The nRF24L01 transceiver module is designed to operate in the global 2.4 GHz ISM frequency band and uses GFSK modulation for data transmission. The data transfer rate can be 250kbps, 1Mbps and 2Mbps.
What is the 2.4 GHz ISM band?
The 2.4 GHz band is one of the industrial, scientific and medical (ISM) bands internationally reserved for the use of unlicensed low-power devices. Examples include cordless phones, Bluetooth devices, near-field communication (NFC) devices, and wireless computer networks (WiFi), all of which use ISM frequencies.
The second version comes with an SMA connector and a duck antenna, but that's not the real difference. The real difference is that it comes with a special RFX2401C chip that integrates PA, LNA and transmit-receive switching circuits. This range extender chip together with a duck antenna helps the module to achieve a significantly longer transmission range, about 1000m.
What is PA LNA?
PA stands for Power Amplifier. It simply increases the strength of the signal being transmitted from the nRF24L01 chip. While LNA stands for Low Noise Amplifier. The function of the LNA is to take an extremely weak and uncertain signal from the antenna (usually on the order of microvolts or below -100 dBm) and amplifies it to a more useful level (usually around 0.5 to 1V).
The low noise amplifier (LNA) of the receiving path and the power amplifier (PA) of the transmission path are connected to the antenna via a duplexer, which separates the two signals and prevents the relatively powerful PA output from overloading the sensitive LNA input.