Q4: What frequency should I use for my FPV system and why?
Beyond the arguments and opinions available on the forums, there are some basic rules that you should apply. The most important is that you should NOT use the same frequency for video as you use for RC control. Even if it appears successful for ground testing, you will introduce noise in the video from the RC controller transmissions, and you could lose RC control of your plane once you start flying. Always use a different frequency. Also, regardless of the frequency used, itís important to have as much distance as possible between your video transmitter and your RC receiver, and ALWAYS perform a range check both before the video equipment is on and after to make sure your RC range hasnít been significantly affected.
If you are using 2.4GHz for RC control, itís important to note that you should be using a full range receiver and not a park flyer receiver. For Spektrum, you should be using an AR7000 or higher model. If you are in an area where there will not be interference from 2.4GHz sources such as RC radios, Wifi, or other similar wireless equipment, then often 2.4GHz offers the best picture quality and excellent performance. Most people donít live in this type of area, so other frequencies may be useful. Hereís a summary of my opinions regarding the various frequencies available:
900MHz: Can offer some of the best range. A wide selection of antennas are available and in most areas it does not have much outside interference. Can penetrate obstacles such as trees and walls better than higher frequencies (but you still should maintain line-of-sight when flying). It may not be legal in some countries, and is restricted to one channel (910MHz) in the US. Some of the antennas can be large because of the wavelength at this frequency. It can cause some servos to jitter due to improper filtering in the servo.
1.2-1.3GHz (1200-1300MHz): Offers excellent range and also seems to be mostly clear of interference in the US and in other countries. Can penetrate obstacles such as trees and walls better than higher frequencies (but you still should maintain line-of-sight when flying). It may not be legal in some countries, and is restricted to one channel (1280MHz) in the US. This is personally my favorite frequency here in the US.
2.4GHz: Offers excellent video quality and sometimes stereo audio depending on the equipment. In areas without interference, 2.4GHz can work amazingly well and is the favorite of many. Although it will penetrate some obstacles, it is absorbed more than some of the lower frequencies and care should be taken to avoid flying behind obstacles. It may receive interference from the abundance of 2.4GHz devices available, and cannot be used with 2.4GHz RC Systems. Some goggles have built in 2.4GHz receivers, which can make an amazingly portable FPV system.
5.8GHz: Has the benefit of using newer technology in the RF module designs similar to 2.4GHz, but there is almost no interference on this frequency band. Very clear video and often stereo audio is included. Will not have the same range given the same power output, but still can be good for flying longer distances with the proper antennas. Will not penetrate obstacles well and the video may go away abruptly if you fly behind a tree. Also seems to be more sensitive to multipath interference in some situations. Some goggles have built in 5.8GHz receivers, which can make an amazingly portable FPV system.