Antenna Improvements for My Budget Drone

I am a very much a novice when it comes to drones and flying them, but, I recently bought a Kai One Pro/Max GPS 8K budget drone. Because I like to know what makes things work I have pulled the whole UAV apart and put it back together again. This under $300 budget drone doesn't meet up with the specs of the sales pages, but it's been a fun drone to fly. I bought this drone because it has a lot the functionality of the expensive drones and it also has an SD card slot, which is the main reason for buying this particular model. I understood that the FPV videos and camera shots back to the phone are not the best quality, and I wanted the, apparently, better images sent to the SD card.

Having purchased it and testing the features I found that it was capable of reaching around 300 metres in distance and the Video signal back to the phone was cutting out around that point. So I decided to make some modifications to it to try and improve the signal quality and distance. Being an ex Radio HAM I am very familiar with transmitters and receivers, and antenna designs and their capabilities. So this was a fun challenge for me.

What I noticed when I opened this drone was that it had 3 antennae (aerials) - one for the remote controller control (2.4GHz) and two for the FPV video and phone controller App (5.8GHz). All three antennae were tucked inside the fuselage in horizontal positions. For the best signal strengths antennae need to be orientated the same way. Vertical type antennae, such as these, transmitter and receiver, should be kept vertical. So, the first thing I did was to take the antenna wires out of the fuselage to do some tests. I believe I improved both the distance and the video stability beyond 300 metres to around 400 metres. The only problem with just having the antenna wires outside the drone was that they were still not properly vertical. Improved, yes, but really needing to be held in place with some sort of sleeves mounted to the body of the drone. I left this to think about it while I did some research on drone antennae. I found that people were favouring the cloverleaf designs for antennae and they are very easy to make at home. There are a number of videos and tutorials online on how to make these antennae so I'm not going to cover that in this project. Suffice to say that I modified the remote controller to accommodate a screw on socket to mount different types of external antennae (such as the common WiFi antenna found on home internet routers). I then made a cloverleaf antenna for the remote controller (2.4GHz), as you can see in one of these images. Guess what! The drone's distance was extended to nearly 600 metres when the Video signal cut out completely, causing the drone to automatically go into Return to Home (RTH) mode.

So that's the reason for this project - which was to try and extend the quality and distance of the video signal. I'm happy with the 500 metre range for the drone because it is totally out of site at that distance and I doubt if I'll ever need to fly that far..

The only parts needed for a project like this are:

1. The two Lollipop antennas operating in the 5GHz band
2. A 100mm length of 20mm PVC conduit.
3. You'll also need a junior hacksaw and a heat gun or hair dryer

5GHz is the band that the FPV video uses on this drone. I got these lollipop antennae at AliExpress for around $20 delivered. They arrived in 10 days.The connectors on the cables need to be IPEX to fit the little sockets on the drone's video board.

The antennae themselves are both RHCP (Right Hand Circular Polarized). You can get LHCP options but in my case it doesn't matter. If I could fit similar to the phone then I would have to use the same polarization on both sides.

These lollipop antennae are basically tiny cloverleaf designs (see the cutaway image). They could be homemade too but they are pretty cheap to buy.

While the basic vertical antenna has a radiation pattern in the shape of a doughnut, the cloverleaf design has a better one and possibly gives a small gain in signal strength too.

Removing the 2 antennae is very straight forward. The cover plate on the bottom of the drone is opened and the 2 boards (SD card slot board - top and the Video Transmit and Receive board - below) are exposed. Very carefully lift these up and to the side without stressing the cables attached. Using the end of a small screwdriver, lift (unplug) both coax cables from the board.

I lifted the two boards out of the way so I could drill a 3mm hole on each side to run the coax cables through. I made sure the boards were out of the way when I drilled the holes - the last thing you want is for the drill bit to go into a cable or board component. First I tried behind the screw posts that hold the little cover on, but the coax cable on the lollipops is too stiff to bend around inside the drone and get to plug onto the antenna sockets on the video board. I then drilled the holes as far forward as possible and this worked. If the antenna wires(coax) were much thinner, like the original antenna cables are, it would be easy. Anyway after a bit of fiddling I got it connected.

The lower video board has a heatsink stuck on the bottom with a sticky two-way thermal transfer tape. This has come loose and is no longer sticky. As I don't have any of this tape in my electrical supplies I used what I had - Thermal Paste. I coated the loose thermal tape with some paste before placing the boards back in (I have put some images in of both Thermal Paste and Tape). The electronic shops do keep the paste for transistor and computer processor mounting. They may also have the tape, but one can get it on eBay.

I am super pleased with the completely new idea I have had to support the lollipop antennae.

I was in the workshop considering reshaping a part of an electrical PVC box to make up the channels I was considering to hold the cables for these antennae. Then I spotted a length of 20mm PVC conduit I had. I had a brainwave! The lollipop diameter was just smaller that the 16mm ID of the pipe, so I measured off two 50mm lengths and cut the profile you can see in these images. I cut a slot (gap) in the 20mm tube, then used a heat gun (I'm sure a hair dryer would do) to soften the PVC and adjusted the diameter to just smaller that the lollipop (so it would be a secure, spring fit). Worked beautifully! Then I shaped the stem and also bent it into shape with the heat gun to fit nicely on the body of the drone.

I am amazed at how easy it is to soften and reshape this electrical PVC conduit material using a little heat.

The last thing was to glue the lollipop supports onto the drone. I used standard PVC plumbing glue (see image). I first put a small amount of acetone (use can use the standard plumbers PVC primer) onto both the drone and the holder. This gets the surface sticky and will improve the gluing. Then I applied a little PVC glue to the antenna support and held it in place for about 10 seconds. I then let it dry (cure) for a few hours.

To fit the antennae into the holders I held my thumb tightly over the cable where in goes into the drone body so the cable would not move and come off the internal connector. Then I bent the cable while pushing the lollipop into the holder from the bottom.

As you can see the drone's arms fold in beautifully. I'm very pleased with the finish and the lollipop holders are secure and strong.

As it is, the drone's legs will now need a short extension (about 5-10mm) which I'll work on.

I still want to make and fit a thin tube to hold and secure the 2.4GHz antenna further back. Then all the wires will be secure and held vertical.

I have put together a personal website for the progress I've made. You can see more of what I have been doing with this drone this at this address, https://kaionedrone.wordpress.com

Well at last I got a sunny day with only a little wind to take a new flight distance check. I can report that again I'm super pleased with my lollipop antenna modification on the drone. I think the drone reached around 750 metres when the phone cut out. I had video all the way with no problems as you can see from this image and video. What I don't understand is that I got no flight recording on the phone App this time, so I can't say what the final distance was. I took a couple of screenshots and stopped and started the video a few times before the signal was lost. I think that is why this video isn't showing forward movement - I was fiddling with the phone to take the screenshot before pushing it further to where it cut out. The wobble of the video is probably because of the breeze it was trying to stay steady in.

Video quality was set to 720 P (1280x720)

I must say that I am so pleased the RTH brings the drone home faithfully.

So now I'll work on securing the 2.4GHz antenna to the fuselage and add some leg lengths.