Wireless Waffle - A whole spectrum of radio related rubbish

Roof Raiders II - The Council of Lifesignal strength
Wednesday 27 February, 2008, 09:49 - Pirate/Clandestine
Posted by Administrator
lara croft roof raiderIt seems as if Ofcom has been up to its tricks again. On February 19th they announced that they had conducted another large-scale raid on London's pirate radio stations similar to one it conducted in 2005, however this time it was in conjunction with the local council authorities whose buildings are often the home of the pirates' transmitters. 22 transmitters were seized and 3 people were arrested.

I won't repeat the musings I made last time this happened concerning the probability of pirates causing the kind of wide-spread radio interference they are accused of. The latest news release from Ofcom actually plays down the interference aspects compared to their previous press release, and now plays up the difficulties and dangers that councils face due to the damage caused to property when pirates break into buildings to install their equipment. There can be no doubt that such damage does get caused when pirates break into lift-shafts and onto the rooves of blocks of flats which, if anything, only serves to highlight the desperation that such stations face and their determination to bring the kind of music they play to their audiences. Clearly mainstream radio is not catering for a whole swathe of society.

spondwick by ormWhether or not they are working in cahoots or not, it seems that the BBC is intent on reducing the number of frequencies which might otherwise be useful to community (or pirate!) radio broadcasting. It has recently expanded coverage of 'Three Counties Radio (3CR) by adding relay stations in East Herts, South Herts and High Wycombe. However unlike the majority of other BBC local radio stations, these relays use frequencies in the bands usually used by the BBC for relays of national radio stations (90.4, 92.1 and 98.0 MHz respectively). Now the BBC are quite at liberty to use their own spectrum as they see fit, but this move away from a logically planned system to something more flexible surely suggests that a similarly flexible approach might be taken on a wider basis to allow for frequencies for more, new, innovative radio stations rather than just repeating existing ones. These three frequencies could have been used for new commercial or community stations in these areas. It's not that BBC coverage did not exist there before, it's just that it wasn't quite as good as the BBC had hoped.

I still maintain that it's quite possible that pirate stations can (and do) cause interference to legitimate users of the radio spectrum. It's clear, though, that Ofcom is only making small inroads into solving the problem and that other parties are doing nothing to assist. There has to be a long-term solution to the problem if it is ever to be solved and one commentator has suggested that when radio broadcasters have moved over to digital broadcasting (whether DAB, DRM, or something else), some of the 'digital dividend' that results should be given to low power, lightly licensed, radio broadcasting. Sounds like an eminently good idea to me.
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Stereo-Phonicssignal strength
Friday 8 February, 2008, 19:10 - Licensed
Posted by Administrator
radio bognor logoThe Wireless Waffle team used to supply VHF FM radio transmitters for Restricted Service Licence (RSL) stations in the UK. The licences allowed a maximum transmitter power of 25 Watts and a maximum antenna height of 10 metres above the ground. As such, the range of such stations was normally very limited compared to regular FM stations who used powers typically in excess of 400 Watts and with much higher antennas. To maximise the range of the RSLs, it was best to identify and use transmitter sites which were as high above the surrounding land as possible but in some areas the land was so flat that no such sites existed.

One question which was constantly asked by the operators of such stations was, "Should I broadcast in stereo?". On the face of it, stereo is the norm for FM broadcasts and most stations believed that if they weren't in stereo they would be seen somehow as inferior. However, what most failed to take into account was the fact that in order to receive a good quality stereo signal, the signal strength has to be 10 times (20dB) higher than that required to receive a good quality mono signal. This translates into a reduction in coverage area of 100 times, i.e. the coverage in stereo is only a hundredth of the coverage area achieved by the same transmitter in mono (ignoring topographical issues such as terrain and buildings).

Why is there so much difference? The answer lies in the bandwidth which a stereo signal occupies compared to a mono signal. The audio bandwidth of an FM transmission lies in the range of 30 Hz to 15000 Hz (15 kHz). However the way that a stereo signal is generated expands this bandwidth to 53000 Hz (53 kHz). (Don't get this confused with the RF bandwidth of the signal which is 180 kHz for mono and 256 kHz for stereo).

fmspectrumHow does the audio bandwidth extend to 53 kHz? Well the mono signal which is made by adding the left (L) and right (R) channels together - expressed as L+R - is transmitted as usual so that the resulting signal is compatible with mono receivers. The difference between the left and right channel (L-R) is amplitude modulated onto a carrier at 38000 Hz (38kHz). This produces a signal which occupies the audio frequencies from 23 to 53 kHz - above the standard audio range and thus inaudible on a mono receiver.

A 'pilot' tone which is a low-level tone at 19000 Hz (19kHz) is also added to this signal and then the whole lot is sent to the FM transmitter. In a stereo receiver the presence of the pilot tone triggers the stereo decoder to recover the original signals. The left channel is reproduced by adding the mono to the stereo difference signal (L+R+L-R=2L) and the right channel is produced by subtracting the difference signal from the mono signal (L+R-(L-R)=L+R-L+R=2R).

The noise received by an FM receiver increases as the square of the bandwidth of the modulated/demodulated signal and as such the increase in noise (i.e. the decrease in signal to noise) for a stereo signal is (53/15)² or 12.5 times. Some of this increase is counterbalanced by 'pre-emphasis' where higher audio frequencies are enhanced before transmission and then reduced at the receiver, reducing the effect of some of the noise. The resulting improvement leaves a difference of the factor of 10 mentioned above.

hisssThe question of whether to broadcast in stereo for a low-power RSL (or indeed a pirate!) FM station is therefore a question of quality and coverage. If you have a high site and can expect that most of the listeners you wish to target will receive a good strong signal, stereo is great. If not (which is usually the case), using mono ensures your coverage is maximised. Of course, in fringe stereo areas where the signal becomes 'hissy' the listeners could always switch to mono, but how many people actually know that this solves the problem, let alone know where the mono/stereo switch on their receiver is?!

There are some pirate stations who transmit only the pilot tone so that the stereo 'light' on receivers comes on, which looks nice, but don't actually transmit in stereo. This is the worst possible case, as all it will serve to do is reduce the coverage, without giving any additional benefit to the listeners!
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How to listen to UFOssignal strength
Friday 31 August, 2007, 10:48 - Pirate/Clandestine
Posted by Administrator
Since the late 1990's rumours have abounded that it was possible to hack into American military satellites and use them for wide area communication. The satellites, originally the 'FleetSatCom' newtork (often abbreviated to FLTSATCOM) use basic FM modulation and have uplinks in the area of 300 MHz and downlinks in the area of 260 MHz. Stories went that tuning in to the downlinks it was possible to hear illegal pirates, from Brazil in particular, who were usurping these US military satellites to use for wide-area communications. It was also said that 'Smile 93.9 FM' (rumoured to be from Manila) was using one of the channels as a studio to transmitter link and could often be heard on the downlink frequency of 269.950 MHz.

This seemed a little far fetched and unbelievable: How could one of the world's most super-sophisticated armed forces allow their multi-million dollar military hardware be taken control of by such an unsophisticated enemy armed with nothing more than a simple UHF FM transmitter? Using a simple VHF/UHF receiver and a bog standard roof mounted VHF/UHF antenna, I set out to try and debunk the myth.

Within seconds I was listening to a conversation between two likely sounding chaps on a frequency of 255.550 MHz. Next I stumbled across more voice traffic (definitely in Portuguese, the language spoken in Brazil) on 258.650 MHz. And before long I found more voice traffic on 253.850 MHz. Intrigued that this long reported phenomena was still in evidence I did a bit of digging on the internet to find out more.

The original FleetSatCom satellites which were launched in the late 1970's and early 1980's are no longer operational. They were initially replaced by satellites known as Leased Satellites (Leasat) which have also since been replaced by the UHF Follow-On series of satellites, ironically acronymised as UFO. The UFO satellites continue to provide the same communications capabilities as the earlier ones but with somewhat higher transmitter powers, making reception of them fairly straightforward.

A bit more digging uncovered military standard MIL-STD-188-181A which describes the interface specification for the satellites (i.e. the technical requirements for equipment used to access them) and in it we find a list of the uplink and downlink frequencies used. All the frequencies I could hear are in group 'Charlie', now known as group 'Quebec' (Q) on the UFO satellites. Group Q comprises the following 25 kHz wide downlink frequencies (uplink frequencies are 41 MHz higher):

ufo fltsatcomQ1 250.650 MHz (Fleet Broadcast)
Q2 252.150 MHz (Navy Channels)
Q3 253.850 MHz
Q4 255.550 MHz
Q5 257.150 MHz
Q6 258.650 MHz
Q7 265.550 MHz
Q8 267.050 MHz
Q9 269.450 MHz
Q10 269.950 MHz
Q11 260.625 MHz (DoD Channels)
Q12 260.725 MHz
Q13 262.125 MHz
Q14 262.225 MHz
Q15 262.325 MHz
Q16 262.425 MHz
Q17 263.825 MHz
Q18 263.925 MHz

So far, I have heard sporadic voice traffic on channels Q2, Q3, Q4, Q5 and Q6 and something, albeit rather weak on Q7. It seems as if the satellite I am hearing is UFO-7 which is situated over the Atlantic. But is this traffic really pirates using the satellites on purpose, or is it something else? Surely there is no longer the need, in Brazil or other countries, to use US military satellites for communications, especially now that mobile phones and mobile coverage are virtually ubiquitous?

