Crosshair - 10 dbic Circularly polarized antenna tutorial!

[kev.au]

Check Readymade RC's site

-Alex

I saw that as i was putting a set of your blue beam antennas in my cart .



Thanks to Hugo and yourself for another great antenna.

[HugeOne]

I recently made a couple LHCP crosshair, I pointed a 12T RHCP helical cannon blasting 500mW right on it and hardly got any power from the oppositely polarized crosshair!
Mines would be on my site really soon, first a special 2510mhz batch along with matched 2510 windmills 2410mhz will follow.

-Great tutorial Alex! as always

-Hugo

[Tracks]

@HugeOne. ehem... Wouldn't you rather start with 1280?

[IBCrazy]

Right now Hugo and I are doing Beta versions. The Final versions will be more expensive, but they will come with a vacuum formed cover and look very professional

-Alex

[IBCrazy]

Hey guys just finish now my attempt to build the Crosshair for 5.8GHz, I must say that cost me a lot to build and finding the proper wire diameter.

Here are my measurements for CH1 on my Tx (5705MHz)

Wire diameter: 0.26mm
Height over reflector: 10.4mm
Lenght of copper tube: 13.05mm
Size of reflector pannel: 12000/5705x25.4 = 53.4mm
Short lenght: 11.08mm
Long lenght: 13.11mm

For the tube I use an old 2.4GHz rubber ducky dipole that I have on hand.

I attach some pictures of the building process.

Now I just gone crimp my connector and give it a try!!!

Great job Alex and Hugo thanks for this tutorial.

EDIT: And here it is my first quick test:


Cheers

Martin

The very first build is a 5.8GHz and the first post states that it would be too difficult. You sir, have more patience than I do

Very nice work! Let us know how the testing goes. Maybe we'll eventually do a 5.8GHz version of this antenna. I think I know of a special coaxial cable that could work really well.

So now we have 2.4, 1.3, and 5.8GHz units built. Who's going to do the first 900MHz?

-Alex

[MASHTON1138]

Almost have some 1280MHz ready to ship to RMRC!!

[Martinba77]

Thanks Alex I have on order UT141 formable coaxial now and when arrives I gone give it a second try.!
I now that the video isnt great but giveng the circunstancies of this test I think that when I cut the elements to the exact lenght and try it on open field maybe perform better. Notes that the house walls are 60cm thick, it is a very old house. Also is the snow and note that when I move apart from the yard side wall the signal get lot better. So the enviroment is the worst I can imagine to test this antenna, I just do this test to see if is just working or not. Now moving forward to do some more accurate tests.
Also I measure the amp consumition but honestly I just dont know if I must look for the lower or the higher amp consum? I get on the lower side of the band a reading of 0.19A and on the higher side of the band I get 0.21A consumition. During the next weekend Im going to measure on my detector to see the aprox. VSWR and report again.

Anyway I must wait for some better weather here and go outside and test.

Thanks for your impressive work guys!

Just a question, both ends of the tube must be isolated right? Or just the front side? Now I have both isolated with electrical tape.

Cheers

Martin

[IBCrazy]

Thanks Alex I have on order UT141 formable coaxial now and when arrives I gone give it a second try.!
I now that the video isnt great but giveng the circunstancies of this test I think that when I cut the elements to the exact lenght and try it on open field maybe perform better. Notes that the house walls are 60cm thick, it is a very old house. Also is the snow and note that when I move apart from the yard side wall the signal get lot better. So the enviroment is the worst I can imagine to test this antenna, I just do this test to see if is just working or not. Now moving forward to do some more accurate tests.
Also I measure the amp consumition but honestly I just dont know if I must look for the lower or the higher amp consum? I get on the lower side of the band a reading of 0.19A and on the higher side of the band I get 0.21A consumition. During the next weekend Im going to measure on my detector to see the aprox. VSWR and report again.

Anyway I must wait for some better weather here and go outside and test.

Thanks for your impressive work guys!

Just a question, both ends of the tube must be isolated right? Or just the front side? Now I have both isolated with electrical tape.

Cheers

Martin

Just the front side must be isolated. The back side must be grounded to the shield of the coaxial cable. The shield and the tube form a 1/4 wave section of coaxial cable. As you might know, a shorted 1/4 wave cable is a dead short and chokes rf. Therefore it chokes the common mode currents that would normally run along the shield therefore increasing axial ratio (circularity).

The bandwidth on this antenna is very wide. Like 200MHz wide. It is almost as wideband as the helical (although far more predictable). However since this uses phase shift vectoring, the axial ratrio suffers greatly as you venture off the center frequency. One thing Hugo does to mitigate this problem is that he doubles up the long element. He puts a second wire along side the long element soldered the whole way up. This helps it hold axial ratio a little better. This is how he can blast the antenna at point blank range with a high gain helical and get virtually no signal of the reverse polarization.

-Alex

[RcLab1]

Alex,
is the CrossHair ground dependent like a regular patch LP antenna?
or do I have to mount up high on a tripod?

(also, sort of out of the realm in this thread, but is the
Stacked Fan ground dependent? or mount up high on tripod?)

thanks :-)

[Sfakias]

Hello Alex!

Thank you very much for another great tutorial.

I wanted to ask you if the copper tube can be replaced with some other metallic tube, from different material and with thinner wall thickness (O.D. as recommended by you). In particular, I am thinking of using a section from an old FM antenna, roughened with sandpaper for the solder to adhere.

Thank you once again for your pioneering work.