RF power measurements

[John Locke]

I've been disappointed in the P4 signal integrity of the stock radio. I know people have been getting some good range with various antenna enhancements, and I generally use a surfer also (I just bought the Itelite antenna), but I'm joining the camp of Gadget Guy and wanted to express my disappointment in DJI's continued reduction in power output of Lightbridge. I'm perplexed why DJI would do this, I really don't think they exceeded RF power guidelines from the FCC for the 2.4Ghz band they're using for Lightbridge, yet the evidence shows they are gradually lowering the power of the RC. Go figure.

With my P3P (bought July 2, 2015) I never lost control signal first, I would always lose video signal first. However with P4 I often lose control signal first, sometimes triggering RTH. My flying is always LOS, no trees, away from the city, such as ocean flying, local hills, in safe areas.

Out of curiosity I bought an RF meter to read the output power of my radios. This isn't a super accurate method I admit, but it's a ballpark representation of what's going on I think. These results appear to match the FCC filings by DJI, saying they are lowering the RF output.

It appears the P4 has the weakest control signal since Phantom started using Lightbridge. This explains my experience of getting NO SIGNAL scenarios with P4, when I don't have that experience with my P3P in the same area I fly all the time. Sometimes my P4 drops control signal for a couple seconds, sometimes over 3 seconds, which triggers RTH.

When I took these measurements the numbers jumped around a little, but what I show here is pretty much the average of the numbers for each unit. I got number higher and lower for each the RCs, these photos represent an average.

It appears getting an Inspire controller for our P4 is the hot ticket. I can tell you from first hand experience that I've been amazed at the improved signal integrity with the P4 craft using an Inspire controller, the range is great in comparison to the stock P4 RC. It's interesting the P4 craft shows slightly more video output power than the P3P. That's promising, but the P4 RC control signal is what's so bad IMO. Using the Inspire RC I've gone 12,000 with no surfer and not a glitch. But using the P4 RC I'm lucky to get 5000' before I start getting NO SIGNAL notices, intermittently.

BTW, the P4 and P4 RC have the latest firmware.

 

[Dacon Productions]

For the RC RF readings, were the sticks in "up" neutral conditions or did you move them around?
When the RC sticks are in neutral position, the RF Tx is minimum since it not telling the drone to do anything and the drone just hovers in place.
Can you repeat the test but this time move the sticks around pretending you are flying and average the Tx power readings?

 

[John Locke]

For the RC RF readings, were the sticks in "up" neutral conditions or did you move them around?
When the RC sticks are in neutral position, the RF Tx is minimum since it not telling the drone to do anything and the drone just hovers in place.
Can you repeat the test but this time move the sticks around pretending you are flying and average the Tx power readings?

I enabled RTH on each RC to make sure something was being transmitted. Moving the sticks around didn't seem to make much difference, which I found strange.

 

[Dacon Productions]

Also as I know, the legs function are as follow looking at the drone from the:
BACK
Left is Rx from the RC
Right is Tx to RC (video)
FRONT
Left is Rx from the RC
Right is Tx to RC (video)

 

[Dacon Productions]

Strange...moving the sticks around should give you a higher Tx value than in neutral. How was the Tx on the Inspire C RC?

 

[Dacon Productions]

Can you look at your RCs and drone FCC IDs and compare the published Tx versus the reading you got? Curious if they are close. I only have the Inspire C RC and the original P4 RC that I never use.
FCC database shows Inspire C RC at almost 0.8W, the most powerful RC so far.
FCC ID Database Search

 

[With The Birds]

Can you look at your RCs and drone FCC IDs and compare the published Tx versus the reading you got? Curious if they are close. I only have the Inspire C RC and the original P4 RC that I never use.
FCC database shows Inspire C RC at almost 0.8W, the most powerful RC so far.
FCC ID Database Search

If the op is going to have any hope of replicating the results in the FCC application he will need a test setup like this (and kniwledge as to how to enter engineering mode on RC and AC)...

 

[N017RW]

When the RC sticks are in neutral position, the RF Tx is minimum since it not telling the drone to do anything and the drone just hovers in place.

That makes absolutely no difference it transmit power.

 

[N017RW]

If the op is going to have any hope of replicating the results in the FCC application he will need a test setup like this (and kniwledge as to how to enter engineering mode on RC and AC)...

No, RF power is a conducted measurement.
The posted setup shown is for other measurements.

 

[John Locke]

Also as I know, the legs function are as follow looking at the drone from the:
BACK
Left is Rx from the RC
Right is Tx to RC (video)
FRONT
Left is Rx from the RC
Right is Tx to RC (video)

That's incorrect. For the P4 the left front and left rear are video transmit. However P3P uses front right and left rear for transmit, which makes more sense to me, oriented diagonally across from each other.

 

[John Locke]

If the op is going to have any hope of replicating the results in the FCC application he will need a test setup like this (and kniwledge as to how to enter engineering mode on RC and AC)...

I had no intention of replicating, that isn't the point. I only wanted to compare between various RCs and craft. This basically shows how they compare with each other, and it confirms what I had suspected.

 

[With The Birds]

No, RF power is a conducted measurement.
The posted setup shown is for other measurements.

I'm aware of that. The setup depicted is probably to measure out of band emissions. My point was the cheap device and methodology employed in the exercise subject of this post is unlikely to arrive at, or at least have any hope of reproducing the test conditions providing for the DJI documented power outputs that accompanied the FCC application.

 

[ringolong]

Thanks for sharing!

