shows that this is insufficient for interference not to be a problem. The fact is that the RMC transmitter already puts in a good and listenable signal into London and most of the south eastern corner of England so the signal from Norway would have to be whopping to compete. In Scotland and the north of England they might stand a chance - of course being a religious station, there may be someone up there lending them a helping hand!
Thursday 16 March, 2006, 13:44 - Radio RandomnessWireless LAN's are fabulous things. You put a box next to your cable or ADSL modem with a little aerial on the back and your broadband internet connection miraculously becomes available all over your house to any device fitted with the appropriate wireless card. Or does it...?
In some cases the position of the modem and wireless box are such that coverage does not extend to all points of your house. For example, most incoming telephone (and cable) connections tend to be on an external wall, which by default, is at one end of a property and not in the middle of it. And often they are at floor level, which is where all the modem/wireless equipment also ends up. Now although radio can at times seem magic, putting a wireless box on the floor at one end of your property probably means that upstairs at the other end, the signal is very weak. So what can be done to extend the coverage of wireless LANs?
The first, and easiest thing, is to put the wireless box in a more favourable position. Many can be wall mounted (though this still puts the device at one end of a building), but even raising the position from on the floor to head-height helps. If you have a phone socket or cable connection somewhere else in your house, i.e. in a lounge that might be more central, move the wireless box here and put it on a shelf so it's not at floor level. Putting the box centrally within a property helps even out the signal throughout the building.
If neither of these are possible and the only place where the box can be located is next to the phone socket, is there anything else that can be done to make the signal stronger? The answer is a resounding YES. By far the easiest way to do this is to replace the antenna that comes with your wireless box for one with higher gain. Standard antennas have a gain of 2 dBi - this means that the effective radiated power (erp) of your wireless box is the same as the transmitter power, so if the transmitter is 10 milliWatts (mW), the radiated power will also be 10 mW. Replacing the aerial with one with higher gain increases the radiated power for the same transmitter power and has the added benefit that it improves reception by the wireless box too extending the overall range. Without going into the maths, to double the range of a transmitter, the radiated power has to go up by a factor of 4 (which can also be expressed as 6 dB). So an antenna with a gain of 8 dBi will double the range (or quadruple the coverage) of the system compared to one with 2 dBi gain.
And such antennas are available, and they're not expensive. Visit eBay and do a search for 9dBi and you'll find that for about GBP15 (including postage) there are lots of 9 dBi gain antennas available (remember to make sure that the connector on the bottom of the antenna is the right one for your wireless box - R-SMC are the most common, followed by R-TNC). Replace your standard antenna with one of these high-gainers (which are about 40cm long) and you should find that your coverage has gone up significantly.
Is it legal to do this? Good question! In the UK, Ofcom allows powers up to 100 mW erp . The simple answer is 'it depends'. Most wireless LAN access points have a transmitter power of 100 mW already, so installing a high-gain antenna means the erp will exceed the UK limits. What are the chances of getting caught? That's a different matter...