I’ve been flying FPV for a couple of years now and I’ve build many ground stations. However these ground stations have always been cumbersome, fragile and/or not very pretty. Now I’ve finally tried enough configurations of antennas, receivers, diversity, tracking and so on to know what I want and need for my type of FPV flying.
The antenna I come back to time after time is the Helical. It’s perfectly circular polarized, extremely wide band, has a good beam width and looks cool. Its always worked flawlessly for me so that’s the antenna I’ll be using for my overkill ground station.
One thing I’ve come not to underestimate is the ease of transport. If a ground station is too cumbersome, fragile or has things that gets cough everywhere, you’re are much more likely not to bring your FPV gear on a trip, or whip it out quickly if you see something interesting. Thereby missing great opportunities to fly and catch good video. Therefore this ground station will be compact, robust, light weight and easy to carry. If I can carry my tricopter, transmitter, and ground station with ease to the car in one trip I’ll be satisfied.
The last thing I want this ground station to be is professional looking. I do not want to feel ashamed when I set up my gear at a video production set. With all that in mind, let me present my overkill FPV ground station. I’ll start of with the antenna itself. (To build you own helical antenna I can recommend reading this guide)
This is going to be the reflector plate for the antenna. It’s a stove burner cover made out of stainless steel which I found it in a cupboard at home (don’t tell my wife). In sweden the largest burner on a stove is 21cm in diameter and this cover happens to be 23.2 cm across at the narrowest point, which is exactly the size of a 1280Mhz reflector.
I used a dremel with cutting discs to remove the lip of the cover. The stainless steel is very tough and I used up 17 or so discs to get it of.
I drilled a hole for the active part of the antenna wire at the point where the coil will begin on the other side.
Pre tinning the stainless steel is a good idea as it takes a lot of heat and you don’t want to overheat the coax cable.
Soldered in place.
Back side. Notice that I’ve sanded the plate (I’ll be painting it later and want the paint to stick properly)
Front side. The active part of the coax poking through.
I decided to paint it orange. I’m very partial to orange and I think it will look great with the black parts.
Time to make the antenna coil. To do that we need copper. I had this cable laying around that will be perfect.
1mm thick solid core copper wire.
The spray can happened to have the right diameter for forming the coil. The object you wrap around should ideally be 15% or so smaller than the diameter your trying to achieve as the wire springs back out a bit after forming. The tape on the can is so that I get the correct coil spacing.
Coil all done. This antenna is going to be lefthand polarized hence the direction of the winding.
In order to make this antenna as though as possible I decided to make the the coil support extend over the edge of the edge of the reflector plate. Cut from 1.5mm G10 fiberglass on my CNC machine
This really made the antenna very strong and robust.
Back side of the antenna.
The glassfiber support was glued to the reflector plate using super thin CA.
The coil in place. Simply wound it through the holes.
The coil is well protected.
Helical antennas usually have an impedance of 100-140 ohm. Our FPV gear needs a match of 50 ohm. To achieve that you add a matching transformer. I used the IBCrazy’s tapered match on my antenna.
I used a SWR meter to achieve the best match possible. I added a lot of hot glue to toughen up the weak spot where the antenna cable and coil meet.
The antenna done! I must say it looks splendid.
The side panels and bottom that will make the body of the ground station fresh from the CNC.
I used small 10×10 wooden pieces glued to the sides and then screwed from the bottom to assemble the body. This will make it easy to take apart if necessary.
Removed the protective plastic. The text and lines have been milled down about 0.3mm and the plan is to inlay it with paint.
I used spray paint as it has close to zero surface tension and thus flows into the cracks very willingly.
Done! Looks way better than expected.
To be able to easily turn the ground station on and off, I decided to mount switches on the outside of the case.
I found these awesome safety switches on biltema (A swedish hardware/automotive store). Apart from looking cool they also prevent accidental on or off turning of the ground station. The reason why I chose to go with two separate switches was that these safety switches automatically switches back off when you flip down the lid again. Since that would make it even more prone to it being turned of by accident, I went with two separate switches and a relay with “self holding” circuit. More on that later…
This is the receiver I used. It’s a 12 channel 910-1360MHZ receiver from ReadyMadeRC.com with a upgraded saw filter
I like always knowing how much battery I have in all my gear. That is why I use the Aurora 9 with telemetry on all my aircraft. My ground station is no exception. So I decided to integrate a LiPo capacity checker.
The LiPo checker is automatically powered on with the rest of the ground station.
To have the two power switches work the way I wanted I needed to add a relay. I’ll try to explain in words how I connected everything. The OFF button is configured as normally closed. The ON button is configured as normally open. The positive wire from the battery is connected to the OFF button which is connected in series to the ON button. The ON button is connected in series to the coil of the relay. The other side of the coil is connected to the ground. So when the ON button is pushed the relay coil becomes energized and it switches it’s output. The center pin of the output on the relay is connected to the possessive wire after the OFF button. The normally closed output of the relay is connected to the all the ground station gear, but also back to the positive part of the coil on the relay it self. Which means that when you flip the ON switch the relay switches its output and then supplies it’s own coil, bypassing the ON switch. This is called a “self-hold”. As soon is the relay is turned on it stays on until the power is cut. This is done by the OFF switch which is normally closed, which means that it’s going to break the circuit when it is flipped. This simple circuit enables the ground station to be powered on without either switches being turned “on”, which means that the lids can be closed during operation.
Added some hot glue to protect the gear.
Since I quite frequently give “rides” to other people, I needed a second video output. This tiny video splitter from Flytron was perfect for this application. It works with 12V and it’s small. No nonsense, it just works the way it’s supposed to.
Here is the two video outputs. I decided to go with one servo connector for my custom video goggles and a standard RCA connector for the secondary output.
The servo connector also supplies my video googles with 12V, which is great as I don’t have to have a yet another battery to worry about.
Ready for action.
Built in angle of around 40°
Goggles hooked up.
The cable is protected nicely.
Secondary goggles plugged in.
Video goggles fits snuggly with no chance of falling out.
In the wild.
The ground station feels stiff yet light.
The display is very clear and easy to read.
Easy to change channels, but hard to do it accidentally. I only added to two frequencies I use.
Time to fly.
So far the new ground station has been a success. It’s worked flawlessly. It’s easy to transport. It looks good. It’s robust. The antenna is awesome. It’s also possible to take it apart for easier transport in suitcases, which was very nice for my US trip. I’m very glad I took the time to built it and I think I’ll use it for a very long time.
So what is your thoughts about it? What would you have done differently? Leave a comment and let me know!