In this article, we will look into the concepts of radio transmission and check the FrSky Range Test. The range of a radio system is one of the most underlying quantities we check while purchasing a new radio. If the reviews mention bad range, we would usually stay away from those radio systems. This is also applicable to video transmitters as well. For a good RC link, it is important to have a good range from the transmitter to the receiver. 

What is RF?


RF or Radio Frequency refers to the use of electromagnetic radiation for transferring information between two circuits that have no direct electrical connection. In layman’s terms, RF is what gives electronic systems to communicate with each other without any direct contact or wiring between them.

In RC, the term RC refers to Radio Control, so as you might have guessed, the radio in it refers to Radio Frequency or RF. This is what allows your transmitter radio to communicate with your receiver on your drone or craft wirelessly over a large distance.



Why do I need to care about the RF performance of my radio?


Two reasons - Range and stability. Unless you want to fly your drone only in your backyard (even that would require basic RF performance), you will need a good quality RF link.

The range of the system is highly dependent on your environment, the frequency used for transmission, interferences, and most importantly -  the RF output power. In most transmitters, the maximum output RF power is 100mW. On a 2.4GHz link, this is enough for a few miles of range in a line of sight situation with no interferences. But the thing about frequency is that the lower the frequency, the longer-range you get. This is because, the lower the frequency, the longer the wavelength of the RF signal, and the longer the wavelength, the more distance the RF signal can propagate. This is why the FrSky R9M system uses 900Mhz as it will give more penetration and range than a traditional 2.4Ghz system at the same power output.


But there is a trade-off for using lower frequency longer wavelength, the lesser the data that can be transmitted reliably as it has less bandwidth for transmission and is more prone to interferences from nearby devices operating under the same frequency. In a normal RC link, the data transmitted is quite low, a few KiloBytes per second. But on an FPV system, the data transmitted is much higher and requires more bandwidth -  which is why most FPV systems operate at 5.8GHz. Although there are FPV systems that operate in the 2.4 and 1.3GHz band for longer range; these systems cannot be used by more than 2 or 3 pilots simultaneously in the same area.



Sounds important. What can I do to check my FrSky Range Test? 


All FrSky internal XJT modules have an RF output power of 100mW fixed. To check the actual performance of the RC link you will need to do a range test on your transmitter and receiver.


  • Go to the ‘SETUP’ page on your transmitter
  • Scroll to find ‘Internal RF’ (or ‘External RF’ in case you are using an external module such as the R9M)
  • Select the ‘[Rng]’ option.


This will set your transmitter into a very low power output state (0.1mW). You will now need to move your receiver away from the transmitter while keeping an eye on the RSSI value shows.

Your receiver should fail-safe after a few meters. In case it fail-safes at very short distances like 1 or 2m, it means you have a faulty receiver or transmitter module; check the antenna connection well.

On external modules like the R9M, the maximum output power is actually 1W! This, coupled with the fact that it is a 900MHz system, would give you an extremely long distance. I have seen people go 20KM+ on it!


How can I keep my RF performance on its top game?


There are a few things you should do right if you want the best range and RF performance out of your radios.

  1. Make sure your antennas are plugged in rightly on your receivers.
  2. Make sure the antenna is placed away from materials like Carbon Fiber and other reflective surfaces
  3. If your antenna’s active element is damaged, replace the antenna ASAP.
  4. Never keep the transmitter and receivers right next to each other.
  5. Try to be free of Electro Static Discharge while working with your transmitter modules and receivers as these discharges can easily kill the sensitive RF components on the transmitter and receiver.


In this article, we have seen what Radio Frequency is and how it affects your RC link. We have dived a bit into the theory of RF systems and how should you take care of your equipment for peak performance. We have also seen how to check the range and FrSky Range Test for your radio.