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.

One comment

  1. Induhvidual

    If only there was a cheap development board using a RFFC5072, or RFFC5071, on it (For say around £25.99 – since it would replace both the ADL5350 and the ADF4350 development boards). And could provide coverage up to 6GHz instead of just down-converting 2.4GHz to 1.4GHz.

    The RFFC5072 is one for the mixers used in a HackRF: a 85 – 4200 MHz Wideband Synthesizer / VCO with Integrated 30MHz 6000 MHz RF Mixer. And in the comments for the Outernet moRFeus ( https://www.rtl-sdr.com/morfeus-a-low-cost-wideband-signal-generator-and-frequency-mixer/ ) it also appears to also use the same chip (FC5072A) with a cheap (EFM8) 8-bit MCU to control it over SPI, detect button presses through the GPIO ports, provide the USB port and drive a LCD display.

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