The fibre optic FPV

Fibre optic FPV drones are making their presence felt in Ukraine, this new type of drone is harder to defeat than previous types and production is likely increasing. This article provides an insight into how these drones work and how they are made. 

Spend enough time on social media with an algorithm as ugly as mine and the footage will probably be familiar. It starts with a grainy video feed, several error signs are flashing on the screen and the tips of two propellers are just visible at the edges of the screen with a large copper wire cage protruding to the front. A beige field is visible below with an olive green armoured vehicle moving through it, there’s a cage contraption built around its turret and a few soldiers lounging on the front of the hull, their legs dangling down over the side, ready to jump. The FPV (First Person View) drone speeds up, moving towards the figures who at some point hear the whine of its four electric motors struggling to carry the weight of the PG-7 anti-tank warhead and the extra large battery that it’s carrying. The soldiers jump down and run, but the FPV operator is focused on the armoured vehicle. It’s a BMP-2, designed to carry infantry, it has a 30 mm cannon and relatively thin armour. At the last moment, the video feed cuts out and the viewpoint switches to another drone, the reconnaissance drone that has followed the BMP-2 and its crew from their hide in a nearby woodblock. The scene has been edited as the unit operating the FPV is using it to secure funding from its online community for more drones and equipment. The PG-7 didn’t struggle with the armour of the BMP-2, it’s designed to penetrate much tougher targets and a fire has started inside the vehicle, two crew members can be seen climbing out, the fate of the third is unknown. 

Fibre optic FPVs: Jamming

This scene, or ones like it, have been repeated tens of thousands of times in Ukraine, and thousands of others that started like this will never be seen. The reason in many cases is that the command link between the drone and the operator was suppressed by electronic warfare. The video feed, and the operator’s instructions to the FPV are sent via radio frequency, often in the 2.4 GHz and 5.8 GHz bands, which are also the bands that Wifi routers use. This wireless connection carries data digitally encoded on radio waves to the drone – things like bank left, or more power to motor 2 – and the drone returns data encoded to the operator including the video footage and the constant warnings that it is low on battery. This fragile connection can be disrupted by a nearby system emitting in the same radio frequency bands. To understand how this works, imagine that you are listening to country music from a few hundred metres away. It’s a good volume and you’re able to talk to a nearby friend about your weekend plans. This is a healthy unsuppressed connection between an FPV and its operator. Now imagine that someone sets a new, much bigger and louder speaker up right next to the country music, instead of the mellow tones of Carrie Underwood, this speaker plays death metal – loud. You can’t hear the country music any more, you can’t really even hear the death metal, you can’t hear your friend. This is how electronic jamming works: it drowns out the signal either at the operator’s end, or at the FPV’s with signals that are much more powerful (and also measured in decibels), so that the FPV stops receiving instructions or the operator stops receiving video and the drone crashes. 

Electronic warfare provided a form of protection against FPVs and other small drones, it was not perfect, nor could it ever be. Both sides in Russia and Ukraine update the firmware and frequencies of their drones on a regular basis, which means that the jamming protocol that worked last week might be worthless today and a new one must be found. However, a new development has begun to take hold in Ukraine, the fibre optic FPV. These drones still use radio frequency signals to operate, but they aren’t sent via fragile radio waves carried through the air, instead they travel over a fibre optic cable that is spooled underneath the drone. The signal is now unjammable, there is no way for an electronic warfare system to insert its own signals into the link between the FPV and its operator. This situation is like listening to country music on the world’s best noise cancelling headphones, in your own house. The death metal can be played outside, but you’re not going to hear it. This is probably one of the more significant changes brought about by the fibre optic FPV, without jamming, Russian and Ukrainian soldiers will be reliant upon finding cover, out-running the drone’s battery, or shooting it down with a personal weapon, which is also very difficult. There are some developments in the works across the world to better counter small drones in the last line of defence, you can read about one – the AD-LER shotgun cartridge from Norma here. But in general, the fibre optic FPV is going to be difficult to counter once it reaches its destination. 

