Wireless Waffle - A whole spectrum of radio related rubbish
SETI listening on the wrong frequency?signal strength
Friday 27 May, 2016, 03:40 - Radio Randomness, Spectrum Management
Posted by Administrator
Since the 1980s, extensive amounts of time and resources around the world have been focussed on the search for extra-terrestrial intelligence (SETI). One of the primary methods of doing so, is listening for radio transmissions from far away worlds. But how do you decide what frequencies to listen on?

alien lightning 2The main frequency that SETIologists believe would be the primary real-estate for aliens wishing to make themselves known is around what is termed the 'water-hole' at frequencies close to 1.5 GHz. This frequency range includes the so-called hydrogen line (1420.4 MHz) and hydroxyl line (1666 MHz) which are frequencies that are generated by naturally occuring processes within atoms. The other advantage is that Earth's atmosphere, which comprises quite a large percentage of water, is relatively transparent at these frequencies making Earth based observations easier. The logic is that any intelligent life would be as aware of these lines in the spectrum as we are, and would figure that these are good places to transmit. Whether the transparency of the atmosphere at these frequencies on the planets they inhabit would also point them in the direction of the water-hole is a moot point.

Other frequencies that have been considered are twice the water-hole frequencies (after all, intelligent life would surely be able to multiply by 2 - assuming their number system used the same integers as we do), or 4.462 GHz which is the hydrogen line times pi (because circles are a universal phenomena, right?)

But could we actually receive a transmission on such a frequency? Let's do the link budget calculation...
  • The path loss from our nearest star, Alpha Centauri, which is 4.37 light years (41,315,094,156,000 km) away at 1.5 GHz is 368 dB.
  • If we use a BIG dish, say 30 metres in diameter, to receive the signal, it would have a gain of 51 dBi.
  • Let's also assume that the aliens are transmitting using a similar sized dish (and they are pointing it directly at Earth).
  • If the signal is very low bandwidth data (say 100 bits per second) we would need a receiver bandwidth of around 100 Hz, giving a noise floor for a cryogenically cooled receiver of -168 dBm.
  • The necessary transmitter power to overcome the noise is therefore 368-51-51-168 or 98 dBm or 6.3 MegaWatts.
A 6.3 MegaWatt transmitter is not out of the question at these frequencies, so in theory, it might be possible. Of course planets orbiting more distant stars would need even bigger transmitters and the one slight flaw in this calculation is the need for the aliens to be pointing their dishes directly towards Earth. Take this out of the equation and you need a transmitter 51 dB bigger, meaning a transmitter power level of around 800 GigaWatts would be needed, even at Alpha Centauri, if an omni-directional transmit antenna was used.

But path loss is dependent on frequency, and so if a lower frequency was used, say 100 kHz instead of 1500 MHz, the path loss (from Alpha) drops from 368 dB to a more managable 284 dB (84 dB less). Unfortunately the gain of the receive dish also falls from 51 dB to a measly -33 dB (also 84 dB different). But instead of a dish, we could use a long-wire to receive the signals, at 1.5 km long, it would have a gain of 2 dBi, so overall we would gain 33 dB in our link budget calculation.

"A-ha", you say, "but the transmitting antenna would have a lower gain too, so nobody really wins. If I do the maths right, the required transmitter power is now 284+0+0-168 which is 116 dBm or 400 MegaWatts, which is a bit far fetched isn't it?" Maybe, but it's easier to generate 400 Megawatts at 100 kHz than it is at 1.5 GHz (or it is for humans anyway). In fact, this kind of power is generated every day on Earth by... lightning storms.

It may come as no surprise, therefore, that researchers at the University of St Andrews believe that signals that were received in 2009 from exoplanet HAT-P-11b might well have been caused by lightning storms on the distant planet. But what use is this, it doesn't represent extra-terrestrial intelligence, just extra-terrestrial weather (and we already know that even the other planets in our own solar system exhibit different weather characteristics).

alien lightning 1The point, if there is one, is that if we could modulate lightening storms, or perhaps induce them in a way that allowed them to occur in a predictable fashion, we could make signals big enough to be transmitted across inter-stellar space. According to Climate Viewer:
DARPA wants to trigger lightning to protect infrastructure, satellites, and use the artificially generated ELF waves to send messages worldwide. Lightning strikes are “triggered” at the University of Florida and University of Arizona, a network of sensors called the Holographic Array for Ionospheric Lightning (HAIL) collects info on these strikes, and HAARP has a large role in the whole process.

