Phantom 3 Channel <-> Frequency Table

[dedstik]

Thanks, great information.

Question: If you go to a RC airpark they want to know what frequency you radio is transmitting on. Any way to know this?

Marc

Hi Marc,

I fly in an area with many electric fixed wing and multirotor aircraft. Having 10 or more aircraft in the air at the same time is not at all uncommon on a weekend...Scale foamies, FPV racing quads, long range FPV stuff, gliders, you name it.

Everyone is flying some version of spread spectrum 2.4GHz radio control and there is never any mention of individual channels because it's a moot point with frequency hopping.

With regard to FPV video down link frequencies we always check with other flyers before turning on (5.8 and 1.28GHz are the most popular). All the experienced FPV flyers know that the DJI products operate on an essentially "proprietary" frequency scheme.

I have never witnessed a DJI P3 cause direct interference with more traditional FPV down links or with the modern 2.4GHz transmitters.

When I'm flying my P3 and have my HeadPlays on and someone walks by and either asks what freq. I am on or is announcing their VTx freq. (i.e "Boscam channel 7") I simply reply "DJI proprietary" and that is completely sufficient.

:harry

 

[calvin56]

OK to show my lack knowledge im having problem getting signal on the display ... I would think that if the system is close it would show some channels with more signal than others. but they are all in the dirt and cant even tell what channels are better or not. this is with the phantom3 and android running dji go.[



QUOTE="Shammyh, post: 485242, member: 23191"]Hello all!

P3_FreqBands.xlsx - Google Sheets

I made a table of observed rf readings via a RF Explorer 2.4 GHz meter and put them in a Google Sheet.

Publicly editable should anyone wish to correct a mistake or add further useful information.

Spoiler: click for BIG rendered image of the table

Few observations:

1) Video is transmitted via ~10 Mhz wide channels from 2280 MHz to 2600 MHz. (600-280)/10 = 32 channels.

2) Control surface (analog sticks, buttons, etc) is ~1-2 MHz wide, and hops in the 2400 MHz 2490 MHz range only. The user-editable "controller channel" does not affect this signal.

3) Phantom channels 13-20 (as well as the control signal hopping) overlap WiFi 802.11b/g/n 2.4 GHz channels 1-14.

I have some screenshots from the spectrum analyzer, but for another post.

Would also like to take a closer look at the control signal in the future. Is it similar to DEEST or FASST? Don't know.

Enjoy!

- Sam

Edit 1: Updated with correct center frequencies and ISM start point.[/QUOTE]

 

[fabbio]

Hi guys,
thanks for all your work here.

However I do have a question (maybe two): let's pretend for the sake of the argument not to have legal or environment-related restrictions on channel choice. (a dream! )

Technically speaking, do you think aerials mounted on P3s will be really efficient on all the spread band? Will be there any sweet resonant spots to aim for instead of "just" expanding channel choice as many of us do ?
Is there any way to "Rhode-and-schwarz" P3's aerials in order to assess their resonance profile?

Cheers
fabbio

 

[Roger 2112]

Hey Shammyh thanks for the great post and resource for the freq table, this is very useful. I made a little update for Amateur frequencies in your Excel sheet. Based on your observations a few of the freqs map to FCC allocations that ham's can operate legally on within the expanded frequencies modification (Phantom channels 3 and 12). This is absolutely fabulous and I do hope that DJI will consider this as a tremendous value going forward for legitimate amateur operators to legally access these additional frequencies and not close those channels. Obviously the other out-of-bounds frequencies aren't of any legal use for responsible pilots and it is important for everyone to understand that these are not legal operating frequencies. For those who are not amateurs wanting to access a few extra frequencies these are available to all the current license levels available today so consider getting yourself a basic "technician class" Amateur license for legal and safe expanded frequency capabilities!

Thanks,

-Roger

 

[PeterW_R]

Do we know what chanels would be legal in Europe? I asume CE regulations would apply instead of FCC.

 

[WetDog]

Hey Shammyh thanks for the great post and resource for the freq table, this is very useful. I made a little update for Amateur frequencies in your Excel sheet. Based on your observations a few of the freqs map to FCC allocations that ham's can operate legally on within the expanded frequencies modification (Phantom channels 3 and 12). This is absolutely fabulous and I do hope that DJI will consider this as a tremendous value going forward for legitimate amateur operators to legally access these additional frequencies and not close those channels. Obviously the other out-of-bounds frequencies aren't of any legal use for responsible pilots and it is important for everyone to understand that these are not legal operating frequencies. For those who are not amateurs wanting to access a few extra frequencies these are available to all the current license levels available today so consider getting yourself a basic "technician class" Amateur license for legal and safe expanded frequency capabilities!

