The 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.
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).
The 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!
Friday 1 April, 2016, 10:03 - Radio RandomnessDespite 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.
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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.
Take, 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.
If 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 Longitude (e.g. 108.9E)||Antipodal Latitude|
Thursday 24 March, 2016, 12:50 - Broadcasting, Pirate/Clandestine, Spectrum ManagementThis week, Wireless Waffle took a rare trip to the far reaches of the UK. Or Birmingham to be precise. To be even more precise, the motorways surrounding the UK's second city, whilst en route to elsewhere. The journey gave the opportunity to do a bit of tuning around the FM band to see what's happening in the West Midlands these days. Other than the various commercial stations (including local regional stations Touch FM and Free Radio), and a handful of community stations (including some in neighbouring Coventry), the thing that was most different to the airwaves in the South East was the absence of much in the way of pirate radio.
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Only two pirate stations were heard during the journey:
It's probably about time that Wireless Waffle stopped banging on about pirate radion stations, after all it's now just a year shy of the 50th anniversary of the Marine etc Offences Act whose purpose was primarily to bring down the original pirate stations of the day. The fact, however, that such stations continue to abound suggests that the mainstream UK radio market is failing certain sections of society, which appear to be certain ethnic minorities (Caribbean, African and Turkish in particular) and those who like gruff-beat, wacka-jam and gutter-beat music (or genres with similiarly bizarre titles). It's also clear that Ofcom's efforts to take the stations off-air is not having the desired effect (meaning 'to force pirates off-air').
Information on enforcement activity released by Ofcom under the freedom of information act reveals, for example, that between 2007 and 2012, Kriss FM had its transmitters taken off-air by Ofcom 17 times and its studios raided 6 times. Hot92 had its transmitter raided 42 times and its studio raided 3 times. Sting had an astounding 60 transmitter raids (and 3 studio raids) over the same period.
We recently discussed the idea that pirate radio could move to small-scale DAB radio services, or conversely that the closure of regular FM services might open up the FM band as a playground for even more pirates. But could there be yet another option... If Ofcom were to cease all enforcement activity on pirate radio (except in casese where it was causing interference to safety-of-life services) and let the illegal broadcasters run riot, the amount of intereference they would cause to legitimate stations would increase and this might be the incentive needed for those listeners to finally go out and buy a digital radio! So instead of continued enforcement, why not leave the pirates alone and see if that has the desired effect (in this case meaning 'forcing a move to digital radio').
Friday 11 March, 2016, 13:34 - Radio RandomnessWireless 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:
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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.