What Are VRx Yagis and VTx Yagis?
What Are VRx Yagis?
VRx is shorthand for Video Receivers. VRx yagis are therefore video receiver yagi antennas. The term is specific for video systems on drones. If we were talking about cloverleaf antennas, they often have 3 clovers for transmission but 4 clovers for receiving because of the generally higher resolution signal being sent to the receiving antenna. (Note, though, that this is a matter of preference, not a necessity.)
What makes something a VRx yagi? It is generally going to be a yagi antenna receiving signals from the drone.
Since first person vision or FPV is generally 1.2 GHz, 2.4 GHz or 5.8 GHz, a VRx yagi will be one made for one of these frequencies. A major point in favor of yagis is that they don’t suffer much interference, since they’re made to receive a very narrow frequency. For example, the yagi below only receives 2400 MHz to 2450 MHz.
The downside of a yagi antenna over a wheel antenna is that it is directional. You’re going to have to make sure your controller is pointed at the drone and its antenna to be able to receive its signal.
The higher the frequency, the smaller the antenna. That makes higher frequency antennas of all types popular in drones. Note that you don’t necessarily have to choose between directional antennas like yagis and quad patch antennas in drones and omni-directional antennas like wheels. You can mount four directional antennas in a circle so that your drone can receive commands from any direction while still benefiting from minimal interference; this has the side benefit of extending your range. However, the 4 way power divider is very tricky; after losses in the divider, you end up with the same amount of signal as the omni-directional antenna.
What Are VTx Yagis?
VTx is shorthand for Video Transmitters. VTx yagis are therefore video transmitter yagi antennas. This term is pretty much only used for video systems on drones. The VTx antenna is sending video from the FPV camera to a video receiver, though this may be part of FPV goggles or a monitor.
What makes an antenna a VTx yagi? It simply needs to be a yagi antenna designed to transmit signals to or from a drone. In general, the VTx yagi is on the drone and relaying the signal back to the controller and video recording system. The VTx antenna is in the drone, sending back that high resolution image if you aren’t going to save the video to a local memory card.
In general, 5.8 GHz antennas were popular early on because they were so small and light. However, they tended to be connected to basic, analog equipment. This isn’t compatible with HD video, much less action cameras.
However, the analog video is actually preferred if you’re sending video back for navigation. Digital video is usually compressed. It takes time to compress the data stream, and then time to un-compress it. Imagine driving your car in high speed traffic; you have no windows, just high resolution TV cameras and screens. No major problems yet. Now drive in traffic with a 1 second delay … good luck avoiding an accident. That's why they like to have an analog video signal back to the pilot and thus send analog video signals in real time back to the pilot.
You can increase the range of the drone by increasing the power through the antenna. A high power VTx system will also give it more reliable signals when flying solo. However, trying to extend range by pumping more power through it drains your battery and generates extra heat. This is another reason why many drone operators opted for yagi antennas that work on very narrow frequency ranges, minimizing interference and maximizing range while needing very little power.
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© 2018 Tamara Wilhite