Dji lightbridge video downlink12/17/2023 Yes, it would be interesting to see if they took each other into account when deciding how to set up the TDM. ![]() The Phantom relies on being synchronized to your controllers hop sequence in order to overcome all the noise at 2.4 ISM. If you had an environment where most ALL the 2.4 ISM band was occupied by WiFi, etc., not being able to escape the ISM band would indeed effect how well you could see the video downlink as distance away from the video downlink transmitter increased.Īlso remember from the control uplink perspective side of things, just because the 2.4 ISM RF environment where the operator is standing is "clean" that changes dramatically for the Phantom when it flies over a plethora of 2.4 Ghz sources. Loss of the additional "channels" has NO effect on the control link side of things, it just gives you fewer clean places to put your video downlink signal. If you were in a very heavily saturated RF environment (like a room with several WiFi AP's around you, etc., ) it would likely degrade the quality of your video downlink, but overall it doesn't seem to make a huge difference in field tests where "auto" channel selection is implemented in a average suburban environment. Image 23 Depicts the video downlink operating inside with 2.4 Ghz ISM band along with the controller's frequency hopping activities. Image 22 Depicts the controller signal hopping across the 2.4 Ghz ISM band with the video downlink channel not shown. Image 16 Depicts the video signal operating just outside the 2.4 Ghz ISM spectrum with the controller occupying peaks spread across the 2.4 ISM band. Image 09 Depicts the controller operating within the 2.4 ISM band on the left (spread spectrum) and the video downlink frequency (1o Mhz wide) operating above the 2.4 ISM band in one of the "upper channels" on the Lightbridge system. Image 23 Depicts the video downlink signal (10 Mhz wide peak)within the 2.4 Ghz ISM band with the controller FHSS signal peaks on either side. I have attached some photos of the spectrum analysis of these systems. These are 10 Mhz wide channels with the center frequency being listed and 5 Mhz being occupied on either side of center.Īs you can see, many of these channels are clearly outside the 2.4 Ghz ISM band, which is why they are locked out of the application. Both uplink and downlink systems appear to be using MIMO (multi-in-multi-out) diversity antenna systems with an RF output power collectively at ~750 mw for each system.īelow is a list of frequencies the GFSK video downlink system uses corresponding the the DJI "Channel" number. ![]() One system for control of the aircraft which operates in the 2.4 Ghz ISM band (exclusively) for control uplink, using spread spectrum and another system that can operate anywhere from 2.28-2.6 Ghz which is a GFSK (Gaussian frequency-shift keying) digital video signal for downlink of the video image. ![]() The Phantom 3 Advanced and Professional seem to be using two separate RF link systems. Using a Rhode & Schwarz DDF007 receiver I was able to get a pretty good idea of how the system functions within the RF spectrum. It should be noted that the channels outside the 2.4 Ghz unlicensed ISM band have been locked out by the more recent versions of the application to prevent illegal operation outside the ISM spectrum. I have unlocked the application installed on my mobile device to be able to select all 32 Channels that Lightbridge offers. Recently, I have taken a little time to profile the RF systems for the Phantom 3 "Lightbridge" system.
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