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DJI FPV Goggles antennas

4th_Dimension

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So does anyone know which 2 antennas are responsible for TX and which 2 antennas are responsible for RX on the DJI FPV Goggles? I read somewhere but I can't remember where but they stated that the antennas TX & RX but t when which ones.

Thank you,
4th_dimension
 

HighTechPauper

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I saw someone "theorize" that 2 were for TX and 2 were for RX, but that doesn't hold water with what I know about this type of technology. In the "Full Duplex" world of RF, just like Full Duplex anywhere else, both TX and RX happen at the same time on the same antennas, which makes the most sense here also, I think you will find in the long run that the DJI system is a Quadversity scheme with 4 equal LHCP Omni directional antennas and the goggle circuitry either combines 1 or more receivers, or looks at the best quality receiver dynamically.

Just out of curiosity, why do you ask? What are you hoping to do and gain?
 

4th_Dimension

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Good evening my friend, well I am asking as I have this crazy idea. I am thinking about connecting 2 patch antennas to each antenna connection. Which would give me a total of 8 patch antennas. Each antenna has a 9.4dbi gain so each antenna connection would have 18.8dbi gain. Thats why I asked. The only problem I can see is multipathing interference. I am hoping to have much better signal reception with this setup if it can work.
What do you think?
 

HighTechPauper

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I would need to refresh myself on my RF theory to be certain, and I am all for experimentation, but from my memory this is what I think would happen.

When you connect 2 antennas to 1 receiver, you will need a T connection, this will not double the dB of gain as you suggest, in theory it would reduce the gain, and the SWR will likely be high on the TX side of the house which is never good for the transmitter itself or good for the amount of power being transmitted. In the worst scenario it could blow your TX section on that port, at best it would effect both transmit and receive in a likely negative way. I think, based on what I know, that you would be much better off by putting good LHCP patches on 2 of the RX's and a good LHCP omni on the other 2, and I have seen people running 3 patches and only 1 Omni. I also would change the quad antennas too since that would actually give you more bang for the buck than the goggle side.

To be certain would require more information about the RX design and antenna priority scheme, for instance, is it 2 diversity receivers, and if so which antennas are paired (assuming both left and both right would be the pairs, but you know what happens when we assume), or is it 4 mono receivers and the composite video is from the strongest/best signal, or is it a rebuild composite of all the best qualities from all the signals (like the Rapidfire or Fusion RX's). It could also be a single receiver and it sees the 4 antennas as a "balanced tuned antenna array" (something your T connection from your idea would not do well given it is not balanced or tuned through antenna design or added circuitry). One thing is certain, DJI is pretty fat lipped about it, oh what I wouldn't give to talk to the lead RF, RX, and software design engineers on the project.

There is a lot to consider to actually "improve" your signal instead of hurting it, or possibly even your gear. While this is not scientific, you may want to watch and look for videos like this to see what is working for people and what you can learn about its design and operation. I would also look into the VAS Cyclops or the TrueRC or other reputable RF design manufacturers setups for the goggle side, since a bunch of smart guys with access at a high level to test equipment and insider knowledge about the DJI RF design, have already designed great "upgrades" and done the real science to see what works best.


Just my humble opinion sir...
 
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HighTechPauper

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Also DJI could be doing beamforming with the 4 antennas in a phased array, like I said, I wish I knew more about the design of the RF/RX sections, good video on this phenomena here.

 
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4th_Dimension

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Thank you sir, I will dig around again about this. But I am the thining I read that the "top" 2 antennas are for TX and the bottom 2 antennas are for RX. For some reason that is stuck in my mind
 
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HighTechPauper

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You're welcome, please let us know what you find, and please add links to any concrete info or theorized info on the subject.
 

4th_Dimension

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All right gentleman, I found what I was looking for and this guy explains the DJI FPV Goggles antennas the best. The top 2 antenna "transmit as well as receive"
The bottom 2 antennas only receive"

 

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