A quick look at the Brazilian frequency allocation table, the Plano de Destinação de Faixas de Freqüência, shows us that the frequency range 270 - 326.8 MHz is assigned to the fixed and mobile service, and in particular to public correspondence. So the frequencies are quite legally in use for various communication services; could it be that they are being relayed by the satellite is incidental and a result of the fact that the uplink frequencies are used differently in different parts of the world? So maybe there are no Brazilian pirate radio mafia trying to jam US military satellites after all then? What a shame, it seemed like such a good story.
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48 metre Bandanasignal strength
Wednesday 16 May, 2007, 14:14 - Pirate/Clandestine
anorakThere's a term used in the UK which takes its roots from an overgarment worn by many to keep dry on particularly squally days. The aforementioned garment is an 'Anorak', which is a kind of winter jacket which, no matter what you wear it with, will never look fashionable (the possible exception being Paddington Bear who at least looked cute, though it could be argued that Paddington wore a Duffle Coat rather than an Anorak if we're being pernickety). The Anorak is generally rather unpopular, being an ugly but practical kind of a coat; but due to the fact that it is a rather warm item to wear, those who spend a lot of time outdoors but do no exercise and thus are in need of something to stop them freezing whilst standing around have taken the Anorak to heart as their overcoat of choice.

But who, I hear you ask, would want to spend all day standing around doing nothing especially if it was cold or raining? A very good question! The Anorak became (and to some extent still is) the de facto uniform of those with hobbies such as train, bus or plane spotting, collecting number plates, "Oooh, V355LOX, a rare one from the OX series when they misprinted the 5 so that it looks like an S and it reads 'V35 SLOX'", watching grass grow, and so on... In the UK, however, the term 'Anorak' has come to be associated with anyone whose hobby is just a little bit weird, sits in a niche so small that only a handful of people understand it, is a touch excentric or is just very, very dull. And thus, most avid radio listeners, especially short wave listeners, DXers and even radio amateurs are regularly tarred with the Anorak moniker.

48mbtxWhy is this of much (if any) interest? Well the picture on the right (click it to see it in its full glory), which is a rather splendid example of a clandestine pirate radio transmitter, designed to transmit music programmes on short wave, brought me to thinking about why the stalwarts who built and operated such things continued to do so. I can think of 2000 or more salient reasons why it's no longer such a good idea:

1. No one (except Anoraks - see above) listens to short wave any more.
2. In most locations, the amount of background noise from computers, electrical equipment and the like makes short wave reception virtually impossible.
3. That aside, short wave reception does not lend itself to listening to music due to the annoying fading in and out.
4. If you want people to hear your radio presenting skills, there are easier and cheaper way of doing it - just upload a programme onto the internet.
5. There are 15,000 better things to do with your time (like collecting number plates for example).
6. If you get caught, the fines can be large (GBP2,000 plus 6 months in gaol).
7. And so on...

So why do the operators stations such as AlfaLima and WR International continue to spending their hard earnt cash and wasting their weekends building, setting up and operating such equipment. I would venture to suggest that there's still a real buzz associated with doing so. For a start, it's illegal, and flouting the law often gets the adrenalin flowing (not that I'd know of course). Then there's the kudos you get by being received by other short wave anoraks, 'Radio Flump was sounding hot last Sunday morning - SINPO 32232 - Best signal yet - I could almost make out what DJ Bobbisox was saying'. Also there's a little bit of exhibitionism and showing off in it, and that too provides an ego boost all of its own.

I argue, therefore, that the real anoraks are those people who tune into and listen to such short wave pirate broadcasts but make no attempt to join in the real fun and build a transmitter and get on air with the pioneers, pirates and thrillseekers who supply their fun to start with. So instead of tuning around the band, get your soldering iron out and build a Grenade or a Corsair, record a rubbish radio programme full of music that you think is cool but everyone else has forgotten, find a remote location, set up a transmitter early on a Sunday morning instead of lying in bed a couple of hours longer. And in the process... throw away your anorak and replace it with a skull and crossbones headscarf instead.
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