Friday 29 October, 2010, 16:06 - Radio RandomnessEver wondered what goes on in those increadibly high frequencies that might almost be called 'nanowave' instead of 'microwave'? Well other than a bit of use for looking at the earth from satellites (a.k.a. earth observation) the main uses tend to be military. This is partly because it becomes quite difficult (and thus expensive) to generate any kind of power at these frequencies but also because even if you do, it doesn't tend to go very far because of the poor propagation characteristics. At these frequencies, signals do not penetrate very far inside solid objects such that even the thinnest membrane will stop them dead in their tracks. Even the thin blue line of atmosphere that surrounds our fragile planet is enough to nobble extra high frequencies.
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But those clever military people realised that this ability of signals to not penetrate anything very deeply might have an application other than for radio communication, navigation or any of the other uses you normally associate with the spectrum. They realised that a microwave oven at a frequency of, say, 95 GHz, would only cook the very outside of anything that was put in it (at a depth of no more than a half a milimetre) and leave the insides untouched. So you could use it to char the skin of a red pepper (or capsicum as they are known in lesser countries) whilst leaving the flesh crispy and fresh. Or you could char a peach, leaving the juicy bit inside uncooked. Or you could fire a beam at a human and make them feel as if they were on fire without actually burning them. No, seriously, not only could you do this, but this is exactly what a new line of devices being used by the military (and some other governmental bodies) are actually doing.
Known as the 'Active Denial System' (or ADS for short), these devices were initially designed to use for dispersing unwanted crowds gathering at military establishments, enclaves, camps or hide-outs. By blasting protestors, marauders and other such types with several hundred watts of high frequency 95 GHz microwaves in a tightly focussed beam, you can make them feel as if they are on-fire by heating up the nerve endings near the surface of the skin without heating the skin itself. This makes for a pretty good deterent and they soon move away, out of the beam.
Prisons soon realised the potential of the ADS to 'gently direct' prisoners away from certain areas too. Los Angeles County prison has installed one of these devices and according to the prison chief officer, "we likes 'em California char grilled", though it is unclear whether he was referring to his prisoners or to his burgers.
Sadly, attempts to use the device to produce instant suntans failed, partly due to the excrutiating pain involved in standing in front of the beam but also because it's completely the wrong type of radiation! Silliness aside, if such a device could be reduced in size to become handheld, it might be possible to generate enough oomph to produce a 'heat ray' beam to temporarily disable miscreants in your immediate vicinity. Now we have moved from HG Wells' martian heat rays to Gene Roddenberry's phaser guns. What with Star Trek communication devices having been introduced in the 1990s, and Star Trek style tri-corder being oh-so similar to iPhones, the time is nigh for someone to develop a real-life warp engine to propel humanity into the future. By the way, whilst you're there, could you check whether our Oidar is working and send us a message backwards through time to let us know. Ta muchly.
Wednesday 29 September, 2010, 14:36 - Radio RandomnessWhen is a radio not a radio? When it's a cake? Well obviously, but it wouldn't be a Wireless Waffle article if it was about cake now would it? Waffles perhaps, but cake?
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Anyhow the correct answer is 'When it's a Feynman Radio'. What, I hear you ask, is a Feynman Radio. In order to answer that we have to step back in time to the works of the Maestro James Clerk Maxwell. His Electromagnetic Wave Equation is the mathematical basis of all radio signals, propagation and so forth and desribes how radio waves travel.
Maxwell's equations (in common with many) square numbers before operating on them. One of the key numbers which is in Maxwell's equation is 't' standing for 'time'. The equations describe how Electromagnetic (radio) waves change with time. However, the factor which accounts for time is squared. Now this in itself may not seem important BUT the square of a negative number is the same as the square of a positive one. So, according to Maxwell's equations, a radio wave will look identical whether it has travelled 5 seconds forwards in time or 5 seconds backwards in time! Whoa! Hang on there a minute (or minus a minute). Does this mean that every radio transmitter emits two waves, one which travels forward in time and one which travels backwards? Well that's where Richard Feynman comes in. He argues that not only is this true, but that it is true of all atomic and sub-atomic particles and that for every occurance where something travels forward in time, the same thing happens and travels backwards.
