Every FPV pilot has had a bad picture: snow, lines, a black screen, somebody else's view in their goggles. The good news is that the picture itself tells you what is wrong. Each kind of bad picture points at a different part of the system. Learn to read it, and you stop guessing.
The video chain
Your picture travels along a chain. The camera sees the track. The video transmitter (VTX) turns that into a radio signal, and the antenna on the drone sends it into the air. On the other side, the antenna on your goggles catches it, the goggles turn it back into a picture, and finally your own eyes have to see it clearly. If any link breaks, the picture gets worse. Half of that chain sits on your head, so before you blame the drone, rule out the goggles.
Read the picture
- Snow: the signal is weak. Look at the antennas, the distance, and what is in the way.
- Lines that follow the throttle: electrical noise from the motors and ESCs.
- Someone else in your picture, or bars rolling through it: another pilot on or next to your channel.
- Black and white, or a picture that rolls: the camera and the goggles are set to different video standards (PAL and NTSC).
- Black, but the OSD numbers still show: the camera or its cable. The VTX is working, because the numbers come through it.
- Clean, but blurry: this isn't the signal at all. It's the lens, fog, or the focus of your goggles.
Snow: the signal is weak
Check the antennas first. Most snow comes from an antenna that is broken, loose or wrong, either on the drone or on your goggles. FPV antennas are circularly polarised, either right-hand (RHCP) or left-hand (LHCP), and both ends must be the same. Mix them and you lose most of your signal. You usually can't tell them apart by looking, so check the label. An antenna with a cracked tip or a loose connector can look fine and still fly badly. And never power up a drone without its antenna: the VTX has nowhere to send its power and can burn out.
Then look at what is between you and the drone. At 5.8 GHz the signal doesn't go through much: bodies, walls, reinforced concrete and trees all block it. Flying behind something, or far away, gives you snow.
At HOBIzone we never fix snow with more power. Our rule is 25 mW, always, in practice and in races. Fix the antennas instead.
Lines that follow the throttle
If thin lines run across the picture and get worse every time you punch out, it isn't the radio, it's electricity. Motors and ESCs make electrical noise, and it travels through the wires into the camera and the VTX. Watch your DVR: if the lines come and go with the throttle, it's noise.
The usual fix is a low-ESR capacitor soldered across the main battery pads, with legs as short as possible: around 470 µF on a small build and up to 1000 µF on a 5″, rated above the voltage of your fully charged battery. Wiring helps too: camera and VTX on the same ground, powered from the flight controller rather than straight from the battery, and kept away from the ESC. When you test on the bench: props off, always.
Was it someone else?
If your picture was fine and then suddenly wasn't, look around before you look at your drone. A ghost image, bars rolling through the picture, or somebody else's view in your goggles means two video signals are too close in frequency. Maybe someone just plugged in on your channel, or did a "quick test" in the pits. Maybe two pilots are on channels right next to each other. Ask "who just plugged in?", check the channel screen, and spread out across raceband.
It's not always the drone
Your goggles have antennas too, often two, and they need the same checks as the drone: not bent, not loose, the same polarisation. Your head is also in the way. If you turn your back on the drone, your own head blocks the signal and the picture breaks up, so face the track.
And keep your head up. Many pilots drop their chin low without noticing, and that aims the antennas the wrong way. A patch antenna on the front of the goggles then points at your feet instead of the drone. An omni (the stick on top) sends and receives out to the sides but almost nothing off its tip, and with your chin down, that blind tip points towards the drone. It looks like you are trying to ruin your own picture, but most people don't realise they're doing it.
If the picture is clean but blurry, it isn't the signal. Set the focus and the eye distance (IPD) on your goggles, wipe the camera lens, and give the goggles a moment to clear if they fog up when you come into a warm hall from the cold. If the picture is grey or keeps rolling, check that the camera and the goggles are set to the same standard, PAL or NTSC.
Find it like a detective
Good troubleshooting is a habit. Change one thing at a time, and test after every change.
