The only video output from the camera is HDMI. Since the video link is analog, this signal need to be converted to analog composite video. This is done by this cute little device; a HDMI-converter.For better range and reliability, I decided to use a 1.2 GHz video link rather than the usual 5.8 GHz.
The only video output from the camera is HDMI. Since the video link is analog, this signal need to be converted to analog composite video. This is done by this cute little device; a HDMI-converter.
The transmitter has an output power of 200 mW.
The video transmitter came with the normal monopole antenna. I decied to change it to a cloverleaf antenna. The cloverleaf antenna is omnidirectional, which means it transmit (almost) equally well in all directions. It has a wider signal pattern in the vertical plane than the monopole. This is good because we don't want to loose signal just because the multirotor is manuvering.
But the cloverleaf has another feature. While the monopole antenna is linear polarized, the cloverleaf antenna is circular polarized. A circular polarized signal that bounce off something will reverse polarization. This mean that the receiver antenna will attenuate the bounced signal while the direct signal is received unattenuated. This will prevent video disturbances known as multipath interference.
I prefer the three-loop cloverleaf over the four-loop skew-planar and the five-loop Mad Mushroom mainly because it is easier to make, but is is also ligther, has less drag and better standing-wave ratio (more efficient). The poor reverse polarization rejection does not matter for a transmitter antenna.
The receiver (center) and transmitter (left) as delivered, right out of the box.
Because I've changed the transmitters antenna to a circular polarizing, I have to use a circular polarizing receiver antenna as well. I could keep the monopole antenna at the expence of -3 dB attenuation, but I have something better in mind.
A helical antenna will not only receive circular polarized signals better, it is also a directional antenna meaning it will amplify signals from the direction it is pointed to. This means I have to point the antenna at the drone. This will not be a problem as long as the antenna is fairly short and wide-beamed. I'll aim for a 60° beamwidth. A more pinted beam gives better range, but has to be more precisely aimed.
To view the received signal I have a 7 inch TFT-monitor connected to the receiver.
The combination of frequency and antennas makes the video link by far outranging the 2.4 GHz command link. The reason for this is that if I have a uncontrolled flyaway, I will have video untill it comes down so I at least will have an idea of where to pick it up.