made some RF discoveries today

[Shammyh]

What a great chart! Thanks for that! Is that something you'd be willing to share the original excel, as I would love to add some data to it.

I see you've marked ch.22 green, but I've found that is also part of the spectrum licensed by Sprint as BRS1. The entire band from 2495-2690 is licensed to various parties depending on location. The FCC calls these locations BTAs, which are basically like counties where you can operate. Currently, Sprint (who owns Clearwire) licenses about 80% of this spectrum, but the actual channels in use do vary based on the BTA.

I'd love to get some more info on use of the 2281-2401 spectrum. Yo've noted that a lot of it is for Sat/Space comm, but none of it is confirmed?

You can find the chart here: DJI P3/P4/Inspire channels

It can be downloaded from "File" -> "Download as".

I was the one who originally created it (though my work was also confirmed and improved by a few other members working on the same thing), and I did the hands-on testing for the 2.35 GHz <-> 2.5 GHz space. However... I left the document open for anyone to edit... and the community here really took the bare bones I started with and improved it massively. Just check out the revision history. In fact, I only popped on to check something the other day, and I saw all the color coding, additional information, and corrections that had been made. Collaboration for the win!

The "confirmed" column, meant I actually made the measurements using a spectrum analyzer. The rest was inferred based on the channel widths and frequencies. As far as the "usage" column, I bootstrapped that a bit from FCC docs, but other more knowledgeable folks have improved it massively.

~~~

What I'd really love to see, is creation of a new chart, perhaps on a new sheet in this same doc, for P4P bands.

If anyone wants to help in that testing (as my spectrum analyzer only goes from 2.35 to 2.5 GHz) let me know and we can get it sorted out!

I took a quick glance through the FCC docs for the P4P... and it looks like bands have been narrowed from 10 MHz for LB bands, to roughly 6 MHz.
I assume the "controller signal" is still some sort of ISM-band FHSS, but that is not confirmed.

Love to get some help on this if anyone is interested!

- Sam

 

[james_hunt]

Hi James - thanks for doing this & sharing.
Do you think the results are the same for the P3 Pro? My guess is yes it would. But not sure.

And - this is something I've always been fuzzy on - are you saying that the TRANSMIT freq. is pretty much constant in the middle of the 2.4~2.5 spectrum and the 32 channel hack only affect the Video downlink?
And does this affect the video data received AND written to the card - or only what we see on screen?

You would have the same results for the P3P. The transmit from the RC is frequency hopping over the entire 2.4-2.5 band. The 32ch hack only affects the video streamed to the remote, not the video recorded on the SD.

 

[james_hunt]

You can find the chart here: DJI P3/P4/Inspire channels

It can be downloaded from "File" -> "Download as".

~~~

What I'd really love to see, is creation of a new chart, perhaps on a new sheet in this same doc, for P4P bands.

Ha! I was just reading your original post while you were posting this... Sorry, late to the game. I would definitely love to help measure the P4P. My analyzer works to 6Ghz. But I only own the P4...

If anyone who owns a P4P in the LA area is up for a meetup and rf test??

 

[Shammyh]

Ha! I was just reading your original post while you were posting this... Sorry, late to the game. I would definitely love to help measure the P4P. My analyzer works to 6Ghz. But I only own the P4...

If anyone who owns a P4P in the LA area is up for a meetup and rf test??

That'd be awesome if you can get your hands on a P4P. Unfortunately, I'm in the Boston area, so no help there.

I can do another test on the 2.4 GHz space, since I believe the P4P has what's unofficially referred to as "LightBridge v2.5" and it may differ a bit from the P4.

What are you using for a spectrum analyzer btw? Is that a HackRF? I assume it must be some type of SDR to get that much frequency range.
I quite like my RF Explorer, but it's getting a bit long in the tooth, and I wouldn't mind splurging on a nice SDR at some point.

 

[james_hunt]

What are you using for a spectrum analyzer btw? Is that a HackRF? I assume it must be some type of SDR to get that much frequency range.
I quite like my RF Explorer, but it's getting a bit long in the tooth, and I wouldn't mind splurging on a nice SDR at some point.

BB60C • Real-time Spectrum Analyzer (RTSA) | Signal Hound

 

[Shammyh]

BB60C • Real-time Spectrum Analyzer (RTSA) | Signal Hound

Woof. Bit out of my price range.

 

[jephoto]

You would have the same results for the P3P. The transmit from the RC is frequency hopping over the entire 2.4-2.5 band. The 32ch hack only affects the video streamed to the remote, not the video recorded on the SD.

