Slashdot Mirror
O'Reilly's Antenna Shootout
nickynicky9doors writes: "From Rob Flickenger O'Reilly Network's Systems Administrator :
'Gregory Rehm hosted an Antenna Battle Royale between a Lucent popsicle stick, a couple of Pringles Cans, our Coffee Can, a Hunt's Tomato Sauce can, and a 40oz can of 'Big Chunk' beef stew. Who was the winner?'" Let's just say it doesn't come loaded with saddle-shaped styro-chips.
yes, the regulations are all about ERP(effective radiated power), not how much power your putting into your feed line. For many services this means that if you are running the maximum power, and add an antenna with more gain, you must drop your power. But for point to point networking in the 2.4ghz ISM(industrial, scientific, medical) band you are are allowed to use directional antenna for point to point communictations, upto i belive 6db gain and still run maximum power. Above that you must drop your power, but the requiered drop is something like 1db less power for every 2db of gain, so it's not to bad. Keep in mind that my numbers are not correct.
But the other thing to consider is that i think most cards dont run the maximum allowed power, so you should be able to use a high gain antenna with any problems.
ALso, keep in mind that the regulation allowing high gain antennas without lower power specifies point to point communications, so that 20db gain yagi ontop of your car might not be legal.
The other thing to remember with 802.11b, is that 802.11b isnt the only thing on the 2.4ghz ism band, and ISM isnt the only thing 2.4ghz is allocated for. There is also amatuer allocation covering the same frequencies, and there has been at least on case of someone having to shutdown an 802.11b network do to interference it was causing. Also always keep in mind
-- free as in swatantryam - not soujanyam.
He makes a big deal about which antenna had the most raw gain. This is only *half* the story. He only makes some vague hint about needing to consider the receiver noise but doesn't consider it like it needs to be considered. Antenna reception is rated in G/T (gain over noise temp). The story talks about G but no one knows what T is. Thus G/T is unknown and his conclusions are somewhat less than useful. A big signal is of no use if it is drowned in a heap of noise.
Yoghurt
100 dB above what reference? A certain number of dBs of signal doesn't mean anything unless you specify a reference level, like 1 mW or such. Decibel readings are a relative measurement only. They are based on the base-10 logarithm of the ratio of two absolute measurements. I can't imagine that the ratings that you may quote are in dBmW, because 100 dBmW is 10 megawatts!