Hacking around with OpenSCAD I managed to make a cool looking offset dish antenna. Once I get around to it will try 3D printing it and covering with foil. Not sure how big to make it yet but will prob use a 3 turn helical as the detector part.
(http://s30.postimg.org/mdtvxusel/offset_reflector.jpg) (http://postimg.org/image/mdtvxusel/)
Attached is the OpenSCAD source if you are interested in having a go at it!
regards
Andy
Helical and base added and shape changed a bit to try to print in one piece on my printer. The 3 turn helical will be mounted onto a connector on a bit of GF tube. You can see the hole for the tube to slide into in the base of the reflector.
(http://s7.postimg.org/trha6dl9j/58_G_offset_dish.jpg) (http://postimg.org/image/trha6dl9j/)
EDIT: And as Rob Thompson pointed out, you need a helical of opposite polarisation to the one on your aircraft!
regards
Andy
This is pretty interesting, let us know how you get on. One of these would look cool on the side of a van :D
I imagine just a simple LHCP clover would suffice. The gain comes from the dish
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Cheers Steve! I keep hacking about with it. Might even try 2 dishes side by side, one for RC and one for video . I found a formula on Wikipedia (http://en.wikipedia.org/wiki/Parabolic_antenna#Gain) that says the gain for a 200 mm diameter 5.8GHz antenna at 50% efficiency would be around 70. (Which I think is 18.5 dB) With that sort of gain,you could go for miles on 25 mW :)
Rob. I reckon the signal that comes to the antenna is quite directional so a helical might be best. Anyway I find them easier to make (http://www.zoomworks.org/fpv/helical_antenna/index.html) :)
regrads
Andy
Could I suggest a £10 TBS patch type antenna?
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Quote from: rob.thomson on April 09, 2014, 10:51:20 AM
Could I suggest a £10 TBS patch type antenna?
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You mean instead of the whole dish antenna or instead of the driven element at the focus?
regards
Andy
The element at then focal point.
I just don't thing the helical will work as well as an patch of clover on the (lnb) head.
Spent a bit of time in the past playing with satellite dishes etc..
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Aha Your input will be greatly appreciated then !
According to the Wikipedia formula for a particular size of dish the gain is dependent on the frequency and works in favour of higher frequencies. For instance at 2.4 GHz the gain is only 12.5 ( 11 Db) In other words a small dish antenna looks really well suited to 5.8 GHz in particular :)
As for the driven element. I will make the attachment for it separate so you can stick different ones on.
However dont expect anything soon though. I've got too many projects on the go!
regards
Andy