In FPV/ Howtos Posted by Mark Spencer Feb. 26, 2014
For decent FPV experience one is key ingredient, LRS (Long Range System) UHF system. Most if not all operate at around 433MHz frequency and RangeLink is no exception. On this page we'll try and cover some of the basic and some advance setup of RangeLink.
RangeLink UHF LRS is FPV long range radio control system working on the ISM band 431Mhz-435Mhz featuring FHSS (Frequency Hopping Spread Spectrum) method of transmitting signal.
- RSSI, buffered - Receiver's signal strength indicator in two operating modes: RF RSSI and Link Quality Indicator, which will be covered later in the text
- 12 channels PWM output
- PPM output - also called PPM-Sum or CPPM, stands for Pulse Position Modulation and if PWM is the way to drive your servos, PPM is the way to combine and carry multiple PWM signals on one line
- Dual power modes - With a flip of the switch you can choose between 200mW and 500mW output modes increasing your range in breakneck situation.
- Well filtered - Transmitter has built-in LPF (Low Pass Filter) 900-1300MHz (rejection loss over 45dB,2.4GHZ band rejection Loss over 40dB), receiver with built-in SAW band pass filter
- High sensitivity
To perform TX/RX firmware upgrade you'll need USB-to-TTL adapter of some kind, in my case that is prolific PL2303, but most of them will work. Plug it into the computer and make sure correct drivers are installed.
You'll also need software and set of firmware which at the moment of writing is version v1.24 for RX and v1.27 for TX and can be found at the link supplied by manufacturer of the RangeLink, here.
Receiving end of adapter is logically connected transmitting end of the RangeLink TX/RX, and vice versa.
Take a note of the pin-out, in this case:
- blue wire is RX (the wire trough which adapter is going to receive data from RangeLink TX/RX)
- white wire TX (the wire trough which adapter is going to send data to RangeLink TX/RX)
- black wire is ground
First, lets flash the RangeLink transmitter. With the info above this is how connection should look like, port TTL232 on the left.
Power the TX, connect the USB-to-TTL adapter to the PC and then to the RangeLink transmitter. Run flashlinkprj.exe found in the zip file downloaded from the location above.
Select the COM port of the prolific adapter, in my case it's COM3. By clicking "Get Info" you'll get the installed version of the TX firmware and at the same time verify that everything is connected properly and your computer is communicating with the transmitter.
If everything went OK, click on the "Open", select the .hex file downloaded from the link above and be sure to select the one with "tx" in its name. Now click "Send" and wait for the process to finish.
Disconnect from the computer and power down the TX.
RangeLink RX flashing procedure is similar. Last row of the pins on the RangeLink receiver for serial communication is marked as RX/TX/GND and should be connected with the USB-to-TTL adapter the same way we did with the RangeLink TX.
RangeLink receiver could be powered with ESC.
Power the RX, connect the USB-to-TTL adapter to the PC and then to the RangeLink RX. Run flashlinkprj.exe.
Select the COM port of the prolific adapter. By clicking "Get Info" you'll get the installed version of the RX firmware and at the same time verify that everything is connected properly and your computer is communicating with the receiver.
If everything went OK, click on the "Open", select the .hex file downloaded from the link above and be sure to select the one with "rx" in its name. Now click "Send" and wait for the process to finish.
Disconnect USB-to-TTL from the receiver and power it down.
RangeLink is offering two selectable modes of RSSI: RF RSSI and Link Quality Indicator.
In Rf terms it tells you how strongly the Rf signal itself is received by the Rx. The Rf RSSI will vary quite a lot during normal flight depending on range, antenna orientation, blockage, and so forth and if scaled into a percentage, you might expect to still be able to receive 100% of the packets (full smooth control) with RSSI as low as 30%. Mean Rf RSSI value is useful for giving you some sense of range as it'll go down the further away you go, even if the Rx is still receiving 100% of the packets.
When the output it switched to link quality indicator it tells you (via the same analog voltage range) only the % packets received. That means it may show 100% almost all the time, until you drop below that low Rf RSSI threshold and then link quality tends to drop fairly quickly as it starts losing packets. It is *roughly* equivalent to looking at the blinking light. When it's blinking steadily, then link quality would also be 100%. If it stutters then it'll be less than 100%, and when it stops, it'll be 0%.