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Quiet Cellular Antenna Tech To Boost S. African SKA Bid 38

slash-sa writes "Two South Africans have given their home country a boost with its Square Kilometre Array (SKA) bid by inventing cellular antenna technology which reduces 'noisy' emissions from cellular base stations in the area. They reduced emissions by using an antenna based on phased-array principles, providing omnidirectional coverage but also blocking the RF transmissions along a single direction (that would correspond with the bearing of the SKA core site). The antenna has been tested and performs extremely well. Trialling measurements have shown that the RF signal levels at the proposed SKA core site can be reduced significantly, while at the same time, much of the original GSM coverage can be retained."
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Quiet Cellular Antenna Tech To Boost S. African SKA Bid

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  • by SevenTowers ( 525361 ) on Saturday October 29, 2011 @04:43AM (#37877270) Homepage
    science still gets some funding. Amongst all the cuts we've seen in the past years, this is excellent news!
  • What is to stop the australians from using similar things to this?

    • Australia would be welcome to do something like this... I'm a South African EE student at the moment, I'm working towards an SKA related project, and whether or not South Africa is chosen ultimately, we have our own radio telescope plans, so this would be useful anyway.

      The SKA is about international collaboration, AFAIK. It's good for countries to share inventions.

    • Re: (Score:3, Informative)

      by sirlark ( 1676276 )
      Apparently one of the big advantages the Australians have in the bid is that their site already has significantly less RF interference because of it's relative remoteness and much lower surrounding population density. However, that remoteness is a downside too, as it makes construction and supply costs much more expensive. This technology could really improve South Africa's chances, because apart from RF interference, they seem to have a stronger bid. The Karoo, being less remote, reduces costs for building
      • by thegarbz ( 1787294 ) on Saturday October 29, 2011 @08:57AM (#37877998)

        However, that remoteness is a downside too, as it makes construction and supply costs much more expensive.

        This is actually one of the real forte's of Australia's construction force. Our many remote mining and gas projects which create a local town to sustain the business have basically trained a contract workforce and vendor supply chain easily capable of building massive projects in the middle of no where.

        Though this is a double edged sword. The last gas plant I worked in recently had massive troubles finding qualified welders to work during their maintenance shutdown due to the amount of work going on around the country sucking up local resources.

        • the company pay to train people

          • That is not how construction works, and it's also not how training works.

            It is incredibly rare that an internal company workforce will build a new project, it is almost always an external contractor which is bought in. A company who wants to build a gas plant has zero incentive to train people to build one as when construction is finished they are no longer needed and need to be replaced with a workforce of different qualifications (these often then do get trained inhouse).

            Additionally a contracting company

        • This is actually one of the real forte's of Australia's construction force. Our many remote mining and gas projects which create a local town to sustain the business have basically trained a contract workforce and vendor supply chain easily capable of building massive projects in the middle of no where.

          Fair enough, but it still costs more... that cost is presumably hidden in the more expensive labour costs, exchange rates, etc. Not arguing that the Aussies can't do it, just that they're more expensive than the South Africans. Also, building a town around the SKA is precisely want should be avoided surely?

    • Nothing. But as other have mentioned, it is not really necessary. There are very few registered transmitters within 100 km: [] More info can be found here: [] And transmission limits here: [] And my rough estimate of Australia's SKA site: http://maps.googl []
  • by Anonymous Coward

    Since the site is in Geraldton, which doesn't have a lot of GSM coverage anyway and very few radio transmissions, since it's so sparsely populated.

  • by nroets ( 1463881 ) on Saturday October 29, 2011 @07:13AM (#37877602)

    Getting the antenna deployed is another matter. For example ICASA has serious corporate governance problems [].

    I live in South Africa and I regularly pick up high power WLANs in my neighbourhood. And I suspect many of them are used to carry CCTV signals or to bypass the expensive telecoms operators. The public is sympathetic to these cause. So compliance with government regulations will not be very high.

