ASATopGun said:
I am looking into extending the range on my Phantom 2 Vision Plus via FPVLR products but I am a complete noob to the antenna subject and dont quite understand what I am looking at. Can someone please explain to me what I need to look for and which company you would recommend I go with?
Hi,
gain is only an aspect of antennas and you cannot estimate range just by looking at gain figures.
You have to consider polarization, some antennas are Linear Polarized, some others are Circular Polarized.
With 5.8ghz you need circular polarized antennas because of the short wavelength (about 52mm) , this causes the waves to be subject to multipath, where signal bounces off of objects, especially metal and carbon fiber, so takes a different path as opposed to just direct LOS. If linear polarization is used with such a high frequency (very small wavelength) on an analog video transmission you will see a lot of ghosting on your monitor, because video signal will come back at different times since multiple bounced signals will come back to the monitor's antennas at slightly different times.
With Circular polarization you can have RIght hand signals and Left hand signals, one is called RHCP the other is called LHCP,
if you use a TRUE RHCP antenna on the video transmitter, then all bounced signals will be LHCP (bouncing a circular polarized signal will work like a mirror, inverting its polarization direction). This is a good thing, since the RHCP antennas on the monitor will in a way reject LHCP signals since there is theoretically a -27 db attenuation between RHCP and LHCP, this allows only 1 good signal to reach the monitor's antennas for flicker free operation.
Now onto why i sa TRUE RHCP,
many junk chinese antennas are marketed as being RHCP or LHCP but in fact they are not, they use the wrong geometry and the wrong thickness of materials so efficiencies are very low and any trace of circular polarization disappears. I have seen this on the white cheap DJI antennas and virtually all chinese antennas.
The only way to obtain the needed precision is with skillfull hand crafting and individual testing and tuning. This drives the price up, especially since these good antenans are made in western countries by experienced technicians earning a decent wage, and that companies actually pay taxes to their government. Quality can be outstanding for some brands.
Mostly you get what you pay for.
Tony.