Fibre optic FPVs: Design

This video from Avenge Angel shows how a fibre optic FPV is set up and made ready to fly, as well as the wires used in this design. Credit: @AvengeAngelcom

Adding a spool of fibre optic cable requires changes to the typical FPV design. A typical FPV is a relatively robust drone, especially when compared to a DJI Mavic or shop bought drone, hard plastic gives way to carbon fibre in many cases, and tougher propellers. The motors will be high powered and coupled to a large battery pack giving high top speeds over 100 km/h but short flight durations measured in seven minutes or so. The payload is limited to a few kilos, which includes the munition, camera, and antenna. With a fibre optic FPV, there are a few changes that must be made to this design template. 

This first is that the frame for the drone has to be bigger and stronger because a fibre optic spool can weigh up 1.5 kg to 2 kg, depending on the range required. However, the company Avenge Angel advertises fibre optic FPVs with carbon fibre spools weighing just 800 g for a range of 3 km, and 1.25 kg for 5 km. So, the frame has to be bigger to accommodate this as well as the camera, motors, battery and munition. The spool is typically attached to the bottom of the drone, underneath and away from the propellers, which can break or cut the cable if they come into contact. With the frame strengthened, uprated motors capable of carrying the additional weight of the spool and munition are needed. Drones are assessed on their max take-off weight, which is dictated largely by the thrust generated by the propellers.  So, more weight requires propellers that generate more thrust compared with other designs. This may not be an issue for FPVs designed to carry smaller, anti-personnel payloads, but larger strike packages like a PG-7 grenade will demand greater thrust from the motors. This in turn drives a greater demand for power to keep the drone in the air. 

The fibre optic cable itself will consist of up to five wires for communicating between the drone and operator. This includes one each for receiving and transmitting signals, one for the video, one for voltage, and an earth. The cable, although made of glass, can be relatively strong but pilots must take care not to snag it on trees or obstacles during flight and this can reduce manoeuvrability compared with a wireless FPV, which in turn could make the drone more vulnerable to small arms fire. At the same time, the fibre optic cable means that the drones can be deployed when friendly electronic warfare systems are actively suppressing the other side’s own radio controlled drones. The absence of any broadcasted radio frequency signals also means that the drone can’t be detected using spectrum analysers – think of the music analogy above. This, and the noise of the engines and propellers, is typically how FPV drones are detected. One final benefit of the fibre optic cable is greater bandwidth to pass data back to the operator, which can mean lower latency on the video feed and higher fidelity imaging, all of which help with identifying and engaging targets. 

Fibre optic FPVs: Tactics

The Russians have used fibre optic FPVs to fly behind Ukrainian lines and position the drones close to likely vehicle routes, landing them and turning the motors off, thereby preserving battery life. As Ukrainian vehicles approach, the motors are switched on and the vehicle engaged, a Ukrainian officer told the Counter Offensive Pro newsletter in early November. They can also be seen using the fibre optic FPVs to slowly observe Ukrainian positions before being used for a strike or to bring alternate assets into play. Otherwise, they are frequently used to target vehicles moving on a road, in a similar fashion to traditional FPVs and loitering munitions. This tactic exploits the movement of vehicles rather than trying to locate them in their hides, which are often well-camouflaged and protected. It is also worth noting that some of the apparently successful attacks that get published are likely the work of several FPVs, some Russian accounts claim a single T-90M withstood 100 FPVs, even if it was actually a tenth of that number, this shows the level of effort that can be required to defeat a heavily armoured vehicle. 

Calibre comment

The use of FPV drones and now fibre optic control links has developed rapidly in Ukraine as a result of the survival pressures in that conflict. Their use has spread to Syria most likely with Russian assistance, and it is highly likely that they will be used in many future wars to come. However, it is important to be balanced when assessing their impact. Many FPVs fail, either mechanically because of the construction or technically because of the warhead failing to detonate. They also do not guarantee a vehicle defeat, despite offering the ability to optimise an approach angle. It is also likely that active protection systems such as Rafael’s Trophy or the Sentinel system from Artis will be able to intercept drones – indeed, the BAE Storm Crow and Terra Raven systems appear to be designed to achieve exactly this. For a western force, this may mean that heavy armoured vehicles are better protected against these threats than they may seem from the many tanks and IFVs that have been immobilised and eventually defeated by FPVs in Ukraine. They will remain, however, a consistent threat to infantry whether in buildings or the open, which will mean further adjustments to doctrine and tactics, as well as new equipment to help minimise the impact of FPVs. 

By Sam Cranny-Evans, published on 12th December, 2024.