Build WiFi Range Extender from 18" Parabolic Dish, construction pictures + instructions
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Posted by on April 18, 2007, 5:50 pm
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Build A Tin Can Waveguide WiFi Antenna In One Hour. Then put it on a 18" inch direct tv dish, (optional). No coax signal loss. I use a USB device on antenna, so only a usb cable feeds my computer. With 16' USB REPEARER CABLES end-to-end you can run 80 feet of cable without loss. Complete instructions. This Powerful wlan antenna REALLY KICKS BUTT!! Here is my version of the dish conversion to wifi range extender-> http://www.findmorecollectibles.com/wifi.html enjoy, ac6ts | ||||||||||||||||||||||||||||
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Posted by Jeff Liebermann on April 18, 2007, 9:54 pm
Please log in for more thread options On 18 Apr 2007 14:50:16 -0700, ac6tsxx@gmail.com wrote:  Maximum gain for a 0.6meter diameter dish: gain = 9.87 * Dia^2 / wavelength^2 * (feed efficiency) gain = 9.87 * 600mm^2 / 125mm^2 * 0.4 gain = 91 dBi = 10 log(91) = 19.5dBi The 40% efficiency (that's the 0.4) is probably optimistic. However, that's the best that can be done. With a mismatched feed (your USB contraption), you'll be radiating much of the signal into all manner of undesireable directions, with very little hitting the dish and being reflected in the desired direction. That's why feed point "illumination" is important. Ideally with a properly matched feed, you'll get the same gain in xmit and recv. However, with your USB device feed system (an almost hemispherical feed pattern), all of the signal arrives at the feed in receive, but much of the signal goes nowhere useful in xmit. So, you'll get somewhat less than the theoretical 19.5dBi gain in receive, but xmit will be far less gain. Might was well guess how much less. Assuming a hemispherical pattern from the USB antenna, only about 10% of the RF hits the dish. The rest goes off in useless directions. So, 10% is: loss = 10 log(0.1) = -10dB So, my guess is that the antenna gain in xmit is about: 19.5 - 10 = 9.5dB Yech. (I can produce a more accurate number for the 10% later but I don't have a DBS dish to measure handy right now). -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 jeffl@comix.santa-cruz.ca.us # http://802.11junk.com jeffl@cruzio.com # http://www.LearnByDestroying.com AE6KS | ||||||||||||||||||||||||||||
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Posted by Jeff Liebermann on April 18, 2007, 10:02 pm
Please log in for more thread options On Thu, 19 Apr 2007 01:54:47 GMT, Jeff Liebermann Sigh. Sorry, I goofed. I was looking at a variety of DBS dish reflectors on other sites and got your construction mixed with another one that did NOT use a can type feed. My comments about different gain in xmit and receive apply only to building it without the tin can. If the can feed illumination pattern is reasonably well matched to the diameter of the dish, the tx and rx gains should be the same. My appologies for the wrong info. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 jeffl@comix.santa-cruz.ca.us # http://802.11junk.com jeffl@cruzio.com # http://www.LearnByDestroying.com AE6KS | ||||||||||||||||||||||||||||
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Posted by on April 18, 2007, 10:36 pm
Please log in for more thread options The tin can was cut to 3-1/2 inches, which seems too short to me. with a 4" diameter can, I think the radiator should be at 1.7", but I would like to see the can at 5.5" as a standalone can. Should the radiator be at the focal point, or the mouth of the can (properly sized for its own radiator)? And where might we assume that the radiator is on that adapter? It looks like it might be in the middle of the bore, which is good, but that's an awfully large hole in the side of the can, which I thought Jeff didn't like in building a wire cantenna. Bob Alston's coffee can http://members.cox.net/tulsaalstons/Computer.htm Clarence Dold's coffee can http://www.rahul.net/dold/clarence/usb-can/im000742-800x600.jpg -- --- Clarence A Dold - Hidden Valley Lake, CA, USA GPS: 38.8,-122.5 | ||||||||||||||||||||||||||||
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Posted by Jeff Liebermann on April 19, 2007, 1:12 am
Please log in for more thread options On Thu, 19 Apr 2007 02:36:26 +0000 (UTC), dold@84.usenet.us.com wrote: 3.5 inches might be a good length. With dish feeds, the idea is to design the feed illumination angle so that it exactly covers the dish area. No more, no less. In this case, there's no interest in maximizing the gain because the dish does most of that, not the feed. However, if he were trying to squeeze every last dB of gain out of the antenna, feed gain would be important. See: <http://www.w1ghz.org/antbook/contents.htm> <http://www.w1ghz.org/antbook/chap6-3.pdf> See 6.3.1 above for details on the spillover (overspray) problem and the introduction at: <http://www.w1ghz.org/antbook/chap6-0.pdf> for general clues. New stuff: <http://www.w1ghz.org/antbook/conf/high_efficiency_prime_feeds.pdf> Just inside the mouth of the can is at the focal point. The exact location is the "phase center" of the feed. See fig 6.1-1 in: <http://www.w1ghz.org/antbook/chap6-1a.pdf> I gave up trying to calculate the exact location and just move the feed in and out until the gain is at maximum. I have a DWL-120 (somewhere) which is what the author used. It looks like a loop antenna, but it's not. It's just a 1/4 wave (3.13cm) piece of wire inside the plastic loop. The problem is that I don't remember which side of the loop had the antenna. If I get ambitious, I'll tear it apart and see. Meanwhile, you're correct. The antenna is *NOT* in the center of the loop and therefore in the canter of the can. That will cause a lopsided illumination pattern. My (paper) coffee can: <http://802.11junk.com/jeffl/antennas/coffee2400/> I could probably scale the model to match the tin can in the DBS dish construction, and see how it looks. (yet another project). My hacked version of Ivor Hewitt's Excel spreadsheet for generating an NEC2 "card" suitable for feeding to 4NEC2 antenna modeling software: <http://802.11junk.com/jeffl/rf-calc/Coffee-can05.xls> Unfortunately, it has some problems that I've been too lazy (or too inept) to fix. Caveat Emptor and let me know if you find any (more) bugs. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 jeffl@comix.santa-cruz.ca.us # http://802.11junk.com jeffl@cruzio.com # http://www.LearnByDestroying.com AE6KS | ||||||||||||||||||||||||||||
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>18" inch direct tv dish, (optional). No coax signal loss. I use a USB
>device on antenna, so only a usb cable feeds my computer. With 16' USB
>REPEARER CABLES end-to-end you can run 80 feet of cable without loss.
>Complete instructions. This Powerful wlan antenna REALLY KICKS BUTT!!
>Here is my version of the dish conversion to wifi range extender->
>http://www.findmorecollectibles.com/wifi.html