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That is one of the most ingenious sites I have ever seen those guys in NZ
are quite creative! Xanax. "DaveC" wrote in message al.net... Working with 2.4 GHz 802.11b wireless signal. Using USB adapter (one of those thumb-sized products) and an old 18-inch satellite TV dish. Calculating dish's focus point as f = ( d^^2 ) / ( 16 * c ) f = focus point above center of dish d = diameter of dish c = depth of dish at center With a circular, symmetrical parabolic dish, I presume that the focus is directly above the center. I've located the tiny antenna within the adapter as close to this point as i can. ( Odd thing about this dish -- this one is a DishTV brand -- is that in the original design for satellite reception, the driven element [ the "can", the input to the LMB ] was located low on the dish. In other words, the focus used in this design was off-center, about 30 degrees below the center axis of the dish. This would mean that aiming would be off-axis, too, yes? What is the reasoning behind this design? ) Setting up on the roof, finding the wireless access point's signal, I moved the wireless adapter around the focus point a little to maximize signal strength (I use the word "maximize" loosely...). I then aimed the dish around in the general direction of the access point, looking for a leap in signal strength (using a signal strength utility program to verify my aim ). I find 2 things: 1. It doesn't really matter where I point the dish. The signal varies a little bit when I approach the direction of the access point, but no "leaps and bounds" in the signal strength between being "dead on" and way off. 2. I pick up signals that aren't even in the direction of the access point. I tried rotating the dish on its axis to account for polarity mismatch ( would this really be an issue? ). No joy. The wireless adapter can receive signals well, generally, w/o a dish, but because of my location, reception of the desired signal is not great. I'm aware that reflections can be strong from nearby objects, so that could account for some pickup of signals in directions other than from their origin. Also, I suspect that the shallowness of the dish is a contributor. But the lack of directionality of the dish, in general, has me stumped. Have I miscalculated the focus? I understand that the ratio of focus-to-diameter of the dish is important; for 2.4 GHz, is best in the 0.25-0.55 range (this one is 0.69). Is this contributing to my problem? I used this web page as a reference: http://www.usbwifi.orcon.net.nz Any help would be greatly appreciated. If this is off-topic for any NG here, please let me know what is a more appropriate forum. Are there mailing lists for such topics? Thanks, -- DaveC This is an invalid return address Please reply in the news group --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.682 / Virus Database: 444 - Release Date: 12/05/2004 |