But this is rubbish right? If it were true, we would be bombarded by endless radio signals and light beams from the future. This, argue many people, is evidence that the whole idea of signals travelling backwards in time is just a mathematical theory and not a practical reality. Others argue that the whole notion of 'deja vu' is a perfect illustration of why there must be a way of seeing into the future.
But maybe the fact that we can't hear 'backwards' radio signals is down to something much more straightforward. For example:
* Radio signals travel at the speed of light. Those coming backwards from the future would cross our own path going backwards at the speed of light. We, on the other hand are travelling fowards at the speed of light. Our paths, therefore, cross at twice the speed of light which means the backwards signals would be, to all intents and purposes, invisible.
* Radio signals travelling backwards from the future would be on negative frequencies. As all existing radio receivers only tune to positive frequncies, ie those above 0 MHz, we are unable to receive them. A receiver tuned to minus 900 kHz would presumably receive future radio broadcasts perfectly well.
Here at Wireless Waffle headquarters, significant effort is being put into the development of a negative frequency radio, or an 'oidar' as we like to call it. Using things such as negative impedance converters we are seeking to synthesise a capacitor of several hundred negative picoFarads and an inductor of the appropriate number of negative microHenries such that they resonate at a negative frequency. Using a 'edoid' we hope to rectify any signals recived to feed a set of headphones. A negative antenna (an 'annetna') is proving more difficult, however we believe that a modified slot antenna in which the radiating element is a hole in a plate of metal rather than a traditional antenna which is metal in the middle of a hole (eg free space) may just do the job. Burying the annetna underground may also help but until the whole receiver is functioning it will be difficult to check.
Occasionally Wireless Waffle has been known to produce a few spoof entries (especially around April 1st!) however the Feynman Radio is real (try checking on the web). Our attempts to develop an oidar however may just be a reverse-time echo of something we failed to achieve several years from now.
Wednesday 25 August, 2010, 04:10 - Pirate/ClandestineBack in October 2009, Wireless Waffle brought to your attention the HF (short-wave) monitoring data produced on a quarterly basis by the ITU. Within these reports were a number of short-wave pirate stations and the original list of stations brought a lot of interest from these stations, both to see who had been 'caught' and to see how close the ITU had gotten to identifying their exact location. Based on the e-mails that were received following the article, it seems like some had hit the nail a little too closely on the head for comfort.
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To see how the ITU were getting along, and who had been spotted more recently, a trawl of the montoring reports from January to June 2010 has been conducted and the results presented below. Those stations whose name is shown in CAPITALS were directly identified by the monitoring station concerned. Those in lower case have been identified using the various on-line blogs that report pirate reception.
|Date||Time (UTC)||Freq (kHz)||Monitoring Station||Location||Station|
|03 Feb 10||0600-0600||4025||Berlin, Germany||UK||Laser Hot Hits|
|23 Feb 10||0000-0630||4025||Tarnok, Hungary||Laser Hot Hits|
|23 Feb 10||1830-2359||4025||Tarnok, Hungary||Laser Hot Hits|
|21 Apr 10||1830-2400||4025||Berlin, Germany||Laser Hot Hits|
|02 May 10||0600-2359||4025||Rambouillet, France||0W10 52N01 (Baldock, UK!)||Laser Hot Hits|
|23 May 10||0000-0630||4015||Tarnok, Hungary||Laser Hot Hits|
