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...
Thursday 9 March, 2006, 15:24 - Pirate/ClandestineWith all this talk of pirate radio, a question that often gets asked is, "But I've never heard a pirate station; where do I find one?". Yes, there are those who have yet to stumble across the skull and crossbones of the airwaves!
The best place to look is on the FM dial of your radio. But with so many stations around, how do you know if the station you are listening to is a pirate or a legal station? There are a few clues which even the least experience listener should be able to fathom:
1. The signal is in mono. Most pirate stations broadcast in mono, however, this is not at all conclusive as many RSL stations do this too and further, some pirates broadcast in stereo.
2. There is no RDS. Including RDS can be complicated for some pirates so they choose not to use it. This is still not totally conculsive though, as some RSL stations have no RDS either.
3. The RDS is 'scrolling' (i.e. it is changing to display a message - as shown here on the right). Legal stations in Europe are obliged by the European Commission to use a static name on their RDS display to make sure drivers aren't distracted. Pirates, however, can change the name of the station to display messages on RDS equipped radios. A few legal stations (not in the UK though) do scroll or rotate the message on the RDS display so this too isn't totally conclusive, however reading the message might give a good indication. If it's advertising a party at a local night club then chances are you're listening to a local pirate!
4. The presenter doesn't have a middle-class accent! This is especially true on FM stations in the UK, where legal stations try to recruit presenters with unoffensive voices that won't turn listeners off. As pirate stations are usually there to promote the music or club nights, whether the presenter can pronounce 'Douglas St.John Farquhar' correctly really doesn't matter!
5. The phone number being given out to contact the station is a mobile number (all mobile numbers begin with '07' in the UK). How many legal stations do you know who would, or would need to, use a mobile number for calls to the studio? Further, if you're requested to leave 'missed calls', i.e. to phone the number but not let it answer, you're almost certainly onto a pirate. This is a way to show you are listening without having to spend a single penny on phone calls - quite smart really!
Of course there are other clues, such as the frequency being used (if it's in the middle of the band used for national BBC stations but isn't a BBC station then it's most likely a pirate), but the ones above don't require any technical knowledge. You're more likely to find a pirate station on FM if you live in, or near, a major city than if you live out in the countryside, but you might be surprised.
Another place to find pirates is in the radio no man's land just at the edges of the normal short-wave broadcast bands, especially the lower frequency bands. Why the lower frequency bands in particular - they're better for broadcasting to nearby areas and tend to be more reliable throughout the daily propagation cycle. Good places to listen for pirate short-wave stations are:
* 3800-3950 and 4000-4100 kHz, either side of the 75m broadcast band
* 5750-5900 and 6200-6400 kHz, either side of the 49m broadcast band
* 6800-7000 and 7350-7600 kHz, either side of the 41m broadcast band (avoiding the 40m amateur band too)
* 9300-9400 and 9900-10000 kHz, either side of the 31m broadcast band
And so on either side of the other short wave broadcast bands too... Though the use of frequencies above about 10 MHz is rarer, there are examples such as Alfa Lima on 15070 (± a bit) and 21900 (± a bit) kHz and WR International on 12256 kHz.
One final place you might come across a pirate station is on the medium wave (MW) band. Most stations prefer FM for local broadcasting as the antennas are smaller and the equipment easier to get hold of, but a few stations do use MW. Radio Free London used to put out a good signal across London on 819 kHz and there are quite a few stations (particularly in continental Europe) who inhabit the no man's land just off the end of the MW band between 1611 and 1640 kHz.
Of course I couldn't possibly condone any activity which would lead you to listen to a pirate and thus break the law in doing so. But at least now you might be able to stop yourself from committing this heinous crime before you get caught!
Friday 3 March, 2006, 11:49 - Much Ado About NothingBroadband wireless ADSL modem/routers are now available for below GBP50, incorporating, as the name suggests, a WiFi router, ADSL (and now ADSL2/2+) modem and often an Ethernet LAN connection. At this price, there's really no excuse for sticking to wired broadband access unless your house is so large that a single wireless access point won't cover all the various wings and annexes.
But things have gone even further than that so that some of the aforementioned modem/routers now include VoIP (Voice over Internet Protocol) connections. With a VoIP connection you can connect a regular phone to your modem/router and send and receive phonecalls via the internet through services such as Sipgate.
