Who Needs a Satellite Dish When You Have a Wok?

An anonymous reader writes "Why pay $20,000 for a commercial link to run your television station when a $10 kitchen wok from the Warehouse is just as effective? This is exactly how North Otago's newest television station 45 South is transmitting its signal from its studio to the top of Cape Wanbrow, in a bid to keep costs down."

Re:Check the numbers

[Da Fokka]

If you'd actually read the entire article, which admittedly is a lot to ask, you'd have known that the local TV station used the same setup as an uplink, saving a cool $20.000

Tinfoil antenna would actually work

[maroberts]

As long as you make it the right shape, there's no reason why a tinfoil dish wouldn't do the job too.

You should see how thin some dishes on real satellites are.

Re:Missing link in TFA

[Anonymous Coward]

I think it's here :
http://www.usbwifi.orcon.net.nz/ [orcon.net.nz]

It doesn't matter that much

[Anonymous Coward]

The reflector does a couple of thing. The most obvious is that it catches the signal and focuses it on the antenna. The bigger the dish and the closer it is to a parabola, the more signal to the antenna. The other thing it does is to shield the antenna from noise. The antenna in the article seemed to be nested right inside the wok. So, the wok probably improves the signal to noise ratio (SNR) by at least double and maybe by a factor of three or four (or more if it's done right). That's very important. If your signal to noise ratio is good enough, you can use amplification to get the signal you need. If the SNR isn't good enough, then almost nothing helps.

The wok will give a useful increase in signal strength but a more significant improvement in signal to noise ratio.

Re:One of these will happen..

[frup]

This is in New Zealand... we're a little different to America

Re:So basically they made a loss?

[Svartalf]

It was Slashdotted [slashdot.org] in the past...

The links to part of the sites covering it are:
http://www.usbwifi.orcon.net.nz/ [orcon.net.nz]
http://www.stanford.edu/~jstockdl/tmp/usbwifi.orco n.net.nz/ [stanford.edu]

Re:So basically they made a loss?

[rudeboy1]

Depending on what frequency they were going for (I'm not up on NZ regs) transceivers can be found, as much as any broadcast/wireless parts, as scrap items in may places. I used to work at a wireless company here in the states, and transceiver arms were thrown out or given away with little care. It is conceivable that, given the ingenuity they showed in coming up with the wok idea in the first place, that they might have made the dish using spare parts.
    The dish really is a variable item. One could use a barbecue grill, if they were so inclined, (yes, you'd have to bend it to a reasonably concave shape, put that wouldn't be very difficult). As long as the "dish" relays the signal back to the transceiver/receiver (you simply make a triangle, determining at what angle the reflection of the signal from the dish will hit the antenna, make sure the dish has a linear curve to that angle/height... Remember making fire with a magnifying glass? Very similar principle), you could use any non-porous, reflective material.
    The only thing you would really have to buy new would be the coax RF cable (I say new because we are talking about weather treated cable, and if it has been lying outside unattached, you risk getting water inside the cable) and the (r)TNC connectors (depending on the connections... again, not sure how they do things in NZ)
    I agree with the posters above though. The expensive part of the equation is still the rackmounted hardware needed to tx/rx. That, sadly, cannot be made out of spare parts. Those suckers are expensive.
    Depending on local laws though, and depending on the amount of bandwidth they would need, it could be conceivable, if they REALLY wanted to save money, to make a wireless link using, say, 802.11N protocols, versus commercial microwave freqs. If they went that way, then, THEN they would be pinching pennies. (or quid... WTF ever) I would estimate that the whole rig mentioned above might cost around $500 (US) for both ends. Though I honestly couldn't tell you how they would convert their tv signal (more than just what you see on air) to a computer network protocol. I imagine they could think of something though.

Woks and their collanders, too

[DrYak]

Yes, woks can be good enough approximations of parabolic cross section.
And in fact, because of the wave-leght of TV, WiFi, Bluetooth, etc.. (signals in the GHz range have centimetric wave-lengths) their corresponding colanders too [orcon.net.nz] can be used as cheap antennas, and have the aditionnal benefit of having holes (they are basically metallic mesh) and therefore having less friction against winds (and lower risk of being blown away during a storm). /. have featured a few time ago an article about using wok colanders as dishes for Wifi USB dongles, and a several techniques to check is the parabolic approximation is good enough.
- one technique, which can be done in the shop before buying the colander, is to use a small chain whose shape when suspended at both end and check if shapes match (checking if the shape is "catenary")
- another is to cover the colander in aluminium foil and checking if a parallel light source (the sun) converge to one single point (where the USB dongle should go once everything assembled)

See /. article " 4km WiFi Range w/ $5 DIY Antenna [slashdot.org]". TFA is mostly the same idea but applied to a different signal in the same GHz range (microwaves).

Re:One of these will happen..

[BrokenHalo]

Don't you mean a little different *than* America?

No. He's right, you're wrong. Sorry.

Depends ...

[Physics Dude]

Actually the reflective efficiency depends on the power and frequency relative to the material conductivity and thickness. In order for a material to reflect an EM wave, it has to be capable of supporting the induced EM currents produce by the wave, and if I remember correctly, for maximum reflection the material has to be thicker than the skin depth [wikipedia.org] at that frequency. If the thickness is much thinner than the skin depth then minimal reflection will occur and the EM wave may pass through the material or, if enough energy is absorbed by the material in the form of induced currents, the surface may be damaged.

This is the effect you see with thin foils in a microwave oven, and has led to the extremely popular misconception that you can't put metal into a microwave. With a minimal bit of observation anyone will see that the entire microwave enclosure IS metal and reflects the microwaves just fine without significant absorption. The only problem is with thin foils which are incapable of efficiently reflecting the microwaves.

I haven't calculated how efficiently tin-foil might reflect the high power radio waves mentioned here, but wouldn't put money either way without checking. (I haven't yet read the fine article, so I don't even know what power levels we're talking about).