When it comes to flying FPV, having solid, clear video signal is an absolute “must.” If you can’t see where you’re going, you’re not going to be able to fly. While our first reaction to solving this problem might be to add “more power,” as our friends at Tool Time would say, what we find is that the better solution is to actually improve our antenna setup. By focusing on your antennas first, by choosing the best antennas for your needs, you will be able to improve your FPV performance by leaps and bounds. Adding more power will only help marginally if you are not using the appropriate antennas for the job.
There are many different types of video antennas, each that have their own best case scenario of use -- all antennas have different pros and cons, and better and worse situations in which they should be used. Note that there is no “one solution fits all”; instead, you should analyze each situation and choose the best antennas for the job.
Before we go into the different types of antennas and how to choose which one is the best for you, let’s define a few terms that will be useful for understanding the differences between each antenna type.
Antennas disperse a signal that is broadcast and received based on “overlap”, to oversimplify it. To get the best performance possible, you want polarization on both RX (receiver) and TX (transmitter) antennas to match at all points during your FPV flight. If your antenna systems are mismatching, or the polarization doesn’t support acrobatic flight, then you will quickly notice signal degradation. Within polarization, you can have left-hand, right-hand, and linearly polarized antennas. Left and right-hand antennas will provide the best signal strength at all flight angles (banking/flipping etc), and linear polarized antennas will work well when both RX and TX antennas are oriented in the same way (i.e. level flight).
Measured as “dBi” or “gain relative to an isotropic source”, gain is a measurement of the “directivity” of an antenna. The higher your gain, the better your signal strength and the longer distance it will beam/receive, but it will also be directed in a particular direction. In general, a lower gain antenna will have a higher FOV (field of view) and the higher the gain, the antenna will have a lower FOV. In general, a lower gain antenna will be used on the TX, and a higher gain antenna will be used on the RX. In this way, the copter can transmit at all directions, because it may be facing any direction relative to the groundstation, and the groundstation will most likely remain stationary, and it’s beam signal will be more predictable.
The frequency of each antenna is determined by a few measurements on each antenna. Common frequency “bands” are 1.3mhz, 2.4mhz, and 5.8mhz. Each of these “bands” are broken into different frequencies: for example, some frequencies in the 5.8mhz “band’ include 5745, 5800, and 5945. It’s within a frequency that your “channels” lie, on a particular set of frequencies that form “raceband” for example.
Different measurements of wire and bends that form the antenna determine the frequency of the antenna. This plays into the size of your antennas. Most racing quad pilots fly on the 5.8 frequency. Because frequencies are determined by the length of wires on your antennas, it becomes cumbersome to use the lower frequencies. The lower your frequency, the larger your antennas will become. As a result, a 1.3ghz VTX antenna becomes as large as the quad you’re flying.
A “directional” antenna is generally a high-gain antenna that has a low FOV. so that FOV has to be pointed in the “direction” that the machine will be flying. Conversely, an omnidirectional will have low gain, and doesn’t require being pointed in a particular direction.
So now that we’ve established a baseline of definitions, let’s apply them to many of the popular antenna types, so that we can understand how best to use each.
Probably the simplest type of antenna, and is popular only because it’s the type that by default comes with your RX and TX. The “rubber ducky” antennas are simple antennas that use a single filament of exposed wire to determine video frequency. These are linearly polarized antennas, and only work well when the RX and TX antennas are oriented in the same direction. However, when the machine tilts or rolls, then signal will degrade quickly.
This is the most popular antenna for FPV flying. Circular polarized antennas can be either left-hand or right-hand polarized, and have a low gain, which means they will transmit in all directions and almost all angles. As a result, having a circularly polarized antenna on your TX on your machine is the best-case scenario, as it will provide the best possible signal at all possible angles. In addition, it’s a popular choice of antenna on your RX, as it means you’ll be able to fly all around yourself. You only need to make sure that your antennas are both polarized in the same direction.
A patch antenna can be left-hand, right-hand or linearly polarized, so make sure you know which is which when you’re flying with one combined with a circular polarized antenna. They are high-gain antennas with a low FOV.
A helical antenna is a circularly polarized directional antenna with a low or high FOV, depending on the build type. Helicals can be built longer or shorter, depending on the need. A longer helical antenna will have a lower FOV and a higher gain, and a shorter antenna would be the opposite.
The average FPV setup has two antennas, many have 3, and few have 4 or more. All antenna systems for FPV racing should have a circular polarized or dipole on the TX, with circular polarized being highly prefered. Then, on the RX end, if you know you’re only going to be flying in front of yourself, and relatively low, it’s best to choose a directional antenna. On the other hand, if you’ll fly all around yourself, circular polarized would be best.
Better yet would be to upgrade to a diversity ground station, which means that your ground station would become a 3 antenna system. A diversity RX will work to choose the best video signal between two antennas on the RX system. As a result, it’s possible to have a directional antenna pointing the way in which you will mostly fly, and an omnidirectional available to receive from all directions.
For longer range flights, you would want to have an antenna on your RX that would be high-gain and highly directional so that your signal is improved and your range increased.
As you can see, there are many different choices to be made when considering an FPV antenna system, and figuring out the best combination of antennas for your particular needs will exponentially improve your FPV experience. Play around with some different antennas, and start experimenting with what will get you the best signal.