Ok, I can't believe I just stumbled upon this thread.
Anyway, the parabolic reflector isn't such a bad idea, but I don't think the dish is tune to the 2.4 Ghz band.
123River1,
Here's an image of how parabolic reflector works:
File:Parabola with focus and arbitrary line.svg - Wikipedia, the free encyclopedia
It concentrates the signal it can gather over a larger area into a single point. And it re-broadcast the signals all out in same direction. I mean you would have to hold your controller pretty steady. I mean REAL steady.
So you would need to place your antenna near or around where "F" is, not behind the dish. Another issue is that you would need to be able to move the dish as your drone moves. Now, assuming you are only going 1 direction, you can potentially aim the dish in that direction. However, this becomes difficult as you are moving in all three X, Y, and Z plain.
I've tried the ITE Mod on my P2V+ and it works GREAT! I was able to extend my range out to about 8000+feet.
If you want to go for the "LONG RANGE", I think you will want to ditch the P3 Standard and go for P3 Advanced or P3 Professional. I recently (black Friday) bought a P3 Professional, flown it a dozen time. It can go about 8000 feet from point of origin w/o even trying. That's because while P3 Standard uses analog signal, P3 Advanced and P3 Professional uses digital signal couple with FFT (fast Fourier transfer) that enables the drone to pick out a signal from all the noises. In fact, you can pick out a signal that's much weaker then background noise That is how P3 Professional and P3 Advance able to go such a far distance.
Now with its superior signal processing capability, all you need to do is boost the signal a little bit (perhaps with an amplifier?) and you can pretty much go out of the range of what your battery is capable (assuming the return trip is important too).
A Note on the ITE mod. Simple physics is that you don't get something for nothing. The "mod" simply focuses all the transmission in a general direction. It takes the signal that's broadcasting somewhere else toward where you need it. This is great if you know where your drone is and you point in that direction. In concept it's great, in practice, when your drone is "out there" and out of sight, it is a little bit difficult to "aim right". People do get good at "aiming" at "nothing" after a while. This is generally called "directional antenna".
I see that you've already bought the P3 Standard ITE Kit (hope you got the right one: ITE-DBS01_V.1), so perhaps you can take this time to look over the instructions on how to install it and use it.
Phantom 3 Standard solution | DBS Mods
In a nutshell, you are basically replacing the antenna. So open the case and see where your original antenna goes, and that's where you want to replace with the ITE-DBS01 antenna. Here's a slight twist: The whole antenna setup from "DJI" are internalized. That means you have no access to any of it until you open up the controller. The "ITE-DBS01" mod, brings the antenna connection to OUTSIDE of the controller. This allows you to hook up any other antenna you choose. The "connectors" for antennas are fairly standard if not a bit confusing. So inside the controller, you are essentially installing an "extension cord" to bring the antenna connector to outside of the controller. Then outside of the controller is where you connect your antenna going forward.
So while this video below is for "Phantom Vision 2 +", I think watching this a few times would help. The exact specifics are different, but the general concepts are the same. Post #110 from "GaDrone", first pictures will show you the three connection points that you want to install the "extension cord" to bring it outside of the controller. This is exactly the same thing that's done for Phantom Vision 2+, so looking at the video below will help you understand: