Frequency Penetration

We’ve got to the point in planning when we need to figure out what video system will we want to use for our FPV 250 Racer. There are lots of misconceptions out there, but there is one big truth: “The lower the frequency, the better the penetration is.” There are several frequencies available for FPV use, and you will need to figure out which one you will be using for your racing or any other type of drone. Let’s see some pointers to make your decision easier. Look at the below diagram to understand how the frequencies work.

penetrationLet's look at the image on the right. As you can see your aircraft is behind a few trees or bushes. The lower frequency FPV system will allow better penetration, so the signal coming back to the pilot will seem stronger and the pilot will notice less breakups an interferences.

Using a higher frequency FPV system (5.8Ghz) even at the same power level as the lower frequency counterpart, will have less penetration power, and because of that as soon as you lose visual line of sight, (being behind bushes, trees etc.) you will experience high level of image breakup, dropouts and interference lines.

In most environments FPV flying drones, airplanes or any other multi-rotor helicopters will need to be done within a visual line of sight (LOS from here on). In most club and model association environments the FPV pilot will need to have a dedicated “spotter” which will follow the aircraft visually while the pilot is flying it. This requirement is a safety measure to allow the “spotter” to save the aircraft in case of a video system failure, in case somebody else behind plugs in an FPV transmitter while you are in mid flight, etc.

In the Drone Racing environment the power level of the video transmitters are usually standardized between the racers. The racing environment all racers will be using the same power level to give equal chances the all pilots. Usually during these races the spotter is not there to take over control, but to count the laps, missed gates or watch out for the performance of the pilot. Each pilot should have a spotter here as well which can relay information on how others are doing, if there is any communication from the racing judges, etc. These races are usually done within LOS, in stadiums, domes, etc. Some others are organizing races in woods, forests, parks where the constant flickering image from interference makes it much more challenging to compete.

So let’s go back to the frequency selection for a second. One point of decision on which frequency to use should be the antenna selection. One should know that the lower the frequency, the bigger the antennas are. This is usually not a problem on the receiver side where you can add as big antenna as you wish, but on the transmitter which is on the drone it really matter how big your antenna is.

For reference let’s see some numbers:

So based on the above information the frequency selection should be easy. If you have the real esate on the bird to use lower frequencies, go with it, if not, your choice is clearly 5.8Ghz. Please note use of 2.4Ghz should be avoided as much as possible because almost all RC transmitters work on 2.4Ghz which will render the video useless on this frequency.