Phantom 4 Bird question Vtx power

[DnA_Pappas]

The Bird has 2 transmit antennas on left side and 2 receive antennas on right side. I'm assuming that the receive antennas are setup up for diversity or just in parallel to reduce flutter or weak spots. The transmitter is my question. Does anyone know how the RF output is configured? We are "supposed" to have .598mw of output power. Is that power divided into the 2 antennas or is each antenna being driven at .598mw? Some say that one transmit is video and the other is telemetry. I don't buy that because the telemetry could be embedded in a subcarrier of the video transmitter. If telemetry were separate, then there would to be another FCC filing for that as well. I don't have any way to measure the output power myself, and most testing I see others doing is just not accurate. So again my question is, is each antenna port putting out .598mw or is each port .299mw? Is each port driven by it's own output transistor or is the power divided on the board before it gets to the ports. Thanks for the help.
Dave

 

[wa5tef]

Good question! I’ve checked the received signal by covering one at a time and saw the signal drop signifantly. I assumed each antenna transmittedand received with alternate tasked assigned. Such as the control data was sent on one antenna and corresponding received telemetry came in on the other antenna. However I have not tested that idea. I have several devices to measure RF power out but only in the ham bands up to 450 MHz but I can modify one to get it into the 2,400 MHz range but it won’t be accurate, just a relative reading. However today I read a post mentioning that that the Phantom 4 had 5.8 MHz circuits also which I did not know! Then I read about “internal receiving antennas” that I don’t believe at all!
I’ll do some more experiments and report my findings back here. Thanks for starting this topic. It should yield some interesting comments.
Jim
WA5TEF

 

[DnA_Pappas]

Here's the facts in know to date. The P4,
Front and rear Left legs are video transmit.
Front and rear Right legs are both receive.
If the P4 loses Rc control signal, the P4 video transmitter turns off.
The video transmitter power is supposed to be .598mw. How is that power being used/distributed over 2 antennas?
The P4 has no 5ghz but the P4Pro does.

P4 controller
Control transmit is left antenna.
Video receive is right antenna.
Control transmit output power is supposed to be .303mw.

I believe the lower output power on the controller has to do with Rf exposure limits and your proximity to the transmitting antenna. If you look at the acc filings for the P4, it states that it meets the 20cm distance requirement for Rf exposure at it's power level of .598mw. So I'm assuming by Dji lowering their output power of their controller allows the operator to be closer to the transmitting antenna (less than 20cm) as opposed to the P4.

 

[DnA_Pappas]

Anything thing I noticed. In the Fcc filings for the P4, the P4 is listed as a MIMO device. This means it has more than one transmit signal (video/telemetry?). It would help to know what is happening on each transmit antenna port.
Just for clarification, when I say P4 I am referring to the bird, not the controller.

 

[wa5tef]

Interesting info. But, is the control transmit output power correct at 0.303 milliwatts? Even at 2.4 GHz that seems like a very low transmit power. Just wanted to be clear on that.

Just how would one go to the site that has this interesting data??
Thanks
Jim
WA5TEF.

 

[DnA_Pappas]

Interesting info. But, is the control transmit output power correct at 0.303 milliwatts? Even at 2.4 GHz that seems like a very low transmit power. Just wanted to be clear on that.

Just how would one go to the site that has this interesting data??
Thanks
Jim
WA5TEF.

Look for the fcc Id number on the bottom of your controller and enter that number into a Google search. It will bring up the fcc documents for that unit. Look for the one inside the battery compartment on your Bird too because that one is different. If you click on the PDF documents you can see the test reports and test photos.

 

[DnA_Pappas]

Interesting info. But, is the control transmit output power correct at 0.303 milliwatts? Even at 2.4 GHz that seems like a very low transmit power. Just wanted to be clear on that.

Just how would one go to the site that has this interesting data??
Thanks
Jim
WA5TEF.

And yes, that is supposed to be the output power of the controller. Many people believe it's actually lower than that because of the consistent decline in distance that you can travel before losing signal. It seems that with every new model and new firmware update the distance lessens. I can't confirm this because I don't have the proper equipment to test this theory. If you notice the message at the top of your screen when you start to lose signal, it says "control signal weak" and then after you start losing video. It's very rare to see the "video signal transmission weak" message because the Bird transmits more power at a higher altitude. When the Bird starts receiving a weak control signal, the video transmitter on the Bird starts turning off and on, which is why it seems you lose your video at the same time you lose your control signal. The Bird will only transmit a video signal if it has a control signal. I don't know why, or what purpose it serves for it to do that, but it does. I did order a 4 watt amplifier for my controller, and I installed it on the transmit side. I now lose video signal before my control signal. Distance has increased dramatically because now my limiting factor is the video transmitter. I don't know how far the control can get but I'm sure it's pretty far. My goal isn't really distance though, or more for local penetration through trees and such. I would like to amplify the video transmit somehow, but space is limited and no one is really sure about what each transmitter port does. I think it would be better to use one circular transmit antenna for video but I'm not sure if the two ports are the same signal or not, so I don't know if they can be combined to one.

 

[wa5tef]

Pappa’s, interesting thoughts. With DJI’s secretiveness about their hardware specifically I Doug you’ll be able to dig up much data on them and the drones. If someone could obtain an English version of the schematics something could be learned how it all works together. I’m sure the Chinese don’t want their drone technology to be known to us (USA). I’ll keep watching here hoping someone can get this information. Thanks for posting!!
Jim
WA5TEF

 

[wa5tef]

Pappa’s, interesting thoughts. With DJI’s secretiveness about their hardware specifically I Doug you’ll be able to dig up much data on them and the drones. If someone could obtain an English version of the schematics something could be learned how it all works together. I’m sure the Chinese don’t want their drone technology to be known to us (USA). I’ll keep watching here hoping someone can get this information. Thanks for posting!!
Jim
WA5TEF

And, thanks for the info on the numbers. I’ll check that out!!
Jim
WA5TEF

 

[Nu2dron]

And yes, that is supposed to be the output power of the controller. Many people believe it's actually lower than that because of the consistent decline in distance that you can travel before losing signal. It seems that with every new model and new firmware update the distance lessens. I can't confirm this because I don't have the proper equipment to test this theory. If you notice the message at the top of your screen when you start to lose signal, it says "control signal weak" and then after you start losing video. It's very rare to see the "video signal transmission weak" message because the Bird transmits more power at a higher altitude. When the Bird starts receiving a weak control signal, the video transmitter on the Bird starts turning off and on, which is why it seems you lose your video at the same time you lose your control signal. The Bird will only transmit a video signal if it has a control signal. I don't know why, or what purpose it serves for it to do that, but it does. I did order a 4 watt amplifier for my controller, and I installed it on the transmit side. I now lose video signal before my control signal. Distance has increased dramatically because now my limiting factor is the video transmitter. I don't know how far the control can get but I'm sure it's pretty far. My goal isn't really distance though, or more for local penetration through trees and such. I would like to amplify the video transmit somehow, but space is limited and no one is really sure about what each transmitter port does. I think it would be better to use one circular transmit antenna for video but I'm not sure if the two ports are the same signal or not, so I don't know if they can be combined to one.

Come on now Chaps,
Why not just fly your birds and enjoy them instead of being concerned about the ins and outs of a cat’s arse?