Wireless video transmission is now pricewise reasonable. For roughly 150$ you can get a rather performing equipment.
We will only deal here with analogical video transmissions which are used by model-makers, more particularly for the FPV, therefore no video on IP, as it is not suitable for our use for the time being.
We should know that using radio frequencies is subject to regulations in each country. Some frequencies can be used by private citizens without prior authorization but under special conditions such as the emission power.
In model-making, since some years, radio communication is mostly performed on the 2.4Ghz (as the wifi). In order to avoid disruptions between the radio, the wifi and the video, we will then use a different frequency for the video, the 5.8Ghz.
In a basic system we will have:
– One caméra
– One vidéo transmitter 5.8Ghz
– One vidéo receiver 5.8Ghz
– One monitor or vidéo glasses
One standard model, which I personally use, consits in one TS351 transmitter and one RC305 receiver. Transmitters and receivers can be set to utilize various channels (frequencies closed to 5.8Ghz). We should be careful when we choose the transmitter and the receiver as the various brands do not exactly utilize the same channels.
I have also purchased recently one Mi600 transmitter which is compatible with my RC305 receiver
Once the transmitter and the receiver are set on the same channel, the video connection works without problems. However we can notice that the signal may be easily disrupted by any obstacle.
Once you have done your first connection, you will quickly notice the limits of antennas supplied by default. These omnidirectional stick type antennas are very sensitive to interferences and offer a very limited range.
But good news ! we can improve this
There are two main groups of antennas, the directional and the omnidirectional ones.
The directional ones
They allow an increased range but only work in a limited zone. It is then necessary to continously point your antenna at your drone.
The omnidirectional ones
They work in all directions (or almost) and are therefore very easy to use.Their limited range is a concern.
Instead of going through each antenna type, I will rather present you various possible configurations.
Basic ( omnidirectional stick type Antennas )
This is the configuration you will get when you will unpack your transmitter/receiver couple.This will enable you to perform some flight but with a limited range.About some tens of meters maximum with more or less interferences.
Stick + Patch
This configuration allows to significantly increase the connection range.Disadvantage the directional patch antenna must be continously pointed at your drone otherwise you’ll suddenly loose the connection .
Cloverleaf / Pinwheel
These antennas have the advantage to be omnidirectional and offer a very good resitance to interferences enabling you to obtain a very stable video connection within a reasonable range( 100 meters or more).
I personnaly use this configuration with antennas as these ones and I am very satisfied.
Cloverleaf / Pinwheel + Helix
In my opinion this is the ideal couple.Very practical as the idea is to obtain an omnidirectional transmission with the cloverleaf and a directional reception with the hélix antenna which offer a significant increase of the range ( we could normally exceed one kilometer).
The polarization of the antenna ?
You have perhaps heard about antenna’s polarization. We generally speak about circular polarization for the pinwheel / cloverleaf et helix antennas, and linear polarization (vertical or horizontal) for the stick or patch type antennas. You must absolutly use a pair of antennas which have the same polarization otherwise it will not really work properly……
The polarization orientation corresponds to the direction of antenna’s axis.
With a linear polarization, if your stick antenna is pointed vertically at your drone, you must also have a vertical polarization on your radio on the ground.When your drone moves or banks, the polarization is not anymore perfect.
With a circular polarization , whatever the antenna’s orientation may be, the polarization is correct, perfect then for model-making.
To overcome the problems of interferences and positioning of the antennas, there are vidéo receivers called « diversity ». They allow to receive simultaneously the signal of two antennas and swith on the best signal.
This enables you to have an omnidirectional + a directional antennas for reception and to receive the best of each antenna according to the conditions.
If you do not have a friend ready to continously point your directional antenna at your drone, it is possible for you to build an antenna pointer. It does consist in a mechanical system allowing to automatically point your antenna at the direction of the drone. To do this, your pointer must know his own position and to receive in real time the position of the drone( GPS position with a telemetrical connection for example).This is the best there is, but you must be a good expert and have a rather good budget to get involved in this type of realization.
If you wish to know more about it, I invite you to read this tutorial explaining how to realize an antenna’s pointer with Ardupilot : http://code.google.com/p/ardupilot-mega/wiki/AntennaTracking
As you can see, there are various possible configurations.The nice side of it, is that you can start with a simple pair of transmitter/receiver and then invest in your first antennas to improve your signal and then again, if you feel there is a need to switch on to directional antennas with or without pointer.
For the time being I utilize a pair of pinwheel/cloverleaf antennas, we will see if I decide to move further.
and you what is your configuration ?