Australia's Outback Could Get Web Via TV Antenna 121
disco_tracy writes "Australia began switching off its analog TV signals in June and the transition to digital-only transmission is expected to be complete by the end of 2013, five years before the roll out finishes for the NBN. The leftover analog spectrum could be used to deliver Internet to people living in remote areas. Unlike 3G networks, which lose download speed with more users, the analog signal would provide a consistent speed no matter how many users there were."
Power... (Score:4, Interesting)
The ability to transmit VHF (TV) into the hinterlands had as much to do with multi-kilowatt signals as it did with frequency. Pump 60 Kw into a 2.4 GHz wifi transmitter with a good directional antenna placed on a high tower and I'll bet the punters in the outback can find a working hotspot -- probably one in China at that power.
Re:Stupidest idea ever (Score:4, Interesting)
Geez, I wish the operators of the thousands of amateur radio repeaters on frequencies not so far from TV freqs knew what you know about RF. They would know that the installations they have been using for about 40 years now can't possibly work! How silly of us to have (for decades) successfully used systems which receive a weak signal only a few khz away from a strong signal being broadcast on the same antenna at the same time.
Well, yes and no. (Score:5, Interesting)
I suspect the GP was engaging in a bit of hyperbole with the "China" reference, but reception of Chinese VHF TV signals in Australia is in fact possible on rare occasions [iprimus.com.au] via the ionosphere [iprimus.com.au]. The propagation modes usually involve simple refraction from the E layer [wikipedia.org] or F layer [wikipedia.org], although occasionally more exotic types of propagation, such as trans-equatorial propagation [wikipedia.org] ("TEP"), occur. However, these all fall into the category of anomalous propagation, occurring for a few hours per month or year and, while interesting phenomena in their own right, aren't suitable on which to base one's daily Internet service.
It is also true that ionospheric propagation of 2.4 GHz signals is unknown. However...
There are propagation modes that favor the higher frequencies over the lower ones. Tropospheric propagation [wikipedia.org], for example, is much more effective at 2.4 GHz than it is at VHF, and can occur at all parts of the sunspot cycle, since it depends on weather conditions instead of the ionosphere. For example, Table 2.1 in this article [df5ai.net] shows propagation from California to Hawaii on 2304, 3456, and even 5760 MHz via a well-known tropospheric duct. (See also this discussion [df5ai.net] on the relevance to trans-Australia propagation.) Paths in excess of 6000 km (Western Australia to Reunion Island, off the east coast of Africa) have been reported. But again, this is anomalous propagation, unsuitable for daily Internet service.
The GP has a point about transmitted power. VHF TV broadcast stations have effective radiated powers ("ERPs", defined as their transmitted powers multiplied by their antenna gains) measured in the hundreds of thousands to millions of watts, as well as high antenna sites (on towers), so it's a bit unfair to compare VHF TV reception ranges to those of 2.4 GHz Wi-Fi systems.
The main advantage of the proposed system is that the users, in remote sheep stations, won't have to replace their existing VHF TV antennas, which would otherwise be a significant financial investment (and that the system would be point-to-point, rather than point-to-multipoint, which enables frequency reuse without loss of bandwidth). Were this not the case, it would be clear to most RF system designers that a microwave system would be superior to the VHF system. Not only is more bandwidth typically available (remember, there are no competing services in the outback), but a 2.4-GHz antenna the same physical size (strictly speaking, having the same effective area) as the VHF TV antenna would have substantially more gain: The gain of a parabolic dish goes up as the square of the operating frequency [wikipedia.org]. Operating an antenna at 2.4 GHz instead of, say, 60 MHz (in the VHF TV band) would result in a gain increase of 1600, or 32 dB. If it had 18 dB of gain at VHF (a pretty decent TV antenna), it would now be 50 dB at 2.4 GHz. (This is why point-to-point microwave systems were used before they were overtaken in the bandwidth race by optical fiber.) This additional 32 dB of gain would greatly increase the range of the 2.4 GHz system over the VHF system, and would be available all the time -- making for a suitable Internet connection. In fact,
...but the Internet is bidirectional. (Score:4, Interesting)
So how does this allow the subscriber to send data? Does everyone have to have a megawatt transmitter in their home?