There are more than 40 channels on a video transmitter (VTX) you can choose from, sometimes even up to 72. It can be confusing for a beginner as which channel is best to use. The decision comes down to whether you fly alone, or with other people.
Best VTX Channel for Flying Alone
If you fly solo, you can basically use any channel you want, as long as it’s legal in the part of the world you are flying. However there are some tricks in selecting the best channel.
First of all, some channels output more power than others. You can find out with special equipment, like the ImmersionRC RF Power Meter. I always test output power of the VTX in my reviews so you might be able to find the answer there.
However, just based on my experience, lower frequency channels usually have higher output power. For example on Raceband, R1 usually has higher output power than R8.
Another thing to take into account is the tuning of your antennas. Assuming they are both tuned to 5800MHz, then the performance is going to be better on channel F4 (Fatshark 4) or R5 (Raceband 5). If they are tuned to 5700MHz, then the best channels would be E1 or R2.
It’s hard to know the exact tuning of an antenna, unless you have the equipment to test them, so really I wouldn’t worry about that too much. If you have time, test all the channels and find the one that works the best for you. Otherwise just pick the first channel in a band, like R1 or F1 which is easy to access and remember :)
Best FPV Channel for Flying in a Group
If you often fly with other people, then you have to choose your channels carefully. Between channels, there should be adequate separation to avoid interference. Also there are IMD frequencies you want to avoid using too. I will explain what IMD is later.
Taking into account the frequency spacing and IMD, the best FPV channels are the following, which allows up to 6 pilots flying at the same time:
- 5645 (E4)
- 5685 (E2)
- 5760 (F2)
- 5805 (A4)
- 5905 (E6)
- 5945 (E8)
Beware that not all of these frequencies may be legal where you fly. Check your local regulations before using.
For places that are limited to frequencies between 5725MHz – 5866MHz due to regulation, you can use these channels instead, however because the range is smaller, only 4 pilots can fly at the same time:
- 5732 (R3)
- 5769 (R4)
- 5828 (B6)
- 5865 (A1)
The selection of these frequencies is based on the assumption that everyone is using a decent VTX and doesn’t bleed into other channels.
FPV Channel Management
When flying with a group, the first thing you should do when you arrive is to ask what frequency everyone is using, so you know what channels are free to use. Pick a channel that is as far away as possible from the occupied channels following the above selecting to minimize interference.
Also make sure everyone sets the output power to 200mW or lower. If you are flying indoor, this has to be 25mW or lower.
It would also help if one person is using RHCP antennas, and the neighbouring pilots uses LHCP. This is because opposite polarisation will result in as much as 20dB signal reduction, reducing interference between pilots. We discussed how dB can be related to FPV range in this post.
When choosing FPV antennas, pay attention to Axial Ratio. It’s a measurement of how good an antenna can reject opposite polarized antenna signal. This property is not only important for flying with others, it’s also useful for rejecting multi-path interference, because a bounced signal has reversed polarity.
We have an article on how to manage channels and VTX when flying as a group, it’s a bit old but some of the advice is still valid.
What’s IMD Frequency?
IMD stands for inter-modulation distortion, it basically means that two different frequencies can form a harmonic frequency.
For example, if we have one pilot using F2 (5760MHz), a second pilot using F4 (5800MHz), and a third pilot using F6 (5840MHz), although these frequencies have good enough separation at 40MHz, Pilot 3 might still get interference because of IMD. F2 and F4 together can form a harmonic signal that appears on F6. Although this harmonics signal is weaker, it could be enough to cause interference to the 3rd pilot who is on F6.
You can calculate the IMD frequency with this equation: F1 x 2 – F2 (5760×2-5800=5720)
And you will get a second value by swapping F1 and F2: F2 x 2 – F1 (5800×2-5760=5840)
See? 5840 is exactly F6.