But if lightning can be heard many light years away, perhaps these artificially induced lightning strikes are nothing to do with their stated objective but are actually to 'send messages extra-terrestrially'. Maybe the signals received from HAT-P-11b are not just random lightning storms and despite the Daily Mail claiming that these are not messages from space, perhaps they are an attempt at communication after all. After all, stranger things have been true!

haarp antenna array
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Antipodean Gainsignal strength
Friday 1 April, 2016, 10:03 - Radio Randomness
Posted by Administrator
Despite it being a well-known phenomena amongst radio fanatics around the World, there is little written on the internet concerning a strange effect known as 'Antipodean Gain' and for that reason Wireless Waffle has decided to take it upon ourselves to enlighten anyone who is not familiar with it.

Antipodean Gain can impact any radio wave capable of traversing the globe and therefore mainly applies to short-wave radio signals but in theory could be valid for medium-wave and long-wave signals too if the radio propagation conditions are right. The idea is a relatively simple one: if two stations wishing to communicate are at antipodal points, which put in laymans' terms means that they are exactly on the opposite sides of the planet from each other, it does not matter which way you direct a radio signal from either point, it will be aiming directly at the opposing point.

santiago xian mapTake, for example, Santiago in Chile (70.7W 33.5S), and Xi'an in China (108.9E 34.3N). To within 100 km (60 miles), these two metropoles lie exactly opposite each other on the globe. Thus, no matter which direction you face when standing in Xi'an, Santiago ise around 20,000 km away and the same is true in the reverse direction. If you think about this from the perspective of radio signals: whilst signals normally spread out as they travel away from the transmitting antenna, with antipodeal metropoles the signals re-converge. Therefore any signal leaving the transmitter site will be directed to the receiving site and although they may have originally been spread out, the re-focussing of the signals will mean they add back together and the path between the two will have far less path loss than one which is of a similar length but is not antipodean.

The map to the right shows the World from the perspective of someone standing in Santiago. China is the circle which is in every direction you look, and the very edge of this is the city of Xi'an (the outer circle coloured in red), and so no matter in which direction you look, you will be looking towards Xi'an. The same would be true of someone standing in Xi'an: no matter which way they looked, they would be facing Santiago.

If this is still too complicated, just think of the North and South poles. It doesn't matter which way you face at the North pole, you will always be looking directly towards the South pole (and vice versa). And thus, an omni-directional antenna, which transmits in every direction, when used to communicate with a city on the opposite side of the Earth would effectively be a highly directional antenna, with all of its radiation focused on that city. Signals that would otherwise have spread out would be re-focused into a tight beam.

juan and xinIf this sounds all too unrealistic, work out which country is at the antipodal point of your current location and tune in to a short-wave radio station that is transmitted from that location. For the UK, this is pretty much New Zealand (although strictly speaking, New Zealand is antipodeal to Spain). For the USA and Canada, you are largely out of luck, as the opposite side of the planet mostly comprises the wide, open and empty expanses of the Pacific Ocean.

So now you know. And to help you calculate where your antipodeal point is, just enter your latitude and longitude (in decimal degrees) into the Wireless Waffle Antipodal Point Calculator below, and press 'antipodate me' and we'll do the maths for you. You can then click on the globe to the right and see the your location and that of your antipodal location on Google maps. As they say in France, 'Voila!', or as they say in China, 'Zhèli shì'!

Wireless Waffle Antipodal Point Calculator
Your Latitude (e.g. 33.9N)your location
Your Longitude (e.g. 108.9E)
Antipodal Latitudeantipodal location
Antipodal Longitude

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CBGB (Citizens Band Great Britain)signal strength
Friday 11 March, 2016, 13:34 - Radio Randomness
Posted by Administrator
dukesofhazzardWireless Waffle has been contacted by Will Hogan who is putting together a book entitled 'CBGB' which will celebrate the culture of CB radios across Great Britain in the 1980s. To let Will take over the commentary:
Inspired by the amazing artwork of Eyeball cards, we aim to interview enthusiasts to get a real insight from the people that made it happen, and explore the cards themselves.

We already have a bank of cards from Suffolk, and a few interviewees, but we really need more to show the national scope of CB culture at this time. I'll be working with award-winning photographer, David Titlow who specialises in portraits (his work can be seen at the National Gallery as he's the latest recipient of the Taylor Wessing portrait prize).

Absolutely any help we could get - even looking at Eyeball cards that anyone has - would be amazing. There's no pressure to talk or be quoted, but anyone who would be willing to would be fantastically helpful.