Right! Duh! Data written to sd card not part of this equation....
Thanks.

When a buddy of mine & I first started flying P3P's we found out that if we were both flying and too close to each other - both on auto channel - often our video picture on our iPad Mini's would break up & have lots of interference.
Not realizing the video stream and the control transmission were separate we were worried that one of us would loose control of the phantoms if we stayed on the same channels.
So we began to make sure that one of us went on Manual and chose a different channel than the other.
But glad to know it wouldn't have affected control of the birds.
Really glad to know about going to ch. 20 or above for non interference of our own controller though. That's really valuable info.

 

[BobbyDo]

Thanks a lot for so useful and interesting video instruction! It is very useful for me!

 

[sdavisnz]

hey man, I've got the antenna mod so I can use custom antenna, do you think its okay to use some antennas off a fairly new wifi router instead of the bundled antenna?

 

[Sprtbkryder]

They will work just fine.

 

[james_hunt]

do you think its okay to use some antennas off a fairly new wifi router instead of the bundled antenna?

I will be posting another video soon with some different antennas I've tested. Not to spoil it, but some wifi antennas do work better on certain channels than others. You will have to test it and see how yours perform. Also be sure to check that they don't have a pin inside or they won't fit your modded connectors.

 

[N017RW]

This will be true of any antenna and populations of identical models. Manufacturing variations will result in this. Ideally you'd want peak resonance at mid-band and taper to the ends

 

[Sprtbkryder]

This will be true of any antenna and populations of identical models. Manufacturing variations will result in this. Ideally you'd want peak resonance at mid-band and taper to the ends

And that's the way most are built. At least mine are I hate tuners for antennas.

 

[Perspectiveaerial]

Hey guys will the channel hack work with the new DJI 4 app

 

[chazzm]

You've got the first part right. Using the stock app, Ch.20 is the only channel that doesn't overlap the rc control data. Using the hack opens Ch. 1-12, and 21-32, none of which overlap with the rc. I've heard that Litchi has eliminated the 32 ch. version of their app...

The term "Dual Band" (in our world) refers to antennas that operate on both 2.4GHz and 5.8Ghz. The Phantom just uses the 2.4Ghz band. The stock antennas are not dual band, as they don't need to be.

Your idea of a simulated long range test has some merit for sure. I may try that next. Also I want to hook up the sunhans amps to the analyzer and directly measure what they're doing. I've ordered some adapters to do that as the RP-SMA connectors don't connect to my analyzer.

How does or would this work with the Phantom 4 Pro? Which uses both 2.4 and 5.8 Ghz? The Phantom 4 I understand because I use it on my P4

 

[Sprtbkryder]

Hey guys will the channel hack work with the new DJI 4 app

YES

 

[Perspectiveaerial]

Cool thanks

 

[Roadstar1700]

Hi people,

Being fairly new here, I thought it was time to contribute something helpful. I happen to have an RF spectrum analyzer that I use for my day job, so I thought I would put it to good use and answer some questions I had about the P4. I made a little video to provide some explaination of the RF transmission scheme on the P4, and some surprises I found. If you're confused when people start talking about channels and downlinks, hopefully this will help.

I'll try to answer any questions you have about this video in the thread below. And kudos if you find the 2 lies I told. oops.

Great video and information James. I have a question I've been trying to get an answer for. Is the AC flight data eg distance, velocity and altitude in the same stream as the video signal? If so, the green/red status light on the RC must be part of the video transmission stream.

Am I right to say that if you lose the video link and the status light goes red you may still have full control of the AC. An RTH would only occur if the AC no longer saw the RC uplink signal.

 

[james_hunt]

How does or would this work with the Phantom 4 Pro? Which uses both 2.4 and 5.8 Ghz? The Phantom 4 I understand because I use it on my P4

I believe the P4P uses 2.4 GHz for the control just like the P4, but sends the video stream on 5.8. This is much better as each has the entire band to itself, barring outside interference. If I can get some hands on time with a P4P I will be able to provide some more detail.

 

[james_hunt]

Am I right to say that if you lose the video link and the status light goes red you may still have full control of the AC. An RTH would only occur if the AC no longer saw the RC uplink signal.

That's correct for the time being. The video downlink can be completely black while you retain control. The telemetry is sent back with the video, so you would be quite literally flying blind with no instruments. It is possible for dji to program the RC to send its red/green light status to the AC with the control data so the AC would be able to RTH on video loss. But that is not implemented yet.