1. What kind of bad? Snow, lines, ghost, grey, black or blurry. 2. Drone or goggles? Try a friend's goggles on your channel, or your goggles on a friend's drone. Now you know which half is broken. 3. Antennas, both ends. Tight, straight, the same polarisation. 4. Settings. Band, channel, 25 mW, pit mode off, PAL or NTSC. 5. Wires and parts. The camera cable, solder joints, the capacitor. Swap one part, and test again.
You don't need perfect video
Race video is rarely clean. There are four drones in the air, a hall full of walls and people, and a rival right next to you. The best pilots fly through the static. Fix what you can before the race, keep flying during the heat, and afterwards check your DVR and fix the next thing.
We fly frying pans: nobody else is cooking. Bad video is something you can make better, not somebody else's fault.
Read the picture. It tells you where to look.
Read
- GetFPV: Diagnosing and fixing bad FPV video
white and black line static, multipath, antennas, VTX heat, jello. - Unmanned Tech: FPV video static, diagnose and fix
a checklist in the order to check things. - Unmanned Tech: RHCP vs LHCP explained
why both ends must match, and why you check the label. - Unmanned Tech: noise lines and capacitors
sizes and where to solder it. - Oscar Liang: power filters for VTX and camera
where electrical noise comes from.
For trainers: the 10-minute plan
| Time | Slide | Talking points |
|---|---|---|
| 0:00 | Title | Ask: "Whose video was bad last week?" Hands up. "Did you find out why?" Most people just change something and hope. Today we learn to read the picture. |
| 0:40 | Fig. 1 | The chain: camera, video transmitter (VTX), antenna, the air, the antenna on your goggles, the goggles, and you. Any link can break. Half the chain is on your head, so rule out the goggles before you blame the drone. |
| 1:40 | Fig. 2 | Six kinds of bad picture, six different suspects. Snow = weak signal. Lines that come with throttle = electrical noise. Someone else's image = channels. Black and white or rolling = PAL/NTSC. Black screen but the OSD numbers show = camera. Clean but blurry = not the signal at all. |
| 2:50 | Fig. 3 | Snow: check the antennas first, on the drone and on the goggles. They are RHCP or LHCP, and mixing them loses most of your signal. A cracked tip or a loose connector looks fine and flies badly. Never power up without an antenna: the VTX can burn out. Then: what is between you and the drone? Bodies, walls, concrete, trees. We never fix snow with more power: 25 mW, always. |
| 4:10 | Fig. 4 | Lines that get worse when you punch out are electrical noise from the motors and ESCs travelling through the wires. Check your DVR: do they follow the throttle? Fix: a low-ESR capacitor across the battery pads, short legs, 470 to 1000 µF, rated above the pack voltage. Camera and VTX on the same ground, away from the ESC. Props off on the bench. |
| 5:20 | Fig. 5 | Fine, then suddenly bad? Look around before you look at your drone. A ghost image or rolling bars means two pilots are too close in frequency. Someone did a quick test in the pits, or two pilots sit on neighbouring channels. Ask "who just plugged in?" and spread out on raceband. |
| 6:20 | Fig. 6 | The goggles have antennas too, often two, and they need the same checks. Keep your head up and face the track: chin down points the patch antenna at your feet and the omni's blind tip at the drone, and your head blocks the signal too. Blurry but clean is focus or eye distance, a dirty camera lens, or fog when you come in from the cold. Grey or rolling: set PAL or NTSC the same on camera and goggles. |
| 7:20 | Fig. 7 | Be a detective. What kind of bad? Drone or goggles? (Swap with a friend: your channel in their goggles, their drone in yours.) Antennas, both ends. Settings: band, channel, 25 mW, pit mode off, PAL/NTSC. Then wires and parts. One change at a time, test after every change. |
| 8:40 | Fig. 8 | Perfect video isn't the point. Race video is rarely clean, and the best pilots fly through the static. Fix what you can before the race, keep flying in the heat, check the DVR after. We fly frying pans: nobody else is cooking. |
| 9:30 | Remember | "Read the picture. It tells you where to look." |
Demo: Bring two drones and two pairs of goggles. Show the swap test live: goggles A on drone B, goggles B on drone A. Then hand round a damaged antenna and a good one, and let the kids find the difference. Props off the whole time.