Towards the beginning of November this year, Ofcom conducted a massive series of raids on pirate radio stations in London, and event considered news-worthy even by the BBC.

The operation closed 53 pirate FM stations in London and whilst some of the bigger stations are now back on-air, for some stations, losing a transmitter may mark the end of their broadcasts for some time. One station (On Top FM) also had a studio raid which can be devastating, and is certainly much more difficult to recover from.

What is interesting about this surge of activity by Ofcom is not that it was long overdue, or that it was so widespread, but was some of the 'anti-pirate' propaganda that Ofcom, a supposedly respectable body, spouted in their press release.

"Illegal broadcasting causes interference to the radios used by critical safety of life services such as the London Fire Brigade and National Air Traffic Services (NATS)."

Let's examine this statement. The London Fire Brigade uses frequencies of 70.5 - 71.5 MHz paired with 80.0 - 82.5 MHz, 148.825 MHz (for pagers), various frequencies between 450 and 453 MHz paired with 464.9 - 467.9 and 457 - 457.5 paired with 462.5 - 463 MHz. Now unless I am mistaken, none of these frequencies are directly affected by transmissions in the FM band (87.5 - 108 MHz) otherwise they would receive interference every day from the legal stations. Indeed other than for the fourth harmonics of transmitters on 90-90.6, 93-93.5 (actually BBC Radio 4 in London), 91.4-91.5 and 92.5-92.6 MHz, it's difficult to see where their problem arises. So if the Fire Service are suffering interference from pirate transmissions it is probably from one of two sources:

(1) The FM transmitters used by the pirates are of such low quality that they emit spurious signals on lots of frequencies. This is certainly possible, especially given the low-cost nature of the transmitters that pirates use, however the chances are that any transmitters prone to spurious emissions will be tracked down immediately as they will be causing interference to potentially hundreds of users.

(2) It is not the FM transmitters that cause the problem but is, instead, the link transmitters which are used to connect the pirates' studios to the transmitter site. Such links normally operate either in Band I (47 - 68 MHz) or at microwave frequencies. Microwave links are hardly likely to cause interference but it is feasible that the Band I links might if their frequencies co-incided with those used by the Fire Service. However, I doubt that any pirate would use a frequency knowing that it might interfere with the emergency services, even though they are operating illegally, they are not stupid enough to intentionally cause interference and risk the wrath of Ofcom.

There is one other possibility. The frequencies used by the Fire Service in the UK are used in some Eastern European countries for FM broadcasting! The 'OIRT' band covers 66 - 74 MHz and high-power transmitters still provide service in countries such as Russia, Moldova and Hungary. During certain propagation conditions, such stations are often heard in the UK (they do use high powers after all) and whilst I suspect that most firemen would know the difference between Russian and English, if they just hear music over their radio system they are going to assume it's a pirate.

So do the pirates cause interference to the Fire Service or not? Well I have no reason to doubt John Anthony, London Fire Brigade Assistant Commissioner who claims that, "... radio transmissions interfere with, and sometimes entirely disable, the communications systems the London Fire Brigade relies on." But is it really pirates or could it be the Russians instead?

Next onto the Air Traffic Service. They use many frequencies but in particular use 108 - 137 MHz which is directly adjacent to the FM band. A report from 1997, 'Investigation of Interference Sources and Mechanisms...' showed that illegal transmitters were a constant source of interference to both navigation and communication. This is easier to understand as spurious emissions from a transmitter are usually close in frequency to the main transmission thus spurii in the band 108 - 137 MHz are not unlikely. Thus I don't necessarily doubt 'A spokesman for NATS' who said, "Unauthorised broadcasts on or close to frequencies used by air traffic controllers can interfere with the passing of vital information between air traffic controllers and pilots. They can also affect the navigation aids used as landmarks." Point to Ofcom!

"Illegal broadcasting also causes interference to legitimate radio stations, denying hundreds of thousands of listeners the opportunity to hear their favourite programmes."

Does it now? Well in some cases yes. Drive past a pirate transmitter and if you are tuned to a nearby frequency there is every likelihood that you will hear the pirate 'splattering' over the top of the station you were trying to listen to (though the same thing would also happen if you drove past a legal transmitter). However, some pirates operate 200 kHz or less away from legal stations which is insufficient to prevent such interference (legal stations typically leave a gap of 400 kHz to prevent these problems occuring). However legal stations typically use much more power than pirate stations and the effect is very localised (and anyway whose to say that your favourite programme isn't on a pirate station...)

It is only in desperation, however, that pirates would choose a frequency likely to interfere with a legal station. In London such desparation stems from the lack of available frequencies (as most are already used by legal and other pirate stations). Given the option, most pirates choose a frequency as unlikely as possible to interfere with legal stations as it's much more likely that a complaint will be received against them if they do cause interference as if they don't.

Overall I suspect that pirate radio does cause interference in one or two cases, however in many cases it operates quite happily without causing problems to anyone else. Kudos to Ofcom for having a go at the problem, but only time will tell whether they will make any dent on the runaway train of stations that inhabit every nook and cranny of the FM band in London (and in some other major cities).

Of course there are other solutions, one being to actually licence the stations concerned and bring them into a controlled environment. Ofcom has already licensed about 30 community radio stations, however it claims that such services can only be licensed in remote areas where spare frequencies exist. A change in planning rules to recognise the low potential for interference that properly organised low-power FM stations cause might open up the band to more users and solve the pirate problem in a much more effective way.