|16 May 10||1900-2212||5814.7||Rambouillet, France||0E17 52N45 (King's Lynn, UK)||Radio Telstar South|
|16 May 10||0700-0915||5815||Rambouillet, France||6E11 52N30 (Zwolle, Netherlands)||Orion Radio|
|27 Jun 10||0630-0820||5820||Tarnok, Hungary||Orion Radio|
|11 Apr 10||0854-0908||6203||Vienna, Austria||Radio Scotland International|
|09 Feb 10||1048||6210.2||CCRM, Belgium||Netherlands||MISTI RADIO|
|10 Jan 10||1818-2246||6220||El Casar, Spain||11E24 44N27 (Bologna, Italy)||Mystery Radio|
|20 Jan 10||1812-2350||6220||El Casar, Spain||11E24 44N27 (Bologna, Italy)||Mystery Radio|
|30 Jan 10||2002||6220||Baldock, UK||10E0 43N50 (Pisa, Italy)||MYSTERY RADIO|
|28 Feb 10||1100-1137||6220||Vienna, Austria||11E0 44N0 (Prato, Italy)||RADIO MARABU|
|06 Mar 10||1800-2350||6220||El Casar, Spain||11E24 44N27 (Bologna, Italy)||Mystery Radio|
|21 Mar 10||2012-2355||6220||El Casar, Spain||11E24 44N27 (Bologna, Italy)||Mystery Radio|
|06 Apr 10||1852-1917||6220||Vienna, Austria||Italy||MYSTERY RADIO|
|10 Apr 10||1900-2359||6220||El Casar, Spain||11E24 44N27 (Bologna, Italy)||MYSTERY RADIO|
|13 Jun 10||1730-1800||6220||Klagenfurt, Austria||12E0 43N0 (Perugia, Italy)||Mystery Radio|
|14 Jun 10||1700-1900||6220||Rambouillet, France||10E43 43N45 (Prato, Italy)||MISTERY RADIO|
|15 Jun 10||0700-0800||6255||Rambouillet, France||Netherlands||Cool AM|
|19 Jun 10||1530-1645||6374.1||Rambouillet, France||4E13 51N59 (Den Haag, Netherlands)||Radio Baken 16|
|09 Feb 10||0944||6299.2||CCRM, Belgium||RADIO RAINBOW|
|30 Apr 10||1918-2005||6375||Vienna, Austria||Netherlands||Radio Relmus|
|09 Feb 10||0914||6376.6||CCRM, Belgium||Netherlands||RADIO DUTCH WING|
|20 Jun 10||1015-1600||6399.9||Rambouillet, France||1W45 51N21 (Marlborough, UK)||Laser 558 relay|
|11 Mar 10||1815-2200||6870||El Casar, Spain||9E7 45N18 (Milan, Italy)||RADIO PLAYBACK INT|
|11 Apr 10||1500-1700||6959.9||Rambouillet, France||4E39 51N41 (Breda, Netherlands)||Radio Jan Van Gent|
|03 Jan 10||0800||7610||El Casar, Spain||Italy||RADIO AMICA|
|10 Apr 10||0600-2115||7610||Rambouillet, France||12E56 43N55 (Pesaro, Italy)||RADIO AMICA|
|11 Apr 10||0530-0600||7610||Rambouillet, France||12E56 43N55 (Pesaro, Italy)||RADIO AMICA|
|10 Apr 10||1247-1407||7610||Vienna, Austria||11E30 44N30 (Bologna, Italy)||RADIO AMICA|
Please be assured that it is not our intention to name and shame these stations in any way, nor is the Wireless Waffle team opposed to hobby broadcasting (for want of a better word) but we do believe that the stations concerned should be aware that their location may not be as secret as they had hoped.
The question of how accurate these measurements are is a good one. The level of concern that seemed to arise from the previous list suggests that they may be relatively good. However, let's take a real example. There are 10 measurements relating to Mystery Radio. Of these, five different locations are logged. The map below shows the position of these loggings.
The distance between the closest of all these measurements is around 20 miles (32 km). It is possible that this is the best resolution that some of the monitoring stations can achieve. At this kind of resolution, a ground-based receiver would be unlikely to hear the transmitter. Ground wave signals would not travel this far, and it is the ground wave signal which is required for a person on the ground to be able to 'home in' on the location of a transmitter.
So should pirate radio stations be concerned about being tracked down as a result of the work of the ITU. From the evidence above, it seems that this data alone is probably insufficient to allow a station's location to be identified in one simple move. However, if you are running one of these stations and the location which is shown is more accurate than those for Mystery Radio - and certainly if its within 5 km at which point a man on the ground would be able to track you down - perhaps it's time to up sticks and find a new site!
