Parabolic reflectors, do they really work?

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My set of Skyreat Aluminum Parabolic reflectors arrived this afternoon from Amazon.com. I could not wait to test them so I simply slipped them on over the existing stock antennas, powered up the Phantom 4 and flew out to 1,850 feet at 145 feet altitude. I had a clear line from the antennas to the drone and the signal registered 100%. I then turned around 180 degrees and noted that the signal dropped to 68%! All other variables were unchanged. I landed and again repeated the test to the same spot and altitude and got almost the same results. I noticed that as I turned around, the signal started dropping at about 30 degrees and at 90 degrees, the signal was down to about 80%. I am going to further test the array when I have more time with a Litchi waypoint mission out to about a mile, again with a clear line of sight between the RC and the aircraft. I will come back here and post the results.

Has anyone else performed any sort of testing with a similar array? So far, I consider this $16.00 purchase a very worthy investment.

Thanks,
Jim
WA5TEF
 
There have been tests and they do work. However, they don't boost the signal at all. They only more narrowly focus the signal to the Phantom. The result _may_ be a "cleaner" signal to the Phantom. The result of this _may_ be that the signal can cut through interference.

What you are most likely experiencing is that the antenna in the drone is changing it's relationship to the transmitter. This cane result in better/worse signal. More narrowly focusing the transmitter signal may not change this situation.

Keep in mind that other things can affect this as well, such as not pointing the reflectors directly at the Phantom. The channel you are using can also make a difference.
 
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Tcope, yes you are correct. I am very familiar with antenna theory and design. I have built many ham radio antennas and seen how they work, or don't work. One can better visualize the function of a directional antenna array by taking a partially filled balloon and applying pressure to one side and notice that the opposite side expands out. The more you squeeze the balloon into a narrow shape, the farther the balloon stretches but also the more narrow it gets. In other words, there is the same amount of air (power) in the balloon, only it is made to go mostly in one direction. I would guess that these reflectors produce about a 25 degree beam width pattern with very few minor lobes, which is wasted energy if it is not going to the drone. And, it is true that the orientation of the drone will alter the results a small amount, but by keeping it almost perfectly still as you know a Phantom can do, this result can basically be eliminated. That is one reason I ran the test the second time to rule out as many variables as I could. Also, some outside events may cause different readings, such as passing vehicles. As you noticed this mile long test that I am going to run next will tell us more about how well this array works. The transmitter in the RC unit has a limited amount of power, exactly how much I have not been able to find out. By putting this limited power where it is needed instead of letting it expand in all other directions is very wasteful. This concept is more clearly explained in The ARRL Antenna Book. The description of directional or phased antennas shows what can be achieved by simple modification of existing antennas. The stock antennas on the RC unit are made for an all round use and designed to work at least in many circumstances.

Do you perhaps know exactly which antenna is used for control and/or video reception? I would really be interested in find out this information for future experiments.
Thanks for your input,
Jim
WA5TEF
 
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Do you perhaps know exactly which antenna is used for control and/or video reception? I would really be interested in find out this information for future experiments.
Thanks for your input,
Jim
WA5TEF
On the RC as you hold it to fly, the left side is control signal transmit, the right side is video signal receive. You can learn more from my testing last year.
 
This afternoon, I tried another test of the parabolic reflectors. I flew at 200 feet and kept the drone pointed in the same direction all the way. The first stop was at 1000 feet and being pointed directly at the Phantom 4, the signal strength was 100%. I then turned to the 90 degree position and the reading was 97% and 180 degrees it was 87%. Next stop was 1500 feet where I got 100%, 91% and 74%. Then at 2000 feet it was 100%, 89% and 74%. Next it was 2500 feet it read 100%, 86% and 48%. At 3000 feet it was 94%, 76% and 51%. At 3500 feet it was back to 100%, 71& and at 180 degrees it disconnected. I went on out to 4000 feet and got 92%, 69% and again disconnected. At 4500 feet it was 80%, 74% and disconnect. Then at 5000 feet it was back up to 96%, 58% and again disconnected at 180 degrees. I am not satisfied with these results. The trend should have been down all the way, not up and down at some spots. I may have had a house almost block the signal past 4000 feet so I will find a different location and repeat the test. With the drone sitting at 200 feet altitude and out 3000 feet, I tried a different test. I held everything stead except I slowly rotated (yaw) the drone counter clockwise a full 360 degrees but did not notice any difference in signal strength which is strange because the on board configuration of the drone's antennas should be anything but omni directional. I want to repeat this test at maybe 7000 feet and see if I notice a change at that distance.
The flight patch was about 100 feet away from a public road and there were no electrical or phone lines visible. It crossed two creeks that had dense underbrush and trees but I believe I was high enough for that to not be an interference. It will be a few days before I can test again due to the severe weather we have moving into our area tonight and tomorrow and I will be tied up in our local weather nets. As soon as that is over I'll proceed to test again.

Thanks,
Jim
WA5TEF
 
This afternoon, I tried another test of the parabolic reflectors. I flew at 200 feet and kept the drone pointed in the same direction all the way. The first stop was at 1000 feet and being pointed directly at the Phantom 4, the signal strength was 100%. I then turned to the 90 degree position and the reading was 97% and 180 degrees it was 87%.
This is an interesting find. I presume you were using the Litchi app to measure and document the percentage signal.

I'm wondering which direction you "turned 90 degrees". If you turned clockwise, to the right, this makes sense.

The video transmit antennas are screwed up on the P4, IMHO. There are two video transmission antennas on the craft, both are on the left side of the craft (front left and rear left leg). On the P3 these two video antennas are kitty-corner from each other, which seems to be more logical to maintain a consistent signal as the craft yaws around.

This is easy to confirm using an RF meter to measure the signal strength, as the other legs have no signal. I've always wondered by DJI changed this antenna design, when the P3P worked great, but the P4, not so much.
 
This is an interesting find. I presume you were using the Litchi app to measure and document the percentage signal.

I'm wondering which direction you "turned 90 degrees". If you turned clockwise, to the right, this makes sense.

The video transmit antennas are screwed up on the P4, IMHO. There are two video transmission antennas on the craft, both are on the left side of the craft (front left and rear left leg). On the P3 these two video antennas are kitty-corner from each other, which seems to be more logical to maintain a consistent signal as the craft yaws around.

This is easy to confirm using an RF meter to measure the signal strength, as the other legs have no signal. I've always wondered by DJI changed this antenna design, when the P3P worked great, but the P4, not so much.
No, I was not clear on that statement. It was me turning 90 degrees and it was counterclockwise. I did later rotate the drone at 4000 feet I think but did not notice any signal fade as it rotated. I am going to test this more as I get time.
Thanks for your posting.
Jim
WA5TEF
 
No, I was not clear on that statement. It was me turning 90 degrees and it was counterclockwise. I did later rotate the drone at 4000 feet I think but did not notice any signal fade as it rotated. I am going to test this more as I get time.
Thanks for your posting.
Jim
WA5TEF
Oh, sorry I totally got the wrong impression of your test method. So you're saying that you pointed the parabolic dish away from the craft 90 degrees, then 180 degrees, correct? If that's how you tested the signal strength, I'm curious about relevance for this test, when the purpose of the Windsurfer is specifically to reflect and gather the signal in one general direction, a scheme to extend range.

Using this test method, it's not so interesting to me, since I don't understand the relevance. :D
 
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