Channel calculator for FPV drones to find channels with enough separation.
No GUI exists - it's a simple Java app that should be compiled and run.
In order to change params - modify them in the source code and run.
There are several reasons not every channel can used when multiple pilots fly simultaneously:
-
Channel separation - if two channels are close together then video receiver has hard time distinguishing between two signals, especially since no VTX are perfect and they all produce signal spread
-
Intermodulation distortion (IMD) - when two VTX work simultaneously on frequencies F1 and F2 there would also be 2 additional peaks on
F1*2 - F2andF2*2 - F1frequencies -
Harmonics - 5.8Ghz VTX produce harmonics on F + 190Mhz and F + 240Mhz (can't find reason for this - but they can be seen during spectrum scan)
In order to fly comfortable we must choose channels that are far away from all these peaks.
This app simply searches for channel sets that satisfy specified separation parameters.
Note that largest peak is usually from other channels, the IMD peaks are smaller and harmonics are even smaller, this should be taken into account when choosing separation gaps (harmonics gap can be set to zero for example if everybody has good vtx). Although on some VTX we've seen quite large harmonics peaks - you could almost see another pilot's video on a higher channel.
In some countries channels E4, E7 and E8 are illegal to use and are locked in some VTX.
In order to use them in Betaflight - you have to mark E band (or any band) as CUSTOM instead of FACTORY. This will make FC send command to VTX to set specified frequency (any arbitrary frequency can be set) and not command to set channel predefined in VTX.
Some VTX are hardware locked and have to be unlocked to support CUSTOM bands.
For whoop-style 25mW VTX in confined space separation should be at least:
- 25Mhz between channel and any other channel
- 10Mhz between channel and any harmonic peak
- 10Mhz between channel and any IMD peak
Since IMD and harmonics have far less energy than main channel frequency, so separation gap may be lower for IMD and harmonics.
But better to have 25/15/15 (channel, harmonic, IMD) separation.
For a top quality VTX and positioning pilots far from the track you can get away with values as low as 25/7/7 - this is minimum separation required for the main signal on channel frequency to be stronger than the sum of all noise on this frequency.
NOTE! Since F8 and R7 have same frequency - we always use R7 if this frequency match.
NOTE! Although all channels in the set satisfy minimum separation parameters there still are better and worse channels in every set - some channels are a bit further from IMD, harmonics and other channels than others. Our tests with indoor tinywhoop races show that with 6 pilots at 25/12/18 and 25/10/12 all channels give about the same quality - more depends on other pilot's VTX's quality than channel choice from the set.
Note that some whoops have VTX that may drift for several MHz so sometimes it is better to have more separation between main channel frequencies.
Frequency set found using algorithm by Sergey Kulakov (@klsrg).
NOTE! Lot of times there is some 5G wifi router nearby - once it starts transmitting data (somebody downloads video to phone or something) it may SEVERELY affect FPV analog video (horizontal noise lines usually) - this depends on what wifi channels router uses. Most routers allow setting channel via admin UI - channels are numbered 1 to 196 and from 120 an up they intersect with FPV frequency range. Better set lowest possible channel. To verify that it worked or simply check if there are any wifi transmitters nearby - download some wifi analyzer app to your phone (there are numerous in app store and play market).
7 pilots 26/11/11
R7 R8 F2 F4 E1 E3 B6
6 pilots 37/16/14
R1 R2 R4 R8 B6 A1
R1 R2 R8 B3 B6 A1
6 pilots 35/11/16
R1 R2 R4 R8 F7 A3
6 pilots 25/17/17
R1 R7 R8 F4 B2 A3
5 pilots 38/19/18
R2, F7, E6, B2, B4
R2, E6, B2, B4, A1
5 pilots 30/17/26
R1 R2 R8 F5 B3
4 pilots using only Raceband 37/41/36
R1, R2, R4, R5
4 pilots using only Raceband 40/34/34
R7, F6, A8, A6
7 pilots 26/11/11
R7 R8 F2 F4 E1 E3 B6
6 pilots 40/16/16
R3 R5 E2 E6 E8 B7
6 pilots 25/19/19
R2 F7 E6 E4 B4 A6
R2 E6 E4 B4 A6 A1
5 pilots 46/17/27
R1 F5 E8 B8 A8
We've used 6-pilot set R1 R2 R4 R8 B6 A1 on many endurance tinywhoop races - results wildly depend on vtx quality.