  • It's a neat idea, but it doesn't solve the problem of the phones themselves being transmitters!

    • The root cause of the problem is that cellular phones are about the only reliable communications method used by the farmers near the proposed site. Use of phones on the site itself isn't a problem as the operational rules would forbid it, but the towers needed to support the farmers would interfere.

      By creating an antenna that can blackout a narrow sector - the site - while not affecting signal strength for the farmers, they eliminate the issue of interference without forcing the farmers to lose reliable co

  • I did RTFA, but with my limited knowledge I didn't see what's unique with their use of phased array antennae.

    Anyone able to elaborate? Is it unique because it's in the GSM band? Because it blacks out a very narrow area?

    • There is nothing unique about phase array antennas, or anything challenging about applying them to the GSM band. It is probably unique since the technology is only required when providing farmers mobile phone access close to large sensitive radio astronomy telescopes.
  • by rgbatduke ( 1231380 ) <> on Saturday October 29, 2011 @10:59AM (#37878860) Homepage
    Every cell phone tower in the US has access to extremely high precision time signals via GPS (and indeed, most of them function as secondary GPS locators by effectively forwarding that signal plus tower location data for phone "GPS" which isn't). Every cell phone tower is basically a big antenna. Every cell phone tower has excellent signal connectivity (usually fiber, sometimes microwave) to a communications network that can carry the signals they receive at any particular frequency, convolved with a universal time reference frequency synchronized by means of the aforementioned GPS, to a large processing station. Hence it is absolutely bone-simple to turn the entire network of existing cell phone towers into one great big radiotelescope.

    The cost of doing so is almost certainly going to be a tiny fraction of the cost of building an actual devoted function radiotelescope. I had a student estimate the cost per tower to be in the ballpark of $1000 US for a local computer and sundry electronics, probably less purchased in bulk. One could very likely get the tower owners to donate at least the access to the radio signals (basically costs them nothing), a place to site electronics (ditto), and with luck even a channel and some bandwidth to permit the upload of x-hours of recorded phase locked signal in off-peak bursts as part of their "public service" requirement.

    The additional benefit is that one ends up with a radiotelescope that spans a continent -- an aperture several thousand kilometers across, with hundreds of thousands to millions of towers contributing. The resolution would thus be orders of magnitude greater than any of these toys that they are trying to fund and the sensitivity (proportional to N^2) would be MANY orders of magnitude greater as well. In fact, one could probably build arrays that spanned continents and turn the entire surface area of the earth into one big radiofrequency "eye" that can be turned not just anywhere but everywhere 24x7 -- the towers basically record a high resolution hologram of the night sky and one can "look" in any direction you like within any single dataset by simply adjusting the phases of the recorded signals appropriately in the decoding. That is, one doesn't have to devote the towers to looking in some particular direction, one can look in all directions at once and choose what to actually look at in detail in the step where the signals are decoded and recombined with appropriate phase delays.

    This will never get funded, of course -- it isn't "big science" in any visible way. Or rather, perhaps it already has been funded, because it is one of the few ways I can think of that one could provide an ABM defense with a universal direction "eye" with sufficient resolution to locate an incoming warhead, and (by using the entire array as a phase-locked TRANSMISSION array) one might even be able to deliver a megawatt or so of power of microwave energy directly onto the missile itself and burn it out. Of course, if this is true then I guess I'll soon have somebody knocking on my door for publishing this on /., but so be it.

    • You would need to add large, stable, steerable, and extremely sensitive dish near each tower because the cellular antenna and receivers aren't even close to sensitive enough. The RF from the tower would overpower the receiver and electronics for the dish. That's the core of the problem they're trying to address in SA.

