Thread: Mini-HowTo Build your own TX antenna for FPV View Single Post
Dec 16, 2009, 10:10 PM
Engineer for Christ
Amherst, VA
Joined Jun 2006
11,093 Posts
The inverted Vee

Inverted Vee

I have been getting raves about this antenna on people's airplanes and many success stories. It is my highest recommendation that you try it.

This is perhaps the best general purpose antenna. Suitable for medium range and altitude, this antenna has lower isotropic gain (2.15-1.5) however has a very uniform radiation pattern. It allows for best signal when doing stunts such as loops and rolls without loss of signal. Polarization is also less of a problem. Higher gains are achieved at higher angles (closer to flat like the dipole). Lower angles up to 90 degrees increase the radiation patterns resemblance to a sphere. I’m going with 120 degrees as it has the best characteristics for my purposes.

Construction:

This is simply the dipole antenna with a lesser bend in it. There is however a degradation factor for the angle. Refer to the above construction of the dipole, then use the below values to trim your antennas to the proper lengths. See the diagram for how to feed this. I no longer use a direct feed, but an offset feed. You can see this on the tail of my P-38 airplane in the pictures. Note how the coaxial cable comes out at an angle.

So the antenna quarter wave lengths are calculated as:

Quarter length * degradation = Proper antenna length.

For 180-165 degrees – 0%
150-165 – 98%
120-150 – 97%
105-120 – 96%
90-105 – 95%
You can also use this calculator: http://www.cdxa.org/antenna_cal_diople.html

Empirically, the proper element length (already compensating for the degradation factor) comes out to: Length in inches = 2715/f in MHz - or - Length in mm = 69200/f in MHz

Note that the elements are separate. One is connected to the driven pin, the other is connected to ground. This is the same antenna as the Dipole but just bent at an angle.

Mounting:

Mount this with the open side of the Vee facing the nose of the airplane when flying distance as this will give a stronger signal for the return trip. Mount it with the Vee facing sideways for stunt flying As this will help keep the antenna in polarization better.

Performance video
This is a video of my Vee antenna with an 8dbi patch on the ground. 2 miles with plenty of strength! This is why you build a homebrew antenna!

 2 Mile Record FPV Flight (3 min 10 sec)