Tagged: 2.4 GHz

A Low Cost 2.4 GHz Downconverter from off the Shelf Dev Boards

Over on GitHub Ian Wraith has released his design and microcontroller code for a low cost 2.4 GHz downconverter circuit. A downconverter is a hardware device that shifts the signals that it receives into a lower frequency band. This is useful in the case of RTL-SDRs and Airspy SDRs, as their maximum frequency range is only 1.7 GHz. Ian's 2.4 GHz downconverter reduces those 2.4 GHz signals down to 1 GHz, which can then be received with his Airspy.

Rather than designing a circuit from scratch, Ian's design makes use of several very cheap Chinese evaluation/development boards that he found on eBay. It costs of a mixer board, oscillator board, and an STM32 development board for controlling the oscillator board via SPI. The whole set of hardware cost him less than £30 (~37 USD).

After spending some time working through the difficulties in programming the SPI interface on the STM32 board, he was able to get the downconverter circuit fully working. He notes that he's been able to receive WiFi, Zigbee, Bluetooth and ISM band signals at 2.4 GHz, as well as 3G and 4G cellular signals at 2.6 GHz.

Ian Wraith's Downconverter consisting of three off the shelf cheap Chinese eBay boards.
Ian Wraith's Downconverter consisting of three off the shelf cheap Chinese eBay boards.

Sniffing and Decoding NRF24L01+ and Bluetooth LE Packets with the RTL-SDR

Omri Iluz wrote in to us to let us know about his recent project which involves sniffing and decoding wireless packets at 2.4 GHz from NRF24L01+ and Bluetooth Low Energy (BTLE) transceivers. The NRF24L01+ is a popular wireless transceiver which is used in many common devices such as keyboards, mice, remote controls, toys and appliances.

Since 2.4 GHz is out of any of the RTL-SDR’s receivable range, Omri used a cheap downconverter which he was able to buy from China using Aliexpress. The downconverter converts the 2.4 GHz signal into a lower frequency at around 400 MHz which is in the receivable range of the RTL-SDR.

He was then able to use his NRF24-BTLE-Decoder software that he developed to convert the received data from the NRF24L01+ transceiver into a decoded packet by simply piping the output of RTL_FM into his program.

Since the NRF24L01+ uses hardware similar to the Bluetooth Low Energy (BTLE) protocol, Omri was able to modify his code to be able to also decode BTLE packets.

2.4GHz NRF24 packet received on the RTL-SDR from a Logitech mouse using a downconverter
2.4GHz packet received on the RTL-SDR + downconverter from a Logitech mouse
decodednrf
Decoded NRF24 Packets