      • Actually, this is not true. A million towers -- squared. The signal is there, only it is buried in the noise. With one tower you can't extract it. With ten towers (directionally phased) you basically boost the signal to noise ration by 100 (and probably still can't extract it). With a million towers, you increase (directionally selected) signal to noise by a factor of 10^12. That's the whole point of radiotelescope arrays. For small arrays, with only 1000 or so receivers, sure, you need to bump signa
        • Signal-to-noise ratio. Even with a massive array of dipoles, trying to pick a signal with less than 10^-9 relative strength is essentially impossible. Assuming 32-bit sampling (which is what they're using in state of the art radio astronomy), you've got only a 4B range, and the signals you're looking for a less than 1/1B of that. There isn't enough remaining sensitivity to differentiate it from noise and interference that are thousands, millions, and billions of times stronger. The cellular signals and othe

    • This will never get funded, of course -- it isn't "big science" in any visible way

      DARPA does love crazy game changing ideas like this... but you'll have a tough time getting this one past a technical review since you appear to be unaware of some serious technical issues.

      Every cell phone tower is basically a big antenna.

      It really isn't. A cell phone tower is a just a tower with many directional antennas on it. Typically antennas are installed in a trio each one covering 120 degrees, to separate the three "

      • Sure, but all of those issues also exist (except for the radio interference issue, which exists but is smaller) for any array of dipole antennae including the ones that are part of the SKA. However, I wouldn't argue that the cost might be higher than my student's guess -- it was predicated on various things and as you're pointing out, "reality" might be different on some of them, although the idea itself in principle would work with some tweaking.

        What I suggested to my student was that he/we write a pr
    • GPS does not provide a good enough time reference for an application like this. Typically you need a hydrogen maser; these cost about $300K. The problem is that GPS has pretty poor short term stability - about +- 20 ns at 1 s for a low cost timing receiver. Averaged over one day GPS gives you a decent frequency reference but to average, you need another oscillator like a rubidium atomic clock. The rubidium gives you better short term stability and then you improve its long term stability by comparing it
      • Well, OK then. Yes, stability is key, although I fail to completely understand why they don't put high precision and stable clocks in the GPS satellites if they are going to put it anywhere, since putting a $300K clock at every tower would, no doubt, raise the cost a bit...;-)

        • Not quite sure what you're saying. GPS satellites do have good clocks on board - rubidium and cesium atomic clocks - and these clocks are steered from the ground by a very large ensemble of atomic clocks including hydrogen masers. The proBlem is transferring this to a ground station. The ionosphere and troposphere introduce short term noise that degrades timing references that you can derive from GPS. GPS broadcasts information that allows correction for these effects but this is of course via a model. You
          • Oops, now I see what you meant. When I said that GPS was not good enough for this application, I was referring to VLBI, not synchronizing a phone network.
            • Yes, well I have given up -- you and others do indeed seem to have thought things through more carefully than I have so far, which is to be expected I suppose but it's disappointing that it won't quite work, if only because it would make such a hell of an array if it did. But between clock problems and signal problems, looks like it almost only counts with hydrogen bombs and hand grenades, not cell phone tower radiotelescopes. Sigh. Hope I wasn't too obnoxious in my misdirected enthusiasm...;-)

  • I am not quite sure how this will influence the bid? It seems to be yet another PR attempt to try and convince the uninformed of the benefits of a R2m investment in SKA SA and MeerKAT.
    • It is useful because it will eliminate a possible source of interference at the Karoo site that isn't present at the Australian site without shutting cellular phones down over a too-wide area.

      And do I sense hostility for our country getting the SKA or are you merely annoyed at having to convince the ignorant of its obvious benefits?

      • If those guys have come up with a technology that will eliminate the interference, I would be really impressed. I can't imagine they will get more than 30-40dB down from the "omnidirectional" base station antennas. MeerKAT (let alone the SKA) will be an extremely sensitive instrument, able to "detect a cell phone on the moon", so maybe you wont saturate your receivers, but you always going to see and will always need to deal with it if you going to be looking comic signatures in your mobile bands. I think
        • Somebody Please!

          calculate how far away (skyward) the SKA could actually hear a GSM phone!

          Probably way past the moon, but I could be guessing...


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