Offset Dish antenna

skyscraper · April 07, 2014, 02:01:55 PM

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.

Attached is the OpenSCAD source if you are interested in having a go at it!

regards
Andy

skyscraper · April 08, 2014, 11:35:40 AM

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.

EDIT: And as Rob Thompson pointed out, you need a helical of opposite polarisation to the one on your aircraft!

regards
Andy

FPVSteve · April 08, 2014, 11:55:01 AM

This is pretty interesting, let us know how you get on. One of these would look cool on the side of a van :D

rob.thomson · April 08, 2014, 12:53:08 PM

I imagine just a simple LHCP clover would suffice. The gain comes from the dish

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skyscraper · April 09, 2014, 10:23:52 AM

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 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 :)

regrads
Andy

rob.thomson · April 09, 2014, 10:51:20 AM

Could I suggest a £10 TBS patch type antenna?

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skyscraper · April 09, 2014, 10:58:28 AM

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

rob.thomson · April 09, 2014, 11:15:49 AM

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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skyscraper · April 09, 2014, 11:26:45 AM

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