This article covers analog 5.8 GHz video first, because that is where channel planning is hardest, then mixing analog with DJI, Walksnail and HDZero. The channel sets come from Oscar Liang's FPV channel chart and from club and race practice. The legal limits are the EU's.
Before you plug in
Ask which channels are already in use as soon as you arrive. Oscar's advice is to choose a free channel as far from the occupied ones as practical. Many clubs formalise this with a frequency board. The Orange County Modelers Association in California is a typical example of the rules: every FPV pilot signs in and out on the board, nobody plugs in a quad on an unknown 5.8 GHz channel while others are in the air, and anyone changing channel tells the pilots nearby first.
Two habits help regardless of the rules:
- Power up in pit mode if your VTX supports it, then switch to your assigned channel and power. The article on Betaflight VTX control on this site covers pit mode and how to switch it from the radio or OSD.
- Set the channel manually on both the VTX and the goggles. Oscar warns that auto-search can lock onto a neighbouring channel that is "close enough" rather than the exact frequency. You get a picture, just with less range and more exposure to other pilots.
Why spacing alone is not enough
An analog video signal is not a single frequency. Oscar gives a bandwidth of about 30 MHz for an analog channel, about 20 MHz for DJI and Walksnail at 25 Mbps, about 40 MHz at 50 Mbps and 27 MHz for HDZero. Raceband, the band most pilots use, spaces its channels 37 MHz apart (R1 5658, R2 5695, R3 5732 and so on up to R8 5917 MHz). That is good separation, but Oscar says it does not mean all eight Raceband channels can be used at once without interference.
The second problem is intermodulation distortion (IMD). When signals from two transmitters mix, they create new frequencies, and one of those can land on a third pilot's channel. Oscar's example uses three channels that look well spaced: F2 (5760 MHz), F4 (5800 MHz) and F6 (5840 MHz). One common product is 2 × f1 - f2. For F4 and F2 that gives 2 × 5800 - 5760 = 5840 MHz, which is exactly F6. The pilot on F6 can get interference although nobody is on their channel. Evenly spaced channels are exactly the pattern to avoid with three or more pilots.
Tools such as RotorHazard's IMDTabler calculate these products for a set of frequencies and give the set a rating. A perfect set scores 100, and every product that lands within 35 MHz of a channel in the set lowers the score.
Channel sets that work
Oscar's suggested combinations, which take both spacing and IMD into account:
| Pilots | Channels |
|---|---|
| 2 | R1, R8 |
| 3 | R1, R4, R8 |
| 4 | R1, R3, R6, R8 |
| 5 | R1, R2, F2, F4, E5 |
| 6 | E4 (5645), E2 (5685), F2 (5760), A4 (5805), E6 (5905), E8 (5945) |
Clubs and races in many places use a six-channel set called IMD6C: R1 (5658), R2 (5695), F2 (5760), F4 (5800), R7 (5880) and R8 (5917). The Orange County club uses it as its fixed schedule and says the channels are "designed to work together" and are not to be deviated from. It also reserves F4 for fixed-wing FPV, a reminder that a club can add its own rules on top of a standard set.
Oscar adds that all these sets assume reasonably clean VTXs that do not bleed heavily into neighbouring channels, and that some of the frequencies may not be legal in every country. In the EU, many of them are not.
The EU limit: 5725-5875 MHz at 25 mW
EU rules on short-range devices (Commission Implementing Decision (EU) 2019/1345) harmonise the 5725-5875 MHz band for non-specific short-range devices at 25 mW e.i.r.p. Member states, Poland included, must allow use of the band on these terms. They may allow less restrictive conditions, so check your own country's rules if you need more. E.i.r.p. is the radiated power including antenna gain, so it is not just the number in the VTX power menu.
Compare that range with the channel sets above. R1 (5658), R2 (5695), R7 (5880), R8 (5917) and the whole E band lie outside it. IMD6C uses four channels outside the band, and every set in Oscar's table includes at least one channel outside it as well, because all of them use R1, R8 or the E band.
For locations limited to roughly 5725-5866 MHz, Oscar suggests a four-channel set:
| Channel | Frequency |
|---|---|
| R3 | 5732 MHz |
| R4 | 5769 MHz |
| B6 | 5828 MHz |
| A1 | 5865 MHz |
Working out 2 × f1 - f2 for every pair in this set, the nearest product lands 22 MHz from one of its channels. Keep in mind that with a signal about 30 MHz wide, R3 and A1 sit close to the edges of the band. Oscar notes that the narrower range generally limits how many pilots can fly at once. If more people show up, fly in rounds.
Digital systems sold in the EU have their own CE channel lists. Oscar's table gives three CE channels for DJI and Walksnail at 25 Mbps (5735, 5770 and 5805 MHz, plus the public channel 5839 MHz) and four for HDZero (5732, 5769, 5806 and 5843 MHz).
The 25 mW limit also takes care of power. Oscar's general advice for groups is 200 mW or less outdoors and 25 mW indoors, because lower power makes interference easier to manage. In the EU, 25 mW is already the licence-free limit.
Mixing analog and digital
DJI and Walksnail goggles both transmit as well as receive, so they can interfere with analog pilots standing next to them. Oscar suggests keeping digital pilots about 3-5 m away from the others as a starting point.
His other advice for mixed groups:
- Keep analog and digital channels as far apart as practical. A common approach puts analog pilots on low Raceband channels and digital pilots on higher digital channels.
- DJI and Walksnail pilots should use 25 Mbps rather than 50 Mbps when flying with others. 50 Mbps takes about twice the bandwidth and overlaps more neighbours.
- DJI and Walksnail units may briefly use their public channel 8 (5839 MHz) when the air unit powers up. The pilot assigned to channel 8 should power up last, and everyone should move off it to their own channel as soon as possible.
- Analog pilots should avoid R6 (5843 MHz) when digital pilots are around, because it overlaps the public channel.
At events with many pilots, Fly High FPV describes splitting rounds by video system: DJI pilots fly together, analog separately, HDZero separately, with DJI and Walksnail mixing best and analog and HDZero mixing well when there are not enough pilots for a full round.
Antennas help too
Oscar suggests putting pilots on neighbouring channels on opposite circular polarizations, one on RHCP and the other on LHCP. Opposite polarizations reject each other to a large degree, depending on antenna quality and axial ratio, the figure that tells you how well an antenna keeps its circular polarization. Each pilot's own goggles and quad must still match. The article on FPV video antennas on this site explains how much a mismatch costs.
Quick checklist for a group session
- Ask who is on which channel, or check the frequency board.
- Power up in pit mode, or only once you know your channel is free.
- Agree on one channel set for everyone flying at the same time, with no evenly spaced triples.
- In the EU, stay within 5725-5875 MHz at 25 mW e.i.r.p.
- Set the channel manually on the VTX and the goggles.
- Keep digital goggles a few metres from analog pilots, run digital at 25 Mbps and stay off R6 and channel 8.
- Announce every channel change before you make it.