P4 Antenna Signal, Range Questions

[Aquadrone]

I have a Phantom 4. Wonderful device. I'm trying to learn about the signals to and from each antenna. I've heard that one is for video and one is to control the drone. I've also heard that one transmits while one receives. Which one is true?

Also, the manual says the remote controller operates from 2.400 GHz to 2.483 GHz. Is this the same for the video feed? It doesn't say what frequency the video feed uses. I assume the video is a one way signal.

My questions stem from this concern. When I'm flying I often have issues with my video feed. I get a black screen for a few seconds. This is more common in populated areas, not such a problem away from civilization. But when I lose the video feed my heart beats faster as I feel like I'm also losing control of the craft, although it seems to still do what I tell it to do (if it's within sight).

So, what's really going on here? Flying blind is scary, but have I also lost the ability to control the drone? Does the controller have far greater range than the video, or is it failing on me just like the video feed is?

I also use windsurfers and they have helped, but not eliminated the problem.

Thanks for any education you can give me here.

 

[Mark The Droner]

I'll tell you what little I think I know...

The P4 uses lightbridge which is a DJI proprietary system. There's no hard document released by DJI explaining in detail how this particular lightbridge for P4 system works, but if you search around you can find a few details on how the original lightbridge worked and also how the most advanced lightbridge system works (called Lightbridge 2) and you can then put that knowledge together and make assumptions regarding the lightbridge on the P4. You're correct in that one antenna sends out the control signal and the other is for FPV.

This link might help: DJI Lightbridge 2 – Professional Quality Live Streaming From the Sky

 

[N017RW]

You can also search the FCC website based on the FCC-ID affixed to your controller.

This will not reveal protocols or other signal 'contents' but rather the antenna and emissions info.

 

[Aquadrone]

Thanks. I have given this more thought and what's more important to me at this time is what signals go in which direction; how it all works.

I assume the controller sends flight instructions to the drone and camera at some frequency.
I assume the camera/drone sends a live video feed to the controller at a different frequency, or maybe the same but on a different channel.
Mark stated that one antenna handles each task. Makes sense to me.
Question - Is the signal from the controller to the drone stronger or more reliable than the video signal coming back to the drone? In other words, if I'm having a black screen, is the drone still receiving my flight controls? Can I keep flying further away? It would seem that video is a lot of data and harder to transmit, while control signals may be way smaller (like sending a text vs. calling on your cell phone).

How does flight information, like altitude, position, speed, etc. get onto my iPad screen. Is that coming from satellite or GPS somehow? Or is that coming from the drone through one of my antennas?

What signal is coming through the cable that connects my iPad to the controller? Video?

Is my iPad picking up anything from GPS other than its own location?

It would be cool to see some sort of schematic that shows what data is flowing in which direction.

To me the frequencies don't matter, I'm just trying to understand what does what.

Thanks again.

 

[Mark The Droner]

Again, I'll tell you what little I know and I'm sure somebody will be happy to correct me...

Yes, the P4 lightbridge system uses a frequency within the 2.4 ghz range. I believe there are two frequencies used - one for the control signal and one for the FPV signal.

My understanding is the control signal and the FPV signal have roughly the same range regarding distance. But still - the FPV is likely to show issues before the control signal because the data is so complex. And maybe also because your controller, while standing in a suburban home setting, is more likely to be inundated with wifi signals from your house and your neighbors which are using the same frequency band - while your AC is all alone up there in the sky with your controller shooting a signal straight at it. I'm not aware of pilots being able to fly further out after a loss or freeze of the FPV. My understanding is it all works together as a system which is stated in the Lightbridge 2 page even if we aren't sure how that relates to the P4 lightbridge. So you may be able to fly a bit further away, but not much further, I believe.

My understanding is the telemetery data is passed along what is normally used as an audio channel within the video signal. That may be the main reason our videos don't include audio.

Eventually you will learn to have faith in the RTH system and then you won't be quite so scared when you lose the FPV connection. The RTH system will take care of everything. It is rock solid. Your AC will fly back within range all on its own, provided you have set it correctly and provided that you know how to use the RTH system. That's important. There have been cases where the pilot just stands there after losing FPV and waits for his AC to return, not realizing he still has a control connection and so the AC just hovers there several miles out until the battery becomes critical. Not good. Learn to use RTH. Learn to confidently invoke RTH. Learn to cancel RTH.

My understanding is the signal that comes through the cable is an FPV video signal.

Your flight app will use the iPad's own GPS to determine its own location and that is displayed on your map.

There is an image on the lightbridge 2 page showing how the signals with lightbridge 2 move between the AC and controller. So that might be a clue.

It's a very complex system. Even when you think you're beginning to understand the complexity of it, you'll later learn its even more complex than you thought.

 

[N017RW]

The main reason there is no audio is... there is no audio to record/transmit other than the sound of motor-whine and rushing air.
Folks who have used GoPros in the earlier models, and myself, who've strapped other cameras to their P1-2s and CP-helis can attest to that.