If you could help Will out, please get in touch with him. His telephone number is +44 (0) 7966 072826.
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Pirate radio to go digitalsignal strength
Saturday 23 January, 2016, 11:49 - Broadcasting, Licensed, Pirate/Clandestine, Radio Randomness, Spectrum Management
Posted by Administrator
The number of pirate radio stations on-air in London does not appear to have diminished over the past 10 or more years, despite there now being many legal ways in which stations could reach their audiences, most recently though streaming audio on-line.

brighton dab transmitterOfcom has recently proposed that many local radio stations could be accommodated on 'small scale DAB' transmitters which provide a localised service, and it is conducting a number of trials around the UK of such a service. The idea is to use low cost hardware and software to develop the DAB signals, for example using a USRP software radio, and the various software tools provided by the Open Digital Radio project. Using these, it is possible to put a (very) low power DAB station on-air for less than GBP1000 and with a suitable power amplifier (for example a 30 Watt Mitsubishi amplifier module, or how's about a 1.2 kW amplifier module), a DAB transmitter with reasonable coverage can be built for not that much more. Indeed research conducted for Ofcom suggests that a 100 Watt e.r.p. service using such technology could be provided to broadcasters for around GBP1400 per year (at a bit rate of 160 kbps which is far higher quality than most of the existing UK DAB services!)

An article in spectrum newsletter PolicyTracker entitled, 'Can DAB save us from the pirates?' (note - a subscription is required to read the full article), makes the point that the criteria which the UK has set to begin the digital switch-over of radio services (e.g. the turning off of analogue services in favour of digital) is almost upon us. The criteria is that 50% of UK listening should be on a digital platform (whether DAB, on-line, cable, satellite or other) and the latest figures show this is now up to 43%, though as Wireless Waffle has pointed out before, the proportion of digital listening appears to have stagnated. If the UK does set a date for the winding down of FM radio, one of two things could happen:
  1. pirates may move to digital platforms, in order to be found on the same dial as other stations; or
  2. pirates may take the opportunity of an emptier FM band to choose clearer frequencies, increase their power, or just increase the number of services.

The problem is that in either case there is no guarantee that the pirates would do this in a legal fashion. Pirate radio stations are not renowned for co-operating with each other so why would they pay to be on a DAB platform, rather than buy the equipment themselves and set up digital pirate stations? The answer might come in the form of the reduced number of frequencies available. In the FM band, assuming a station every 300 kHz (which is just about OK from an interference perspective), there is room for 68 stations on the dial. Taking into account the 20 or so legal stations already on-air in London (depending on what you count as London), this leaves a potential for 48 pirates. For DAB radio, which requires 1.4 MHz of spectrum to operate, there is room for just 32 transmissions in any one location. In London 4 of these frequency blocks are in use, leaving 28 'available'.

local dab radio"Ah", you say, "but each DAB multiplex can carry 10 or more stations, so really the number is 280". That is true, but this requires the pirates to club together to buy and operate the equipment and, as already stated, they aren't that good at this. Perhaps the business model they employ could change, and a smaller number of illegal transmitter operators could provide services to multiple pirate stations. Or perhaps a small number of legal transmitter operators could provide the same service. The problem here seems to be that in order to legitimise the pirates, they would have to be invited to 'come in from the cold', and Ofcom would have to have a set of licensing policies that were sufficiently lax to permit 24 stations all playing the same kind of electro-shed, play-house or garage-door music onto the dial. It is almost certain that the existing legitimate stations would object to this on the grounds that it would provide unfair competition. But the fact is that such competition already exists on the FM band, and at least if it were done under a licensed framework, there would be some control over what went on, and thus greater protection of the existing 'big boys'.

Maybe Ofcom could take a leaf out of the book of the Lebanese regulator (the TRA) who offered all unlicensed FM operators (which was a large proportion of the country's stations at the time), a licence, if they came forward and provided the necessary details of their transmitting facilities (power, frequency, antenna height and so on). Most stations did this, wishing to gain legitimacy for their service. As soon as they did, however, the TRA could begin to change frequencies, powers and so on to bring the stations in-line, through a proper legal framework that allowed them to inflict penalties if people refused.

pirate surrenderAnother model might be for Ofcom to licence small-scale DAB operators, but not to set any criteria over which stations are carried on the multiplex, other than their normal broadcasting code which is designed, for example, to stop politically motivated stations from using the airwaves in an partial way. Other than a bit of swearing here and there, most pirate stations would probably already meet most of the rules. This is not dissimilar to the way in which Ofcom licenses digital television, with multiplexes being awarded to companies who are then largely at liberty to select which programmes they include.

In either of the above cases, whether the idea that Ofcom could have an 'amnesty' for pirates, if they agreed to go onto small DAB multiplexes, or if the operation of the DAB multiplexes were made flexible enough to accommodate pirate stations being on them, there might be a sufficient increase the listening to DAB services such that the necessary 50% switch-over threshold is reached sooner rather than later. A 'win-win' situation?
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