Thanks,

-Roger

While it would be 'nice' if DJI opened the Phantom to the amateur bands, I would really doubt they would even think about. Very little gain for them and it would open them to some degree of legal liability. Amateur gear is misused throughout the world where enforcement is spotty. You would have some protections if you are licensed - and you are following the rules carefully. It is certainly possible to do this legally if you are licensed, but it is anything but trivial.

Right now, your best bet if interested is to get a Technician's class license and carefully study the literature. Just slapping on a couple of amps isn't quite what the FCC had in mind when they opened up this spectrum to amateurs.

 

[Roger 2112]

Do we know what chanels would be legal in Europe? I asume CE regulations would apply instead of FCC.

Good question, I've updated the Excel sheet to differentiate between Region 1 and Region 2. Region 1 has a vastly expanded opportunity in the 13cm band than we do in Region 2.

Roger

 

[Roger 2112]

Just slapping on a couple of amps isn't quite what the FCC had in mind when they opened up this spectrum to amateurs.

Interesting point and I suppose one worthy of clarification. Comments on using Amateur bands are limited to the scope of legal operation within licensed amateurs. While some members have commented about performing the DJI channel expansion mod for the sake of increasing range the truth is that all this mod would do is offer additional options when the user is located within a saturated environment in which the typical DJI channels are in use or experiencing undesired interference. This mod will not increase the power output of your radio transmitter. However DJI has by default limited the channel selections to legal unlicensed usage so unless the user is a licensed amateur operator there is no legal advantage of performing this mod and with the increased scrutiny of this hobby it is important for pilots to operate within legal guidelines.

For the Amateur operator this is a unique opportunity to enjoy an additional "Privilege" and escape some of the congestion pitfalls associated with the 13 cm band.

Back to the power comment, that's not what this mod is about and people should understand that. This mod will not give you increased power but it "May" give you increased range if you are able to acquire a down-link video frequency that is free of the interference associated with an alternate channel that you may have otherwise been stuck with.

Regarding amps; lol, that's just funny. Within the amateur band plan one could maximize the legal power and I think most of us already try and optimize our reception. But seriously the advantages of amplification would be in direct conflict with (What we have here in the states) the FAA's guidelines on flight within visual line of site so it's pretty much doa. Possible in theory but certainly not practical and I haven't read anyone in this thread to this point suggesting amps anyway.

In short this mod does provide limited potential for Legal Amateur Operators to navigate their video downlink frequency to hopefully a less saturated and available space, legally, which will perform better than a crowded frequency.

73's and happy flying

- Roger

 

[Shammyh]

Hey Shammyh thanks for the great post and resource for the freq table, this is very useful. I made a little update for Amateur frequencies in your Excel sheet...

Glad to have been of help!

And thanks for taking the bones of my sheet and adding all the additional information and formatting!
Very much improved!

~~~

It's an interesting situation... where the "Lightbridge" is really just a SDR attached to a Davinci video DSP, with a fairly wide RF front-end. Lots of discussion/speculation about what exact protocol is in use for the video/telemetry side, but my money is on something similar to WiMax or DVB-T.

The baseband/radio itself is probably capable of running on a very wide variety of frequencies, though I have no idea how flexible that RF front-end really is.

Out of curiosity... as I'm not a ham/amateur operator myself... but as the "Lightbridge" signal is encrypted in some way or another... does that limit the ability to use it across amateur bands?

~~~

Also... the legal situation is interesting in broader terms. I have a few friends who are into ham, and they all (as you guys do clearly as well) take the rules very seriously. Little bit more seriously than I would... TBH.

OTOH, you have tons of folks on this forum using the "channel mod" and running channels 29-30, aka, 11.5-12 cm bands, with 2 or 3 watt boosters. Not only are those boosters not tuned for these frequencies, but neither are the antennas! Plus, this is clearly illegal under FCC rules.

Personally... I do bend the rules, and often use the upper end of the 2.4 GHz ISM, around 2490 MHz. Technically not okay... but the noise floor is significantly lower once you get just above WiFi, which for me, in an urban area, makes a huge difference. I also fly a little bit beyond VLOS (and lots of auto-pilot missions for photogrammetry, where I can't always see the bird), but the FAA is currently only politely asking that pilots stay in VLOS, it's not actually the law/rule, so I happily exploit that for now.

Anyway... just curious what you RF guys think about this situation... since to my knowledge, no one has actually come after a Phantom pilot for abusing/misusing the licensed RF bands. Also... most people running outside the spec frequencies are using fairly high-gain antennas... so not sure how that factors into it either.

 

[Roger 2112]

Glad to have been of help!

Out of curiosity... as I'm not a ham/amateur operator myself... but as the "Lightbridge" signal is encrypted in some way or another... does that limit the ability to use it across amateur bands?

