All about Multirotor Drone FPV Video Transmitters

A Drone FPV Video Transmitter (VTx) is the workhorse of the FPV experience.  Over the last several years, we have seen a huge technological boost in how they perform, and the power output capable of the units, all in an increasingly smaller and smaller form factor.  Being mounted on the multicopter side of the business, they need to be able to fit into the space provided, be able to be connected easily into both the power distribution board and the camera, and be durable enough to withstand the abuse of many, many crashes.  While fitting that mold, they are easily one of the most sensitive parts on the multicopter as well.  VTx’s these days are feature rich, and sifting through those features can sometimes be overwhelming, but below we will detail those features to help clear up the inner workings, as well as help you select the best unit to for your particular application.

How does the Drone FPV Video Transmitter work?

Video transmitters work using similar technology to a radio, albeit in a much shorter range window.  At its most basic level, your onboard flight camera is connected into your video transmitter.  Your camera does the work of turning the images it is capturing into data, which is then sent into the video transmitter.  The video transmitter turns that information into a radio signal, outputs it to the attached antenna, which then sends that signal out.  The video receiver (VRx), attached to either your goggles or your ground station then captures that signal, coverts it back from radio waves into data, which is then shown on your display.  The range of your VTx is very dependent on a few different things; the power level of your VTx (rated in terms of milliwatts or mW), the antenna that is attached to your VTx, the antenna attached to your video receiver and the signal frequency that you are operating on.  

Note: There is no perfect setup for all of these things for all situations, however there are setups that work well for particular situations or for a majority of flight scenarios.

Power Output

The power output of a VTx is one of the most important factors of the unit, and is usually the first thing a pilot looks at when selecting one.  Most video transmitters for use on miniquads (250mm and smaller) are rated somewhere between 25mW and 800mW.  Normal logic does apply here (most of the time) when saying that the higher the rating, the further distance you can go from your base of operation and still maintain quality signal.  A higher rating can also mean that better signal penetration is possible (such as flying through a grove of trees) where on a lower setting, you would experience more signal breakup.  Also keep in mind that the higher the power output, the more heat that will be generated by the VTx, as well as more power consumed from your battery.  When flying at higher outputs, you want to get your multirotor in the air quicker so as to get air moving over the unit to cool it, otherwise the VTx may overheat.

Another factor when looking at power output is whether you plan on flying alone, or in a group of other pilots.  In a setting where you plan on flying with others, with multiple multirotors in the air at the same time, selecting too high of a power output can start to intrude on other pilots video signal, causing signal bleed over, which is never a fun situation.  Imagine flying your multirotor, and everything is going great, when all of a sudden another pilot’s video feed shows up in your goggles.  At first, it can be disorienting, even if it’s just for a second, and if longer, can result in loss of control in your quad, and a potential repair bill in your future.  This reason alone is why many clubs set both power and frequency restrictions when flying with them.  When flying with groups, a power output rating maximum of 200-250mw is often the recommendation, unless everyone is flying with higher output, then you want to match what your group is flying.

Drone FPV Video Transmitter Frequencies

VTx’s operate by sending your video feed over the air on certain frequencies.  Think of it more as tuning your car stereo to a particular station; you will not be able to receive that particular station until you turn the radio to the right frequency.  It’s the same for your VTx and VRx.  Both have to be set to the same channel in order to receive the frequency in its most stable form.  When selecting a VTx, first you are going to want to select one that will operate in the overall frequency spectrum that you are looking for.  For most applications, a 5.8GHz transmitter / receiver combo is going to fit just fine, however if you are going to go long range (anything over 1km) you may want to consider a lower frequency operating spectrum such as 2.4GHz or 1.2GHz.

Next, VTx’s are separated into bands and channels.  A band is a group of approximately 8 channels that you can choose from, spread out across the spectrum that you have selected.  As an example, a VTx may be built to use the Immersion RC band, which has the following channels: 5740, 5760, 5780, 5800, 5820, 5840, 5860, and 5880.  The channels are there for two reasons; to select the channel with the least amount of interference from the environment, and to grant the pilot the ability to fly with others.  Many pilots opt to select a VTx with a large amount of bands and channels available, to give them the most flexibility.  There are many options out there with up to five different bands and a total of up to 40 channels.

Note: When flying with others, a good rule of thumb is to separate each pilot by at least 60hz to avoid channel bleed over.  Example: When flying at 5800, other pilots should be flying on 5740 or 5860 at minimum.

HD Drone FPV Video Transmitter

HD video transmission is a relatively new technology when it comes to multirotors, and can definitely enhance the overall FPV experience.  Standard camera / VTx combinations while not lacking in detail, send and display video in a standard definition format, often around 600tvl (TV Lines) or 768 x 494 pixel resolution.  On a google display, this resolution works well, but if you were to size that image up onto a larger display, it might leave something to be desired.  HD video transmission is just that, they operate on a 1080p or 720p resolution, bringing a lot more life into your FPV feed.  This comes closer to that virtual reality feel that will give your flights that extra dose of amazing!  There are a few systems out there, but when looking at them, you want to make sure that you are going for a low latency system, as even a few milliseconds extra of lag in your feed could be the difference in your reaction time to an obstacle or gate.

Other features of a Drone FPV Video Transmitter

• Microphones – Some VTx’s have built in microphones that can send an audio feed down to the pilot.  Some pilots like this feature due to being able to hear what’s going on with the motors and props, and listen for any issues such as tune, or a part that might not be working as it should.
• Smart Audio – One of the newer features to the FPV world is smart audio.  This allows you to control the power outputs, bands, and channels of your VTx from your goggles or transmitter, allowing for on the fly changes, versus using the onboard buttons or dip switches to change options.  Definitely a useful feature!
• Power Filtering – There’s a lot of amperage flowing through a multirotor that’s in the air, and that can lead to some dirty power flowing through your FPV equipment.  There are several VTx’s on the market that have on board power filtering that will clean up that power before it reaches your transmission, giving you less static in your video feed.
• Pit Mode – This is a useful feature, allowing you to boot up your Drone FPV Video Transmitter in an extremely low power mode, which lets you change your band and channel without disturbing anyone currently in the air.  Transmission range in this mode is limited to just a few feet, and will not cause any kind of issue to others on higher power levels.
• Thermal Protection – A few VTx’s have the ability to limit power output as heat rises, keeping you from burning out your VTx while it’s sitting stationary on the ground.  

A few words of caution, or wisdom…

Remember, a Drone FPV Video Transmitter is a sensitive piece of equipment.  It is highly recommended that you do not… repeat do not, power on a VTx’s without an antenna attached.  These devices serve one purpose, to transmit video feeds out to the world, and they do that through the antenna.  When there is no antenna attached, that signal has nowhere to go, and can result in your VTx cooking itself, and releasing magic smoke…. It doesn’t smell so nice.  So don’t do it.