Crosshair - 10 dbic Circularly polarized antenna tutorial!

[HugeOne]

Just built a 1280MHz crosshair this weekend, used brass tubing, 18ga solid core wire, RG-213, and a 30cm x 30cm piece of single-sided PCB as the reflector. Results are better than I expected:



Here's some pictures + feedpoint detail:

Nice work!

You see the two valeys in you SWR plot, circularity happen in between the two, look like you are right on.

Hugo

[airtruksrus]

Just finished up with mine for 1280 and performed a short range test (2,000 ft) with better results on the 300Mw Vtx w/spw than with the linear antennas( stock tuned whip and 8Dbi patch). Got the feeling that this configuration should be able to maximize the range but doing this with out any swr testing can throw some questions into how much better it could possibly do. Wanted to maximize the range on the 300Mw Vtx before throwing on the 800Mw Vtx.

Constructed it from 12" x12" galvanized sheet, 1/4" copper tube balun, rg-316 coax, .030 mig wire, hollow fiberglass pushrod tubes for supports and corning 1" foam board for the plate support. It's getting configured for use with the Ez antenna tracker for testing this week.

[HydroThief]

Does the piece of copper pipe that sticks out the back need to be there or can it be cut flush with the reflector?

[MASHTON1138]

Does the piece of copper pipe that sticks out the back need to be there or can it be cut flush with the reflector?

It has to be there. It is part of the overall length of the Balun which is actually longer than the height of the elements over the reflector.

[francoishaha]

Hi Alex, it's a bit off topics but i want to thanks you for all the great work you do and all the detail you give over the net. I just try my first helical today and it's amazing how well it perform! Be shure i will make this new crosshair antenna soon

the hobby would't be the same without your brain

[fpvnoob]

Amazing work guys!!

[Squidman]

Does anyone use the standard biquad antenna? I was interested in building one, and wondering if there is a build log for that as well?

[IBCrazy]

The BiQuad and many other antennas can be found here: http://www.rcgroups.com/forums/member.php?u=103113

Take your pick. There are 10 or so tutorials.

-Alex

[Maineiack]

did a walk this morning,Humid, Damp out,

put the TX 600Mw from RMRC in the window in front of a small fan

carried the RX uno from RMRC and crosshair/with 2x2 backplate, using "Base" goggles.

70deg off to the side as i walked out the door and around our drive.
perfect vid

walked out 200ft in front of CL with the crosshair pointing away from CL. my body blocking
good vid a few lines but had pic (this surprised me)

400ft, crosshair pointing to CL, small hill at 50ft infront of TX,
a line of pine trees at 300 blocking, perfect vid
turning crosshair 20 deg away from CL vid was getting jiggly

need to go out to where i grew up(out of the city) for some good distance tests

I fly a Quad, havnt flown FPV yet
and im not going for a 5-10 long range mile stretch

ill be tickled with 1/2 to 1 mile for where ill be flying

cool
Thanks for the Build thread Alex

[adamchicago]

Alex, or anyone else with a similar setup...would there be any interference or deficit in range or quality of reception if you mounted the following on the back of a crosshair antenna?

- Cloverleaf antenna (off top of antenna)
- 2x Lawmates 1280mhz VRx's (w/built-in filters)
- 2x EagleEye diversity stations (2nd div-station for future placement of 2nd Crosshair attached by hinges)
- Castle Pro BEC (powers entire station via 12V Pb battery)(this could easily be place on battery-end rather than antenna if necessary)
- cheap Chinese DVR (no screen)
- Sony two-way video switch (switch back and forth from OSD to DVR screen)