What a great discussion, there's several points to this and the first would lead us to 97.215 Telecommand of model craft and 97.217 Telemetry whereby control signals and telemetry signals are not considered codes or ciphers intended to obscure the meaning of communications. 97.309 basically says one can transmit an unspecified digital code as long as the digital code is not intended to obscure the meaning of the communication. Again there's an exception for telecommand and telemtry but lets take a look at another proprietary amateur technology known as D-Star by ICOM. This uses a proprietary algorithm to convert analog messages into a data bitstream which hams can not decode without the purchase of a device with the D-Star chip. Same thing with Yaesu Fusion and the Motorola MOTOTRBO (Although there are some hacks). But this sounds very similar to what DJI has done with the lightbridge in terms of prioritization and since the telemetry is coupled with the downlink video stream it seems like it passes the smell test in regards to telemetry anyway. Clearly there's some fuzzy and vague shades of gray lines and the industry as well as the FCC seem to be turning a blind eye or simply wavering on digital communications as an emphasis to minimize bandwidth while maximizing data throughput with some tolerance towards obfuscation that digital technologies introduce.

~~~

Glad to have been of help!

I also fly a little bit beyond VLOS (and lots of auto-pilot missions for photogrammetry, where I can't always see the bird), but the FAA is currently only politely asking that pilots stay in VLOS, it's not actually the law/rule, so I happily exploit that for now.

Good point on the FAA. My brain tends to overlap between the FAA and the AMA guidelines where AMA states "VLOS is to be maintained", but that's not intended to create a debate regarding the relevancy (or lack of) the AMA. One of the greatest features of the DJI lineup is the ability to fly outside of the AMA sanctioned fields and yeah it's possible that VLOS may "Accidentally" be surpassed from time to time

 

[Roger 2112]

DJI Phantom 3 pro encryption:

What a great discussion, there's several points to this and the first would lead us to 97.215 Telecommand of model craft and 97.217 Telemetry whereby control signals and telemetry signals are not considered codes or ciphers intended to obscure the meaning of communications. 97.309 basically says one can transmit an unspecified digital code as long as the digital code is not intended to obscure the meaning of the communication. Again there's an exception for telecommand and telemtry but lets take a look at another proprietary amateur technology known as D-Star by ICOM. This uses a proprietary algorithm to convert analog messages into a data bitstream which hams can not decode without the purchase of a device with the D-Star chip. Same thing with Yaesu Fusion and the Motorola MOTOTRBO (Although there are some hacks). But this sounds very similar to what DJI has done with the lightbridge in terms of prioritization and since the telemetry is coupled with the downlink video stream it seems like it passes the smell test in regards to telemetry anyway. Clearly there's some fuzzy and vague shades of gray lines and the industry as well as the FCC seem to be turning a blind eye or simply wavering on digital communications as an emphasis to minimize bandwidth while maximizing data throughput with some tolerance towards obfuscation that digital technologies introduce.

I've been looking into whether the DJI Phantom 3 Lightbridge is actually "Encrypted" and everything I see on this suggests that the only lightbridge product which offers encryption is the Lightbridge appliance where you can activate / deactivate encryption and manage it's settings. It doesn't appear that there's any actual encryption in the DJI Phantom 3 pro lightbridge which would further support amateur usage of lightbridge if true.

 

[WetDog]

Interesting point and I suppose one worthy of clarification. Comments on using Amateur bands are limited to the scope of legal operation within licensed amateurs. While some members have commented about performing the DJI channel expansion mod for the sake of increasing range the truth is that all this mod would do is offer additional options when the user is located within a saturated environment in which the typical DJI channels are in use or experiencing undesired interference. This mod will not increase the power output of your radio transmitter. However DJI has by default limited the channel selections to legal unlicensed usage so unless the user is a licensed amateur operator there is no legal advantage of performing this mod and with the increased scrutiny of this hobby it is important for pilots to operate within legal guidelines.

For the Amateur operator this is a unique opportunity to enjoy an additional "Privilege" and escape some of the congestion pitfalls associated with the 13 cm band.

Back to the power comment, that's not what this mod is about and people should understand that. This mod will not give you increased power but it "May" give you increased range if you are able to acquire a down-link video frequency that is free of the interference associated with an alternate channel that you may have otherwise been stuck with.

Regarding amps; lol, that's just funny. Within the amateur band plan one could maximize the legal power and I think most of us already try and optimize our reception. But seriously the advantages of amplification would be in direct conflict with (What we have here in the states) the FAA's guidelines on flight within visual line of site so it's pretty much doa. Possible in theory but certainly not practical and I haven't read anyone in this thread to this point suggesting amps anyway.

In short this mod does provide limited potential for Legal Amateur Operators to navigate their video downlink frequency to hopefully a less saturated and available space, legally, which will perform better than a crowded frequency.

73's and happy flying

- Roger

Pretty much spot on, but --- amps could well be useful to punch over trees. I can lose video link in at 300 feet if I the signal has to go through any vegetation. 2.4 GHz loves them water molecules. But an edge case, limited to those of us who live in the tyranny of the green.

 

[Shammyh]

DJI Phantom 3 pro encryption:


I've been looking into whether the DJI Phantom 3 Lightbridge is actually "Encrypted" and everything I see on this suggests that the only lightbridge product which offers encryption is the Lightbridge appliance where you can activate / deactivate encryption and manage it's settings. It doesn't appear that there's any actual encryption in the DJI Phantom 3 pro lightbridge which would further support amateur usage of lightbridge if true.

https://dl.djicdn.com/downloads/phantom_3/en/Phantom_3_Professional_Release_Note_en_160407.pdf
https://dl.djicdn.com/downloads/phantom_3/en/Phantom_3_Professional_Release_Note_en_160407.pdf

That said... "encryption" could be like ROT13... or the DJI equivalent.

Hard to say what's going on in that SDR without dissembling the firmware updates in depth.

 

[Roger 2112]

https://dl.djicdn.com/downloads/phantom_3/en/Phantom_3_Professional_Release_Note_en_160407.pdf

That said... "encryption" could be like ROT13... or the DJI equivalent.

Hard to say what's going on in that SDR without dissembling the firmware updates in depth.

Hmm.. "Improved encryption to enhance security during transmission". Scratching my head on this one. If you think about encryption here it would seem that the concern would be someone hijacking the flight controls, who'd care about telemetry and video?? So I wonder which are they talking about as there are 2 separate channels.. <Shrug>

Thinking about it the overhead for encrypting and decrypting the live video stream would take some processor resources, power consumption and create latency on the video feed. They've got to be talking about flight controls.

 

[banana hammock]

Hmm.. "Improved encryption to enhance security during transmission". Scratching my head on this one. If you think about encryption here it would seem that the concern would be someone hijacking the flight controls, who'd care about telemetry and video?? So I wonder which are they talking about as there are 2 separate channels.. <Shrug>

Thinking about it the overhead for encrypting and decrypting the live video stream would take some processor resources, power consumption and create latency on the video feed. They've got to be talking about flight controls.

I would definitely say the "Command data field" of a transmitted RF Packet. My guess would be AES-256 w/ CRC-32 as the video streaming is likely accomplished w/ H.264 <MPEG 4> compression. I believe that you are correct in the overhead assumption.

 

[billy_LB2]

Glad to have been of help!

And thanks for taking the bones of my sheet and adding all the additional information and formatting!
Very much improved!

