DIY Diversity Ground Station for FPV flying...with hysteresis

1:06 PM giovanni 0 Comments

Now that the tricopter is on its way to become my FPV platform I found myself stuck with the ground station being my video receiver strapped to a tripod with a rubber band, the screen tucked in a carton box, held in place by more rubber bands, with cables everywhere.
This not only takes almost 8 minutes to set up, but also makes everyone laugh.

After sometime of this going on I decided I had enough, and to take my "ground station" one step up. All in my RCLab style though, which means avoiding all unnecessary expenses, maximizing efficiency, and having a great deal of fun while doing it.

So, please, let me introduce you to the RCLab Diversity Ground Station:

The DIY Diversity Ground Station right before take off


Ok, first of all, what the heck is "diversity"? Well, it is nothing too fancy, but it is something incredibly nice to have. Especially if you can have it for a few bucks.

It is called diversity (controller) a system that analyses and compares the quality of two or more incoming signals (in this case video signals) and chooses the best one to output to your screen or video goggles.
This comes very handy when you want to run two different antennas on one single system.
For example in my case, I am running a cloverleaf, which has great signal reception when flying all around you, but it is somewhat limited in range, and a DIY helical, which only picks up signals which comes straight at it from the front, but it has a far bigger range.
This means that if I am flying close and around me the diversity controller will lock on the cloverleaf, but if I want to get a bit further out (in front of the antenna, remember), it will see that the quality of the signal coming from the cloverleaf is less than perfect and switch to the other receiver giving me always perfect video signal.

Thanks to Bruce Simpson over at RCModelreviews.com and Gilcd85 over at RCGroups.com I was able to build my own controller for under $10, instead of forking out more than $100 for a commercial one.
Please check out Bruce's video here to understand the process.

Firstly I tried to solder all the components on a breadboard, but it did not work, so I found out that Gilcd85, a member of RCGroups.com, had designed a board and by uploading it at OSHPark.com you can have three of them shipped at your door for $7.70. Isn't it amazing.

These are the three boards I received for less than $8 from OSHPark.com and they are awesome.

As Bruce explains in his videos, you need a couple of electronic components to have it all work:

For the basic version:
- 1x CD4066N Integrated Circuit (about $1)
- 1x LM324N Integrated Circuit (about $1)
- 2x 47k resistors (maybe $0.1)
- 2x 4.7k resistors (another $0.1)

For the "deluxe" version add:
- 2x LEDs (I don't think I paid more than 20c)
- 2x 330Ohm resistors ($0.1)

For the "super deluxe" version, which includes hysteresis (a system that dampens the switching process between the video signals) you also add:

- 2x 0,1μF capacitors (they were expensive, about 10c the couple...lol)
- 1x 1M resistor (I think I got that one for free)


A closer look to the brain of it all: I soldered all the components on in about 30 minutes. It is pretty easy.


Then I went on and built a small plywood box to hold all the components I would need. It is pretty small, and I bolted a tripod mount underneath it to be able to lock it in place in seconds...not 8 minutes.


The box I quickly put together to contain it all. It is very small: about 12cm x 6cm x 6cm and it is made of plywood.
The screw you see in the middle holds the tripod mount on the bottom

The components that I used are the following:
- 2x Boscam RC305 5.8GHz video receivers
- 1x Turnigy UBEC 3A
- 1x Diversity controller
- 2x red LEDs (optional)

The components that I am using: 
1) a switch. Pretty unnecessary but I love switches so why not.
2) a voltage regulator which brings voltages from 2S LiPos (8V) up to 4S LiPos (16V) down to the 5V I need.
3) the first Boscam RC305 5.8GHz video receiver.
4) a red led to tell me wether receiver 1 is on. (totally unnecessary again, but I happen to love LEDs too)
5) the brain: the $3 DYI diversity controller
6) the second Boscam RC305 5.8GHz receiver.

And here it is all inside the box, it is starting to look goooooood!

Once the lid is closed you can still access the channel switches. I am not sure of the usefulness of this, but hey, why not.

The interface: the two bright red LEDs tell me that everything is working fine, whereas the other two tell me which one of the two receiver is picking up the best signal.


Obviously, with two receivers you also need two antennas (that is the whole point, right?) so I went on and built myself an helical antenna. 
There is SO much to say about antennas (and so little i know) that I will skip the lesson here, and just give you a very general statement: the more turns your helical antenna has, the less wide the band will be (it means that it will only pick up a narrow radio frequencies range), the narrowest the reception angle will be but the furthest you can fly.
Helicals generally go from 3 turns (wide reception angle, mid distance and pretty wide band) to 12 turns (you know, narrow band, narrow cone and BIG distance). 
I built mine with 3,5 turns (it is actually a mistake: I was aiming at 4, but cut the wire short...) because I fly a tricopter so I am more interested in wide angles rather than great distances. But I might build a 8 turns to see what it looks like.

I found template and instructions in this video by Andrew Mcneil. 

This is the 3.5 turns 5.8GHz helical I built. I am pretty happy with the result considering it is my first antenna. Tests at home showed a far better signal compared to the spironet, but only if the antenna was pointing pretty much straight towards the transmitter.

Another view, with both the antennas on. I am not sure why the cable on the helical looks so weird, but rest assured, it is an optical effect.