Having said that on-board audio could be useful in debug or fault investigations but the data logging available now can supplant what could be heard (motor operation, etc).

 

[rparge]

This is an interesting thread:

made some RF discoveries today

 

[msinger]

Is the signal from the controller to the drone stronger or more reliable than the video signal coming back to the drone?

The downlink never seems to be as strong as the remote controller signal. There's really no way to tell which one is going to drop first ahead of time though.

In other words, if I'm having a black screen, is the drone still receiving my flight controls?

It might be. The status light on the front of the remote controller will be solid green while the remote controller is connected to the Phantom.

Here are the other possible remote controller status light colors from the P4P manual:

Can I keep flying further away?

You can continue to fly until the remote controller disconnects from the Phantom. At that point, you'll be at the mercy of the automated features to get your Phantom back to the home point (or back in range so your remote controller and reconnect). They aren't perfect, but they do work well in most cases when no obstacles are in between the Phantom and the home point.

How does flight information, like altitude, position, speed, etc. get onto my iPad screen. Is that coming from satellite or GPS somehow? Or is that coming from the drone through one of my antennas?

The Phantom's current location comes from the Phantom's internal GPS receiver. All other data is calculated by the Phantom. That data comes down to the remote controller via the downlink and is transferred to DJI GO if it's running and connected to the remote controller via a mobile device.

Is my iPad picking up anything from GPS other than its own location?

No.

 

[AirMan05446]

Good thread. I've found I can get usually get longer range video by lowering the video transmission rate settings. This lowers the quality, but helps keep the video stream stable for a longer range. Flying higher will usually get you some more range as well.

There are other factors that affect range, like signal congestion and other types of interference -- and that has more to do with where you fly from and when.

My ideal flying scenario for range:
- a remote hill with a nice, panorama view of the sky. I call this "Big Sky Country". (not easy to find in Florida, BTW!).
- Early morning, 1-2 hours pre-dawn: Nice & cool, WI-FI interference is lower, air traffic is at a minimum, can keep VLOS with strobes.
- McDonald's in my tummy. (for some reason I always can get better range after a meal at McDonald's.) Another DJI plot? Probably.

Any way, have fun and always be scouting new locations. It keeps things fresh; just make sure you check the area for hazards (and McDonald's).

 

[Mark The Droner]

...
- McDonald's in my tummy. (for some reason I always can get better range after a meal at McDonald's.) Another DJI plot? Probably.

Any way, have fun and always be scouting new locations. It keeps things fresh; just make sure you check the area for hazards (and McDonald's).

 

[Techcop50]

You might want to try a simple Windsurfer antenna parabolic. Just remember to keep it pointed in the direction of the drone.
https://smile.amazon.com/Parabolic-...TF8&qid=1508510252&sr=8-3&keywords=windsurfer

 

[Aquadrone]

You might want to try a simple Windsurfer antenna parabolic. Just remember to keep it pointed in the direction of the drone.
https://smile.amazon.com/Parabolic-...TF8&qid=1508510252&sr=8-3&keywords=windsurfer

I do have those already, the exact ones I believe. They help some. Thanks.

 

[AirMan05446]

Love it! Wonder if they'll serve my Phantom at the drive thru.

 

[Aquadrone]

Good thread. I've found I can get usually get longer range video by lowering the video transmission rate settings. This lowers the quality, but helps keep the video stream stable for a longer range. Flying higher will usually get you some more range as well.

There are other factors that affect range, like signal congestion and other types of interference -- and that has more to do with where you fly from and when.

My ideal flying scenario for range:
- a remote hill with a nice, panorama view of the sky. I call this "Big Sky Country". (not easy to find in Florida, BTW!).
- Early morning, 1-2 hours pre-dawn: Nice & cool, WI-FI interference is lower, air traffic is at a minimum, can keep VLOS with strobes.
- McDonald's in my tummy. (for some reason I always can get better range after a meal at McDonald's.) Another DJI plot? Probably.

Any way, have fun and always be scouting new locations. It keeps things fresh; just make sure you check the area for hazards (and McDonald's).

Interesting, how do you lower the video transmission rate?

 

[tevek]

Interesting, how do you lower the video transmission rate?

Power everything up, go into the camera view of the app.
Tap the three dots top right hand corner.
Scroll down to HD settings and tap that.
Scroll down and you should see the slider to adjust your image transmission bit rate.
I usually trim it down to 4mbps and select a custom channel that is free of interference.
You need to be powered up to see and save these settings.

 

[Mark The Droner]

Decreasing FPS could help too...

 

[Aquadrone]

Decreasing FPS could help too...

Is that Frames Per Second? Will that impact the quality of the video being captured on the drone, or just the feed to the controller?

 

[Mark The Droner]

The latter provided you're in the right menu