RC Model Reviews

More and more reading goes on about FPV...

In my travels today I found IBCrazy's Cloverleaf circularly polarized antenna! After reading a bit about different antenna types, this seems to be an awesome development for FPV. I thought I'd better share.

For those who don't want to click, circularly polarized antennas work great at any angle so your signal will remain strong even during turns and aerobatics. The cloverleaf style is omnidirectional so it replaces the default whip style antenna. It can be matched with a helix antenna, which is the circular version of a yagi, or directional, antenna. There's a great video demonstrating the effects (or lack there of) in the link, so go click it now.

rogueqd wrote:More and more reading goes on about FPV... and aerobatics.

FPV aerobatics, that sounds stomach wrenching.

The cloverleaf style is omnidirectional

no, by definition omnidirectional is spherical

Circular polarization is a compromise, by definition a compromise would not be optimax range

"I write this tutorial in the name of my Lord and Savior, Jesus Christ. It is with His heart that I write this as a free gift to the FPV community. Please enjoy."
"Engineer for Christ"

What does THAT have to do with mathematics?

ergocentric wrote:no, by definition omnidirectional is spherical

actually no
omnidirectional means that you have constant gain in one cutting plane (usually azimuth cut)
youre confusing it with isotropic

I haven't tried the Cloverleaf yet, but once my gear gets here I'll do some tests

Shotglass wrote:

ergocentric wrote:no, by definition omnidirectional is spherical

actually no
omnidirectional means that you have constant gain in one cutting plane (usually azimuth cut)
youre confusing it with isotropic

OOPS, yes you are correct, but 'cloverleaf' is not omnidirectional

Antenna theory class was over two decades ago.

well the horizontal cut has a little over a 1db variation in it which is what id call omnidirectional

Don't forget the cloverleaf is also a circular polarized antenna (separate and distinct from omnidirectional).... It's largest benefit is that it has reduced signal loss when the transmitting antenna changes polarization. The transmitting antenna on the aircraft is usually polarized in one direction but when you make sharp turn or go into a loop or some such maneuver, the TX antenna orientation changes to the other direction or something in between (this all depends on how you mounted the antenna of course, but in the end it's going to vary, no matter which way it's installed)... If you use linear polarized antennas at both ends of the transmission path, you can have a 6db drop in signal strength.... by going with a circular polarized receiving antenna, you can reduce the drop to 3db. This is why such an antenna can reduce dropout. (Forgive me on the db details... it's been so long, I may have my numbers bungled, but the drop changes dramatically with polarization changes)

I could get even more carried away as circular polarization can rotate 2 ways... left hand and right hand... much to the dismay of Amateur radio operators doing satellite communications... as sometimes the signal from a low earth orbit, spin stabilized satellite can change polarization. Hams found 2 ways to deal with the problem, either switch polarization of the receiving antenna using relays and 2 sets of wiring harnesses OR as one ham I know successfully demonstrated... go big! An array of 4 linearly polarized, high gain beam antennas could overcome the signal loss by boosting the signal so much that the db drop didn't matter.... It worked great but it's not very practical for portable use!

Anyone interested in learning more about the "Cloverleaf" should probably search for quadrifilar helix antennas as, if my rusty memory still works, is the more common name for this type of antenna.


Regards

Kaptain "Dang... I forgot what I was going to say again" Zero

after reading more thoroughly it seems the problems are multipath interference and extreme changes in signal strength, this antenna provides the the least change in intensity, and a really good SWR; it seems to be designed for the aircraft, so as long as you have enough signal strength/transmit power this looks ideal for a moving target

Gain is only 1.2dbi, making it perfect for an aerial antenna.

(an aerial aerial? hehe)

edit: I don't remember wheel antennas in my antenna/transmission line course, but they have been around for balloons since the 1950's

edit on an edit: planar wheel antenna works well with reflector and/or stacked

It's a 26 dB loss if the polorisations are mis matched. ie one aerial verticle and one aerial horizontal. You may find these threads of interest:

http://www.rcgroups.com/forums/showthread.php?t=1352583

http://www.rcgroups.com/forums/showthread.php?t=1389925

http://www.rcgroups.com/forums/showthread.php?t=1147430

HTH