How to build a 5.8GHz Helical Antenna

[Craftydan]

it will just be attenuated / the signal will be weaker.

And by "weaker" he means it'll work on the bench or at your feet, but not at all when you get any distance.

The attenuation from polarity mismatch is VERY severe. The low range attenuation you feel at short range is deceptive -- it follows a square-law effect.

On the positive side, you can stand next to a big metal building and the reflected signals will come in clear . . . sorta . . . except they're probably scrambled and attenuated a bit in the bounce . . . pretty much what you want to filter out using the polarity


As for your helical antenna . . . spin the coil the other way and it's reversed. If you build your support structure in two flat pieces (like cross-hairs), flip one and it's reversed the thread. Then reversing the polarity is a matter of flipping your template, bending some more wire and de/resoldering the feed line.

 

[FraserJ86]

Does the reflector board have to be fiberglass board copper? Cant you just use a really cheap zinc sheet or some other non copper sheet? I have loads of kydex, so was thinking of backing a sheet of something with kydex.
Was also thinking of using some coax cable with SMA solder plug instead of the one shown in parts list. I guess im looking to build something similar to the VAS versions of the helical.

 

[Craftydan]

The "reflector" is effectively the antenna's ground plane. So long as it can hold an EM Field and has very low impedance to the coax shield (good conductor with a good solder joint) it should fit the bill.

 

[funaro13]

muito bom parabens ao autor !!!!

 

[Paul0]

Build a helical last night

Views and comments welcome

 

[rockyboy]

Looks great! Have you had a chance to test it out, either on the bench or in the field?

 

[Paul0]

Hi!

Just on bench. Left camera and tx with dipole antenna on. Went to other size of house upstairs and still solid picture. Sadly its not a internal brick house so i think it wouldnt have much problem breaking the walls.

Need to do a field walk test i think. Im a bit nervous to do a flight incase i loose vid as i built this because i had issues with rx antenna i was running.

Is a steel reflector good enough? Also the helical is 1.6mm which is prob a bit to thick maybe.

Overall im more than happy how it went together in the end

Paul

 

[rockyboy]

Very cool! I have zero experience with this type of radio signal work, but I'm very interested in learning

 

[Craftydan]

Steel reflector should be fine. The ground plane/reflector needs to interact with the electromagnetic wave being built in the coil, so as long as it's a good conductor and interacts magnetically it's well suited for the task.

Curious, though . . . You have a small support about 1/4 turn in. That's a non-conductive material, right? Hard to tell from the pic. The antenna would likey still "work" if it was conductive (test for function in your house would be fine) but it wouldn't​ perform anywhere near as well as a 5 turn helical should.

BTW, welcome to the forum!

 

[Paul0]

Hi

Thanks for the welcome

The bit you are talking about is conductive and its the wave trap. But looking and thinking about it. I might be a bit far up? And iv also seen people say that there not needed on 10awg wire.

The wire on my helical is 1.6mm would i really need a wave trap?

Thanks
Paul