I recently came across a 'Wireless ADSL VoIP modem/router' for just over GBP90 including postage and the dreaded VAT so I decided to go for it. The sexily named 'Billion 7402VGL BiPAC' (available from broadbandbuyer.co.uk) provides:
* An ADSL2/2+ modem (backwards compatible with good ole' ADSL)
* A WiFi 802.11g access point (backwards compatible with good ole' 802.11b - both operate at 2.4 GHz)
* 3 100 Mbps Ethernet LAN connections (backwards compatible with good ole' 10 Mbps Ethernet)
* 2 VoIP phone sockets (the 'Billion 7402VGP BiPAC' is even backwards compatible with good ole' PSTN as well)
After a bit of a kerfuffle setting it up, I now have a wireless broadband network (so I can use my laptop in the bath); my main PC connected via the LAN; and a phone with a central London phone number sat on my desk that rings like any other phone but for which I pay no additional line-rental (other than that I already pay for the line which brings the ADSL connection into the house). Being a central London number I can now pretend to my work colleagues that my office is in a swish, high rent district of the city, rather than the sleepy backwater where it acually is! Oh, and it's possible to call other VoIP users for free, so I can chat to my friend in Dublin for nothing whatsoever.
The whole thing is rather impressive (I guess I am easily impressed) and there's still a spare phone socket on the back of the unit so I could get another phone number in, for example, Australia. Why? I don't really know, it's just a gratuitous and pointless use of technology. Plus, I always fancied living in Sydney!
Thursday 2 March, 2006, 09:48 - Spectrum ManagementSpectrum administrations or radio regulators, whatever phrase you care to pick, tend to be staffed by enthusiastic and intelligent staff; after all, it's a complex field this radio malarkey. However, what most staff lack (and most would readily admit to) is any real experience or expertise in the radio spectrum itself. Why is this? Well, other than working for a regulator or a radio user (such as a mobile or broadcasting company) there are very few ways to gain any real radio skills. For example, most degrees in technology of one kind or another will cover 'telecommunications' and may even stray into 'electromagnetism' but few, if any, give any real chance to learn about the radio spectrum, how it is used and how to manage it. There are various manufacturers who offer training on their suite of spectrum management software and monitoring hardware, which is great if you happen to have their tools, otherwise it would be like learning how to ride a bike and then being given the job as a traffic cop!
Posted by Administrator
Posted by Administrator
Step up to the lectern then, various organisations who have put together training courses which can be taken by anyone but are aimed at giving the opportunity to learn about this fascinating subject. That being said, there are not many such organisations: in fact it would seem there are only a small handful in the world!
The first such organisation is the National Telecommunications and Information Administration (NTIA). The NTIA runs an annual Spectrum Management Training Seminar over a one week period, however this is only open to 'U.S. Government agencies and contractor personnel nominated by Federal agencies'. With only 25 spaces, the course is always over-subscribed so the chance of getting a place is small. Not a great start! However, the NTIA, together with the United States Telecommuications Training Institute (USTTI) run another annual radio frequency spectrum management course every spring which is open to 'representatives of developing nations', who are sponsored by the U.S. government and thus can attend the course for free!
The USTTI (which is a joint U.S. Government and industry sponsored, not-for-profit organisation) also run a number of courses of varying lengths covering spectrum management and spectrum monitoring, each of which is sponsored by a manufacturer (such as Agilent, TCI or Rohde & Schwarz). The USTTI courses are provided for free, whilst participants have to cover their travel and subsistence costs, and applications have to be made 16 weeks (4 months) in advance. Nothing in life is every truly free and given the level of sponsorship which the commercial organisations must give to each event, one wonders how much of a sales pitch such courses are.
Next are the Telecommunications Regulatory Master Classes (TRMC) run by a UK company called InterConnect Communications (ICC). The TRMC's last a week and provides a solid grounding in all aspects of spectrum management. The course is not cheap at over GBP2750 for a week but this does include accomodation and most meals. The course programme appears to be aimed specifically at giving plenty of relevant information to attendees whether experienced or novice and the presenters are all experienced and knowledgeable. Best of all, the course is independent of suppliers or vendors which means that the one thing it isn't is a sales pitch!
Finally, there is a course entitled Understanding Modern Spectrum Management which is run jointly by spectrum publisher PolicyTracker and transport and telecommunications technology consultant Helios. This course is split into two parts: an initial 'technical' section designed to allow attendees to understand what spectrum is and how it fits together (and why, for example, some frequencies might be worth more than others); and a second, high level policy discussion on some of the 'hot topics' in spectrum. Again it is independent of suppliers or vendors. The cost is similar to the TRMC at around GBP2750 for 5 days, and it is held in the prestigious Oxford University.
There must be other courses elsewhere in the world: If you know of any please contact me as I'm forever getting asked what is out there.