P3S 5.8ghz Controller RF Signal Bi Directional or Not?

[frenky600]

Excuse guys if with my empirical tests or at least performing with a little radio knowledge they made it confusing. Let me first tell you what I did, starting from the assumption that I initially thought that all my problems came from transmission from drone to rc.
After doing tests with two p3s and two remote controls where a p3s went a distance of 400 meters original and my 40 meters. Reversing and relinking the situation has not changed so the main culprit in my opinion has become the drone.
At this point with great difficulty I did lend a field detector with range up to 10gz. The detector had a display with various types of indications but I just looked at that dbm.
I did two measurements off by first isolating an antenna on the drone leg with foil paper I set the detector filter (with many difficult menù) and the result was 17dbm. I released the first antenna and measured the second which gave 2.3 dbm.
Thinking that the drone would transmit then I thought the transmitter was burnt or that the second antenna was just receiving.
I do not know if I got in harmony and I do not know if the test I did was regular or just another time loss.

 

[frenky600]

I sincerely trust more of your experience than an empirical test carried out with foil paper and a field detector of 300 €.

 

[robca]

Completely unscientific test: I have an FPV receiver with a band scanner. It scans all the 5.8GHz FPV frequencies and displays signal strength in a channel with a bar (intensity of the signal in that band). It's clearly not a real frequency analyzer, but it works well within its limitations. I have a basement that is pretty much a Faraday cage, so very limited stray 5.8GHz signal there

If I turn in just the TX, I can clearly see the frequency hopping signal (i.e. various bars in various channels, always changing frequency). If I turn on only the drone, there's no signal I can see.

So, either the drone is not transmitting, or transmitting at a very, very low power (if Frenky600 17dBm is to be believed, it would be a pretty low signal for a TX supposed to work at P3S distances), or the drone transmits only if a RX signal is received (which would not make much sense, frankly)

But, on second thought, I think I have a definite answer

Looking at this https://www.scotttorborg.com/img/4165/phantom3-standard-teardown-00701.jpg, you can see the drone 5.8GHz module. The main 5.8GHz chip used is a transceiver, so capable of both TX and RX https://www.hobbielektronika.hu/forum/getfile.php?id=291458.

But if you look at the other chips, you can see two LNA SKY65404 http://www.skyworksinc.com/uploads/documents/SKY65404_31_201512K.pdf which can only be used for a receiver (Low Noise Amplifier).

The last SMD chip is marked S20, and that is an antenna switch http://www.skyworksinc.com/uploads/documents/201097E.pdf. If you follow the traces, clearly you can see the signal moving from the two antennas to the two LNA in series, to the main chip.

The BK5811 also seems to have the two outputs simply terminated (to avoid problems), but I can't be sure of that without using a multimeter on the actual traces (which do not plan to do )

So there's no way for that module to transmit with enough power (the chip by itself can only do 2dBm max, which is 1.5mW, really nothing for the distances in play). I feel pretty confident that the 5.8GHz signal is monodirectional, from the Tx to the drone

As a counterproof, look at the Tx module https://www.scotttorborg.com/img/b355/phantom3-standard-teardown-00501.jpg and how different that looks, since it clearly is a TX-only module. So, once again, even assuming that the drone is somehow transmitting, there's no way for the TX to actually receive anything

 

[OrlyP]

Excellent job robca! I think that's fairly scientific.

Can't go wrong with the chip specs. The transceiver chip used on the aircraft, as you deduced, is probably just designed for RX-only, with the TX function crippled. Anyway, the remote controller using RX-only chips pretty much concludes that the 5.8GHz is a simplex communications (remote controller to aircraft).... as opposed to the half-duplex 2.4GHz signal.

 

[frenky600]

Very exellent analisys!!!! this is the start point to follow the famous range p3s problem on rc signal. Now i still wait for new drone pcb with receiver also. I would like to make some new test with two pcb.

 

[Frank Pliska III]

EXCELLENT ANALYSIS ALL.
Outstanding info.
Thanks Much
Mot. Eng.

 

[frenky600]

Now that I understand how things work about the 5.8 and 2.4 transmission, I'm not sure I did the right thing by purchasing a new pcb part 96. Maybe I should concentrate on return of the rc signal through 2.4 ghz. I think The transceiver circuit of the 2.4 is mounted on the gimbal ***'y. What do you think about?

 

[frenky600]

At this point. I'm very confused. Why one rc with first bird reach 500m stock and the same rc with my bird still reach 40m like with my rc? Where is the problem? Bird receiver? 2.4 signal strength telemetry for 5.8 transmission? What is the right way to solve? how many questions on my mind.

 

[Ozz]

The last SMD chip is marked S20, and that is an antenna switch http://www.skyworksinc.com/uploads/documents/201097E.pdf. If you follow the traces, clearly you can see the signal moving from the two antennas to the two LNA in series, to the main chip.

Slightly aside - there are reports bypassing this S20 antenna switch chip solves the range problem many P3 owners are having...

Phantom 3 Standard range mod , let's do it together...