~~~

It's an interesting situation... where the "Lightbridge" is really just a SDR attached to a Davinci video DSP, with a fairly wide RF front-end. Lots of discussion/speculation about what exact protocol is in use for the video/telemetry side, but my money is on something similar to WiMax or DVB-T.

The baseband/radio itself is probably capable of running on a very wide variety of frequencies, though I have no idea how flexible that RF front-end really is.

Out of curiosity... as I'm not a ham/amateur operator myself... but as the "Lightbridge" signal is encrypted in some way or another... does that limit the ability to use it across amateur bands?

~~~

Also... the legal situation is interesting in broader terms. I have a few friends who are into ham, and they all (as you guys do clearly as well) take the rules very seriously. Little bit more seriously than I would... TBH.

OTOH, you have tons of folks on this forum using the "channel mod" and running channels 29-30, aka, 11.5-12 cm bands, with 2 or 3 watt boosters. Not only are those boosters not tuned for these frequencies, but neither are the antennas! Plus, this is clearly illegal under FCC rules.

Personally... I do bend the rules, and often use the upper end of the 2.4 GHz ISM, around 2490 MHz. Technically not okay... but the noise floor is significantly lower once you get just above WiFi, which for me, in an urban area, makes a huge difference. I also fly a little bit beyond VLOS (and lots of auto-pilot missions for photogrammetry, where I can't always see the bird), but the FAA is currently only politely asking that pilots stay in VLOS, it's not actually the law/rule, so I happily exploit that for now.

Anyway... just curious what you RF guys think about this situation... since to my knowledge, no one has actually come after a Phantom pilot for abusing/misusing the licensed RF bands. Also... most people running outside the spec frequencies are using fairly high-gain antennas... so not sure how that factors into it either.

What makes you believe the Uplink or Downlink is Encrypted? I actually dont believe the P3A through to Inspire's or Sparks, etc are encrypted. However the Higher End DJI AC, like the Matrice, most likely are using encryption.

Have you checked out the DJI GIT Hub on the WWW?