Electronics > RF, Microwave, Ham Radio
First DIY dish (WOK used as reflector), need a little help
rwgast_lowlevellogicdesin:
So I am setting up a small dish beam 2.4ghz wifi up a mountain behind my house to an ras pi, Acually the dish will most likely be connected to the PI and beamed down the mountain to a router running custom firmware with another homemade directional antenna, hoping I can get away with something much smaller on the router end.
Anyways the dish is is simple as I said I want to use it for wifi, and I may use it to some experimentation with other microwave frequency's by swapping the feed. Now I have seen people do all kinds of weird stuff online like taping a USB wifi card in front of a noodle strainer and claiming to get good results. Well I bought a 4 dollar WOK at wal mart and I would like to make the dish as efficient as something made from a WOK can be...
First of all this is where I am so far
A while back a guy I did some work on a lot of audio equipment for a guy, and besides payment he gave me four of these mic stands that make nice booming tripods for antennas, Im currently using two other ones for yagis. So you can see how I mounted the walk, first off is the fact that I punched that hole in the very center of the dish stupid? I mean that is the point where most of the RF energy is right, I plan to do this as an offset and I am under the impression the whole dish collects RF and then it is focused at the feed, so im not to sure how important the center of the dish is.
Next the WOK was coated in teflon, which isn't a suitable conductor so Im stripping it with a drill and wire brush. I have to do some electroplating on a bunch of soldier tips soon, I was wondering if when I do the copper coating on the tips if I should throw the WOK in there... I am not sure what kind of metal the WOK is, it is magnetic so not aluminium, but to get the most out of it I would think plating it in copper (or silver if I could afford that) will give the collector a bit more oomph. Im not sure if that is over thinking and over engineering but I am already plating stuff so its really no big issue to do the WOK at the same time.
Im a bit unsure of one more thing when it comes to dishes... so you build your feed and the coax runs to it with the braid connected the ground part of the dish feed or antenna, and the signal part connected to the biquads or helix or whatever feed design you choose. What about the acuall dish though, should this either connected to RF ground or earth ground? Usually in a directional antenna the reflector is connected to ground, but I dont see that on dishes, or at least i haven't noticed it.
Lastly is there a good bit of software out there for simulating a parabolic reflector based on frequency? We all know any junk from a can wave guide to a WOK will work and even improve things, but it is no match for something proper... I think I have line of site to a friends house where I am going to put up a second remote controlled radio station, but he is pretty far maybe 15 miles or even a bit more. Like I said I think due to my house being at a higher elevation we can get line of site but Im sure a WOK is not going to do the trick to run a a full speed 802.11 G network between our houses.
wraper:
Wrong geometry to be useful.
--- Quote ---Next the WOK was coated in teflon, which isn't a suitable conductor so Im stripping it with a drill and wire brush.
--- End quote ---
:palm:
voltz:
This is a real 'thing'. Its called WokFi. https://en.wikipedia.org/wiki/WokFi
Get it right and you're looking at +10db gain.
A bit mad - and i like it :) good luck.
Howardlong:
Probably going to regret coming in here ;-) but I'll give it a shot.
First, old satellite dishes are two a penny these days. Most are offset fed, which means the feed doesn't obscure the dish. You really need about 2' or more at 2.4GHz. Properly setup, you can expect about 19-20dBi of gain.
Second, the Pringles can is the wrong size for 2.4GHz, it's too small. Anything that professes to "work" at 2.4GHz with this is in spite of the Pringles can, not because of it.
Third, for a feed to work you need to consider the depth of the dish and the illumination, including losses due to overspill or under illumination. Any feed you make needs to be made with care and positioned correctly at the focal point of the dish. In addition any polarisation you choose should match both ends. That's the physical side. The transmitter/receiver should be positioned at the feed point as feedline losses are pretty nasty in the GHz, and care should be taken in matching the antenna feed impedance to the transceiver's.
Here's a design I made many years ago, still very valid today. http://g6lvb.com/60cm.htm but back then WiFi was only just starting up, we had the band to ourselves.
Ian.M:
+1 for re-purposing an old satellite dish. You can also use a cantenna feed, but you need scalar rings to get the correct illumination. See http://www.qsl.net/ki7cx/wgfeed.htm
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