Here are some steps to help you troubleshoot R9M module and receiver for poor performance and range issues. If you followed my R9M Setup guide previously, you probably would have avoided many issues, but in case you didn’t I hope this guide is useful too.
Table of Content
- Firmware Updates
- Get Better Antennas
- Antenna Mounting
- Turning Off Internal Module
- Check Receiver
- No Softserial for FPort
- Increase Power
- RF Noisy Environment
Update your R9M module and R9MM receiver to the latest version for bug fixes and reliability improvement.
Using the Correct Frequency
The R9M is advertised as a 900MHz long range RC system, but in fact it operates on two nearby frequencies. To be specific, they are 868MHz and 915MHz.
For EU countries, you should be using 868MHz, anyone else should be using 915MHz. Anyway don’t take my words for it, double check which frequency you should be using in your region to avoid interference.
Why is this a problem? Well, if you use 868MHz in the US, or if you use 915MHz in the EU, will leave you open to all sorts of interference from other radio systems like cell networks.
With the “Flex” firmware (requires OpenTX 2.2.3 or newer), you can easily switch frequency in the model setup menu. With the normal firmware, you would have to flash both your R9M module and R9MM receiver to either the EU-LBT firmware or FCC firmware in order to use different frequencies.
Get Better Antennas
If you are using a stock antennas, try get something better. It’s known that the stock antennas are out of tuned. Also make sure the RX antennas are made for the frequency you use.
- TX Antenna, Super 8 (868-915MHz): Banggood | HorusRC | Amazon
- TX Antenna, Diamond (868-915MHz): RMRC | GetFPV| Amazon
- RX Antenna, 915MHz: Banggood | HorusRC
RX Antenna, 868MHz: Banggood
Mounting Antenna Correctly
Consider the position and orientation of your TX and RX antennas, try re-positioning to optimize reception. Check if the SMA connector is snug on the R9M module, make sure Antenna is not damaged or deformed.
Turning Off Internal TX Module
Make sure you have turned off the internal 2.4GHz TX module, as it can interfere with the 900MHz system and use up your battery.
Your receiver can get damaged easily in a crash if it wasn’t protected well inside the quad.
Check all solder joints and connectors, re-do your soldering if necessary.
Check if the IPEX connector of the RX antennas are loose, which can cause intermittent signal loss. Make sure the coax cable has no sign of physical damage, damaged shield can affect your range. Inspect carefully the exposed core of a coax cable, and make sure it’s not been cut by accident, as a change in length can reduce performance. (effectively changing the antenna tune)
The active element will need to be the same length as the passive element, which for the Crossfire at 915Mhz is 78mm. For those of you operating at 868Mhz the length is 82mm.
Check receiver PCB closely for damage, for example, missing surface mount components, damaged copper traces etc.
You should not use SoftSerial for F.Port RC control link because Softserial is too slow. Try using a normal UART for FPort, or flash non-F.Port to use SBUS and see if you can fix the problem.
Have you tried increasing the output power of your R9M module? You can do this in the model setup menu, scroll down to External Module. But in theory, 100mW should give you a couple of miles easily.
RF Noisy Environment?
Check with other flyers with 900MHz system in that spot, see if they have the same problem. Or simply try to fly in a different location. There could be transmission towers or other RF emitting equipment nearby that you are unaware of, and these can affect your range.
Make sure there is no obstacles between you and your aircraft during flight.