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Aussie Research Company Brings Wi-Fi To TV Antenna
joshgnosis writes "The CSIRO has unveiled new technology that could bring internet to people in rural or remote parts of Australia using their existing TV antennas. Analog TV signal is set to be switched off in 2013 but this technology could see the spectrum used to deliver internet straight into people's homes through their TV antenna. Gartner expert Robin Simpson told ZDNet Australia that this would make it much easier for companies to get new customers. 'What appeals to me about it is that it re-uses existing infrastructure, all of the competing wireless technologies tend to use high frequencies and therefore require new base stations, new spectrum and new receiving antenna infrastructure as well,' he said. 'The fact that they're re-using the analog TV stuff gives them a much easier market entry strategy.'"
I would think that while you could easily receive the signal, transmitting back to the tower would be a problem since TV antennas were designed to be receive only.
Or do they plan to do a satellite-TV type thing where upstream is a modem and downstream is the wireless? Downloading family pictures takes 2 minutes, uploading 6 hours.
Probably upload via phone modem...
Ham radio guys know you can transmit a couple watts thru a typical TV antenna installation.
Issues:
1) The 75 ohm to 300 ohm balun won't survive more than a couple watts. Low power on the HT should be fine. Use 300 ohm twinlead and you can shove a hundred watts thru a typical TV antenna.
2) Terrible gain per pound or per sq foot of wind load. All that aluminum is for wideband gain as opposed to narrow band gain. You'll be very displeased with the performance compared to a "real ham radio antenna"
3) No inline booster amps for obvious reasons.
Biggest problem is legal, at least in the US, no unlicensed intentional radiators at any power level allowed in the TV bands... Going to take FCC rulings, maybe congressional bills. Probably just as bad in Australia.
"Science flies us to the moon. Religion flies us into buildings." - Victor Stenger
The return path isn't omni-directional -- the TV antenna at each home will be focusing most the energy straight towards the tower. Also the bandwidth of the data signal will be much less than a TV signal, so it won't require nearly as much power. Such a link could be done with 10mw but it will be quite slow.
You're not talking about 1980's Teletext, are you? An achingly slow way of distributing 1kB information pages by transmitting data during the vertical blanking interval. It was incredibly popular in the UK for television listings, news and (strangely) holidays.
Also made famous by the BBC Micro, which had a teletext chip in it which could be used as an alternative to its framebuffer graphics modes. As teletext allows you to do eight colour text and primitive block graphics while only using 1kB of video RAM, it was really, really popular, which is why a whole generation of programmers today associate 129 with 'red' and 141 with 'double height'. (I wonder if you can still get the video decoder chips used? They'd be great for homebrew computers.)
They're aiming this at rural areas, and they will almost certainly be using more transmitters with a lower power than TV, so 10,000 people is probably a lot more than you'd actually get per transmitter. That's a small town, while this is more likely to be used for a village plus surrounding area. And don't forget that that 256Kb/s figure is guaranteed bandwidth. As long as they have some kind of channel negotiation, individual users can grab more bandwidth when they need it as long as the other users aren't all downloading at the same time. Typical Internet usage is full of idle periods and bursts, and as long as they aren't all bursting at once they can probably get 2-10 times that much without any problem.
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An antenna is an antenna. The only thing you have to do is tune it to the correct frequency, and that's trivial; a matter of length.
There's no difference between an antenna for recieving and one for transmitting -- it's just a piece of the right length of wire. Notice that your cell phone only has one antenna, not separate and transmit antennas?
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Everything is an antenna, it's a matter of matching the wavelength efficiently to the tranceiver source and the directional relationship between transmitter and receiver. A TV antenna is like any other antenna in that the best reception and transmission have to do with the little tynes or rods or radiators on them matching the exact frequency desired. The old set top monopole and dipole antennas can be tuned by moving the collapsing rods to match the desired frequency. Barring that, it's not as efficient. Sometimes a quarter wave, half wave, eigth-wave can do the job, but tuning it helps.
Once you use an existing TV antenna to transmit, you're captive to the wavelengths (rod lengths) it has; there will be some efficiency but a lot will be lost. Then, the problem becomes having sensitive receivers upstream to be able to correctly discriminate the desired signal-- and make sense out of it at distance.
It's at this point where I think things go awry, in that the electronics used to send a signal are designed to do so radially with perhaps megawatts to get to their desired TV antenna to produce an adequate picture. A couple of watts might get you quite a ways (125mi+) with highly tuned directional antennas (like the famous WiFi Pringle can projects adjunct to DefCon meetups) but these aren't highly tuned, directional antennas. A couple of watts gets you to the end of the block on a good day.
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The "Company" in the title is misleading, too. CSIRO is a government agency, akin to the USGS or NASA.