Tuesday 10 August, 2010, 05:17 - BroadcastingOne of the most common questions that the Wireless Waffle team are asked by those setting up radio transmitters is, "How much power do I need to cover an area X miles wide?". Such a question is virtually unanswerable as there are so many factors to take account of including the frequency of operation, the topography of the area, the kind of structures (buildings, trees) which are in the required coverage area, what kind of receivers people are using and much more. The observant will note that these factors are not ones which can necessarily be changed by the person operating the transmitter - unless they fancied chopping down a forest for example. What can be changed at the transmitting site are two relatively simple factors: the height of the antenna, and the power of the transmitter.
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Such discussions therefore end up focussing on how high the antenna needs to be and what power the transmitter should be. But which is most effective in increasing coverage: height or power?
Let's tackle height first. Assuming we are trying to provide a signal over the earth and that there are no obstacles at all and that the earth has no undulations (hills and so on), then the range of a transmitter can easily be calculated from a simple line-of-sight rule. This tells us that for a particular height above the ground, the horizon (and thus the edge of the coverage area) will be a specific distance away. One oddity in this is that radio signals tend to get defracted a little by the Earth's atmosphere which has the effect of making the planet appear slightly less curved and thus extends the radio horizon about a third beyond the optical horizon. The chart below shows the optical and radio horizons for a transmitting antenna mounted at a certain height.
With an antenna about 10 metres above the ground, the radio horizon is about 10km away. If the height of the antenna is increased to 50 metres, the radio horizon increases to about 24 km - a very healthy improvement. It's perhaps worth noting that 'height above ground' could be generated by raising the height of the antenna, or by mounting it on top of heigh point (eg a hill).
Increasing the transmitter power also increases coverage, but not in quite the same way. Getting signals much beyond the radio horizon relies on various odd propagation techniques including refraction, defraction and scatter. In free space, increasing the power by a factor of 2 will increase the distance at which the signal is of equal strength by the square root of 2. So, if the signal is 30 dB at a distance of 10km, increasing the power by a factor of 2 will move the point at which the signal is 30 dB to a point approximately 14km away from the transmitter. Sadly, the Earth is not generally a 'free space' environment and signals fall away much quicker than this, even before the horizon is reached. The chart below shows a simulation of coverage for different transmitter powers, assuming an antenna height of 20 metres.
The distance to the radio horizon for a 20 metre heigh aerial is 15 km and in 'free space', in this example, this is reached by a power of 10 Watts. For the 'real life' example, 10 Watts only achieves a distance of around 10 km because of the fact that the Earth is not a free space environment. To achieve 15 km in 'real life' requires a power of nearer 50 Watts. What is immediately clear is that enormous increases in power are required to extend coverage. Even with 100 Watts, in our theoretical example, the distance acheived is still less than 20 km.
Increasing the height of the transmitting antenna is therefore, theoretically, a much more effective way of increasing coverage than turning up the power. Of course, it's not always possible to put up a high antenna, and in this situation more power is clearly better, but in general height wins every time. To show the difference, the map below (made using Radiomobile) shows the coverage for a transmitter nominally located in the centre of Oxford. It's animated (oo-err!) and cycles through the coverage which would be acheived for:
* A 10 Watt transmitter with an antenna height of 10 metres
* A 40 Watt transmitter with an antenna height of 10 metres
* A 10 Watt transmitter with an antenna height of 20 metres
The coverage achieved in the latter two cases is very similar, however in the map with the higher antenna, the coverage is more 'solid' than that with higher power. If this were a radio station, the higher antenna would provide a more reliable signal, especially for people on the move, than the lower antenna with higher power. The extent of the advantage of height over power means that it is generally more beneficial to identify an elevated transmitter site towards the edge of an area where coverage is required, rather than settle for one which is nearer the centre but lower. A transmitter on a hill overlooking a town will provide more solid coverage in the town for the same transmitter power than a site in a town centre. Hopefully, those now considering how best to maximise their coverage will think beyond Watts and consider that factor well understood by estate agents, location, location, location.