If all vtx have about the same power - video on all channels is clean with little noise, but if there is one badly
calibrated/damaged vtx with high output power - neighbor channels can be affected severely.
We've also tested 7-pilot set R7 R8 F2 F4 E1 E3 B6 briefly during training sessions - no difference from 6-pilot
set with good quality vtx.
If you have problems and have some tool to measure vtx power (ImmersionRC RFMeter for example) - try to use it. We've seen some whoop vtx output about 400-600mW when specs said it could only output 25mW! Also on some whoops like Moblite with Happymodel Diamond FC the 25mW mode outputs about 5mW and 100mW outputs about 25mw, so if particular pilot has bad video but everybody else are good - try increasing power on the problematic whoop, it may help without affecting others.
Also positioning pilots as far from the tracks is possible is IMPORTANT - min/max signal level difference from all drones should be low, otherwise vtx on other channels will affect nearby channels severely. Another tip is to remove antennas from receiver on goggles - receivers are too sensitive and with a good antenna they capture too much signal from other channels which results in video noise. Although receiver usually gets hot - it is safe to remove antennas because it doesn't transmit anything and won't burn out.
In case there is some other signal source (for example, wifi) occupying one of the channels used in the best sets - consult this chart and try to avoid such channels, although it is likely not possible for 4+ pilots.
Not supported by VTX/RX at the moment. This band was calculated to give largest possible separation using legal frequency range 5651Mhz - 5924Mhz.
8 pilots 26/11/12
5658 5684 5738 5765 5805 5832 5886 5912
Most VTX support setting custom frequency - in Betaflight VTX tab you need to add a band and uncheck Factory checkbox. When it's set to FACTORY - flight controller send band and channel index to VTX and expects VTX to have preconfigured list of channels. When set to CUSTOM (checkbox unchecked) flight controller send frequency directly.
NOTE! If band type is set to FACTORY - VTX will still use it's own preconfigured frequency despite of the one entered in Betaflight!
Some VTXs are hardware/software locked from accepting CUSTOM frequencies, but many can be unlocked using some simple procedures.
You also need to set this band to receiver in your googles. Not all receivers support custom frequencies:
ImmersionRC RapidFire - Favourites band can be set to arbitrary frequencies.
TBS Fusion - manual says that custom frequency can be set for any Favourite channel, but under firmware 1.04 the menu looks different and doesn't have such option (perhaps we were doing something wrong).
Some other receivers can be configured also, but we only list tested ones here.
Closest standard channels:
5658 - R1 (5658) +0Mhz
5684 - E2 (5685) -1Mhz
5738 - F1 (5740) -2Mhz
5765 - A6 (5765) +0Mhz
5805 - A4 (5805) +0Mhz
5832 - B6 (5828) +4Mhz
5886 - E5 (5885) +1Mhz
5912 - R8 (5917) -5Mhz
Alternatively we can use channel 8 at 5910Mhz to still fulfil separation requirements, but have it closer to standard channel.
Lowband is frequency set 5.3Ghz-5.7Ghz - completely outside normal FPV VTX range, but some VTX support it so technically it can be used, but in most countries it is completely illegal and you may cause real problems for devices that used it, so try this at your own risk or better consult local authorities for temporary usage rights.
At the moment calculator needs about 1-2 hours to get channel set for 10-12 pilots, but it seems that such sets should be possible.