All ExpressLRS transmitters and receivers work on the certain frequency. Both devices must operate on the exact frequency in order to be able to talk to each other. The precision of the frequency is mostly dependable on the crystal oscillator (XO). This makes crystal oscillator the very important part in the ELRS hardware.
One of the most notorious problems with ExpressLRS hardware is that some manufacturers hardware have unacceptable high frequency error. And in the high or low temperatures it gets even worse. There is certain threshold of the frequency error for the link to work. Up to
40 ppm error (=~ 100 kHz) frequency difference is considered still acceptable.
Detailed explanation about the Crystal Oscillator (XO) Frequency Error can be found on the
expresslrs.org webpage: https://www.expresslrs.org/3.0/hardware/crystal-frequency-error/
BetaFPV SuperD receiver
BetaFPV SuperD receiver is the first ExpressLRS receiver with full dual diversity and temperature compensated crystal. Receiver has two SX1280 LoRa RF ICs, two PA/LNA amplifiers and two antenna connectors. Power amplifier provides 100mW for telemetry link.
Specifications Item: BETAFPV SuperD ELRS 2.4G Diversity Receiver MCU: ESP32 PICO D4, dual SX1280 (SX1281) Antenna Connector: IPEX MHF 1/U.FL RF Frequency: 2.4GHz (2400~2480MHz) Telemetry Power: 20dBm ( 100mW) Receiver Protocol: CRSF Input Voltage: +5V DC @ “+” pad PCB Size: 22mm*14mm Weight: 1.1g excluding antenna Crystal oscillator: high-quality TCXO
Happymodel TCXO EP1,EP2 and EP1 Dual receivers
Happymodel has also released their three EP1, EP2 and EP1 Dual ExpressLRS receivers with temperature compensated crystals (TCXO).
EP1 TCXO Receiver Type: ISM2.4GHz ESP8285 MCU SX1280(SX1281)IMLTRT RF Module Omni directional antenna Frequency Range: 2400 MHz to 2500 MHz Receive refresh rate: 25HZ~500Hz Working voltage: 5V Weight: 0.41g (without antenna) Dimension: 10mm*10mm*6mm Peak gain: 2.23dB Default Firmware out of factory: HappyModel_EP_2400_RX V2.2 version Built-in a TCXO (temperature compensated crystal oscillator)
EP2 TCXO Receiver Type: ISM2.4GHz ESP8285 MCU SX1280(SX1281)IMLTRT RF Module SMD Ceramic antenna Frequency Range: 2400 MHz to 2500 MHz Receive refresh rate: 25HZ~500Hz Working voltage: 5v Weight: 0.44g Dimension: 10mm*10mm*6mm Peak gain: 3.7dB Default Firmware out of factory: HappyModel_EP_2400_RX V2.2 version Built-in a TCXO (temperature compensated crystal oscillator)
EP1 Dual TCXO Receiver Type: ISM2.4GHz ESP32 PICO D4, dual SX1280(SX1281) Antenna connector: IPEX MHF 1/U.FL RF Frequency: 2.4GHz (2400~2480MHz) Telemetry power: >19dbm Receiver protocol: CRSF Input voltage: +5V DC @ “+” pad PCB size: 19mm x 14mm Weight: 1g (excluding antenna) Built-in a TCXO (temperature compensated crystal oscillator) Firmware: HappyModel EP1 Dual 2400 RX (starting from ExpressLRS V3.0)
Both manufacturers dual diversity receivers have multicolored LED for status indication.
SuperD and EP1 Dual receiver RGB status indication is shown below.
RGB Color Status Description Rainbow Fade effect Power on Green Quick flash WIFI upgrading mode Red Quick flash No RF chip detected Orange Double flash Binding mode Orange Triple flash Connected, but mismatched model-match configuration Orange Slow flash Waiting for connection Solid on Connected and color indicates packet rate (see below)
The RGB light color corresponding to the packet rate