 

[WWK888]

So John, do you think getting the Inspire RC would be better than modifying the P4 RC with a boosted system? I like the idea of keeping it stock looking and therefore be able to use my present foam insert for my backpack. $429 for a new Inspire RC and probably about the same or a little more for a boosted system (installed).

 

[Dacon Productions]

Will jump in here a bit.
My first drone was a P3P with B type RC. Reading all the threads about RC Tx and which type has what, I decided to buy off the net an Inspire RC type C since it has the most Tx power.
If you can find, the first P3P RC was type A that also has good Tx power, almost as much as the Inspire type C RC.
I am not a fan of RC mods, sails maybe but nothing else. The only reason I can see to get the new Tx cables and amps is if you want to fly from inside the house or car. Remember, even if you have unlimited Tx power, you can only fly about 8 miles round trip being limited by the battery capacity.

 

[jstjohnz]

I measured peak power output on the RC port (P4 RC) of 10-11dBm, or 10-12mw with a RigExpert IT-24.

 

[John Locke]

So John, do you think getting the Inspire RC would be better than modifying the P4 RC with a boosted system? I like the idea of keeping it stock looking and therefore be able to use my present foam insert for my backpack. $429 for a new Inspire RC and probably about the same or a little more for a boosted system (installed).

I've decided to mothball my P4 RC and use my Inspire GL658A RC for my P4. I went out this afternoon and flew the P4 5000' with the P4 RC when I started losing control signal. Using the Inspire RC I went 11,000' over the same terrain before I started losing control signal. Both tests were without a surfer, Ch32, 4mbps bitrate. I will be adding the Itelite antenna to the Inspire RC, but won't be using amps for field flying, I just don't like all the bulk and extra battery when I can likely get a 3mi range without the amps. I'm fine with 3mi, batteries won't last long enough to go much farther. However, I will experiment with Jeremiah's car antenna setup with amps at some point, since I'll have the "clean install" SMA connectors in the Inspire RC, ready for the amps and cables. I have ideas about using that setup in my RV. I think using the Inspire RC offers a better starting point, instead of using the weakest Lightbridge RC ever. If you're going to buy an Inspire RC it may be a good idea to look for the GL658C as mentioned, given the reported higher transmit power.

 

[WWK888]

Thanks for the input.

 

[Stealthmatt]

I've been disappointed in the P4 signal integrity of the stock radio. I know people have been getting some good range with various antenna enhancements, and I generally use a surfer also (I just bought the Itelite antenna), but I'm joining the camp of Gadget Guy and wanted to express my disappointment in DJI's continued reduction in power output of Lightbridge. I'm perplexed why DJI would do this, I really don't think they exceeded RF power guidelines from the FCC for the 2.4Ghz band they're using for Lightbridge, yet the evidence shows they are gradually lowering the power of the RC. Go figure.

With my P3P (bought July 2, 2015) I never lost control signal first, I would always lose video signal first. However with P4 I often lose control signal first, sometimes triggering RTH. My flying is always LOS, no trees, away from the city, such as ocean flying, local hills, in safe areas.

Out of curiosity I bought an RF meter to read the output power of my radios. This isn't a super accurate method I admit, but it's a ballpark representation of what's going on I think. These results appear to match the FCC filings by DJI, saying they are lowering the RF output.

It appears the P4 has the weakest control signal since Phantom started using Lightbridge. This explains my experience of getting NO SIGNAL scenarios with P4, when I don't have that experience with my P3P in the same area I fly all the time. Sometimes my P4 drops control signal for a couple seconds, sometimes over 3 seconds, which triggers RTH.

When I took these measurements the numbers jumped around a little, but what I show here is pretty much the average of the numbers for each unit. I got number higher and lower for each the RCs, these photos represent an average.

It appears getting an Inspire controller for our P4 is the hot ticket. I can tell you from first hand experience that I've been amazed at the improved signal integrity with the P4 craft using an Inspire controller, the range is great in comparison to the stock P4 RC. It's interesting the P4 craft shows slightly more video output power than the P3P. That's promising, but the P4 RC control signal is what's so bad IMO. Using the Inspire RC I've gone 12,000 with no surfer and not a glitch. But using the P4 RC I'm lucky to get 5000' before I start getting NO SIGNAL notices, intermittently.

BTW, the P4 and P4 RC have the latest firmware.

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Can you try testing the P4 remote again with the latest 2.8.3 IOS app and see if the results have changed?

Also are you able to test the power output with out connecting a signal to it? When I see you near the legs/transmitter, it doesnt look like you have any incoming signal to it? what mode is that?

 

[John Locke]

Can you try testing the P4 remote again with the latest 2.8.3 IOS app and see if the results have changed?

Also are you able to test the power output with out connecting a signal to it? When I see you near the legs/transmitter, it doesn't look like you have any incoming signal to it? what mode is that?

My testing is only measuring transmitting power.

For the craft, I measured video transmit power. Each craft was sending video to the RC's with iPad Air2 running Go app 2.8.3.

For the RC, transmitting measurements were taken with RTH enabled on each RC to make sure it's sending a control command. I tried stick input but the RTH seem to work more consistently, so that's what I used as a baseline for comparison purposes.

FYI, the Go app isn't going to change transmit power from the craft or RC. The RF output is fixed in the RC and craft so it complies with the FCC filings that DJI committed to. DJI cannot adjust the power outputs after filing with the FCC a fixed output number. However the new Go App may streamline the processing (H.264 decompression) of the video to be more reliable, but it doesn't change the power outputs.