Some questions on 5.8Ghz antennas

[Nogas]

Firstly thank you Alex for all the time you dedicate to making FPV an even more interactive experience for alot of us. I love the fact that i know nothing about RF yet can make a set of antennas that can potentially give me video 5 - 10 even 20 kms away. All from a few dollars of raw materials.

Now, to pick your brain (and please, anyone else is welcome to chime in if they know what i need)

1) What is a good 5.8Ghz vrx antenna to go alongside a SPW in a diversity set up? I wont be flying beyond 2.5km (only using FrSky RC) and would like to be able to fly amongst some obstacles / trees / etc. Wide beam angle would be a big plus too but not sure if i'm asking for too much

2) I have built a set of CL / SPW's and while they gave good results they were a bit messy and i would like to try again so have a few questions regarding fine tuning.

As i understand the length of the arms on the lobes need to be trimmed to allow for the width of the the insulator (on the lower arms) and the feed gap (on the upper angled arms) but i am not 100% sure on which point i am trying to gauge my 1/4 wavelength from.

a) Does the lower arm (horizontal) need to be 13.233mm (1/4 wavelength) from the centre of the signal wire to the centre of the wire at the bend?

b) Does the angled arm need to be cut to measure 1/4 wavelength from the centre of the lower intersection (on the same plane that the lower arms meet) or centre of the upper intersection (on the same plane that the upper / angles arms meet) (as marked in the below drawing)



3) What can i use to get the solder to stick to the copper coated mig wire. I am using .6mm wire and 60 / 40 lead tin rosin core solder. Flux kind of helped but it was still very difficult to get a good clean join.

Thanks for any advise.

[Vitamin J]

Get a helical, 5-turn would be great for that range especially behind trees. You'll have to wait for Alex for the rest

[Nogas]

OK thanks Vitamin J, so i did a quick search on a 5 turn helical and that would appear to give me only a 45 degree beamwidth.

Will a 3 or 4 turn give wider beamwidth (than the 5 turn) yet still out perform the SPW for range?

[Vitamin J]

That is the beamwidth for perfect circularity but you can go outside that with good performance still. At 1km out the beam is about 1km wide so you have a lot of room to fly in.

I think Alex flies with a 3-turn so you may like that as well.

[Nogas]

So a helical would definately be better than a patch for my application?

Are there any tutorials on building 5.8 Ghz helicals? I've looked through the first few pages of Alexs helical thread on RCGroups but its heavily focused on 1.2Ghz. I will keep reading as i am pretty sure i've found some info on 5.8's in there before. Just not so easy to find when you really want it.

[MASHTON1138]

1) What is a good 5.8Ghz vrx antenna to go alongside a SPW in a diversity set up? I wont be flying beyond 2.5km (only using FrSky RC) and would like to be able to fly amongst some obstacles / trees / etc. Wide beam angle would be a big plus too but not sure if i'm asking for too much

Alex and I fly with 3 turn 1280MHz Helicals. 5 turn will be just fine for you and really is along the lines of what you would really need at 5.8 to have reliable penetration. As VJ said the beam width will be wide enough to give a good margin of error and plenty of flying space.

2) I have built a set of CL / SPW's and while they gave good results they were a bit messy and i would like to try again so have a few questions regarding fine tuning.

As i understand the length of the arms on the lobes need to be trimmed to allow for the width of the the insulator (on the lower arms) and the feed gap (on the upper angled arms) but i am not 100% sure on which point i am trying to gauge my 1/4 wavelength from.

a) Does the lower arm (horizontal) need to be 13.233mm (1/4 wavelength) from the centre of the signal wire to the centre of the wire at the bend?

b) Does the angled arm need to be cut to measure 1/4 wavelength from the centre of the lower intersection (on the same plane that the lower arms meet) or centre of the upper intersection (on the same plane that the upper / angles arms meet) (as marked in the below drawing)

You are over analyzing this. Cut the lobes to length and make the feed gap as small as you physically can, then adjust the lobes on the active element side by the length of the insulator on the feed point just a mm or two.

3) What can i use to get the solder to stick to the copper coated mig wire. I am using .6mm wire and 60 / 40 lead tin rosin core solder. Flux kind of helped but it was still very difficult to get a good clean join.

Higher temp soldering iron and lots of practice. You need a minimum of a 40watt iron, and it should be variable temp. I personally don't use flux only rosin core solder.

Good luck

[Nogas]

Thanks for the replies Mashton. 5 turn helical is sounding like its the go.

I hadn't attached the drawing in my original post but have now.

So just to confirm, the active element (what i was calling the upper arm) needs to be shortened by the distance the insulator sits above the stripped shield. So the virtual intersection would be the lower point marked on my diagram. And, do i also need to shorten the length of the lower element (horizontal arm) by the radius of the signal wire and the insulator?

My larger irons dont have fine enough tips so i had to use my 30W adjustable temp iron. Maybe this is my problem?

[MASHTON1138]

Just leave the bottom arms alone.