Over on YouTube Adam Alicajic, seller of the LNA4ALL low noise amplifier has uploaded a video showing how to create a simple downconverter using a 1.3 GHz local oscillator and an LNA4ALL. A downconverter extends the frequency range of the RTL-SDR to frequencies higher than the RTL-SDR’s 1.7 GHz limit.
Adam capacitively connects the 1.3 GHz local oscillator to the input of the LNA4ALL, which causes the input signal to be mixed with the input signal from the antenna. This moves a test 2.8 GHz signal down to 1.5 GHz, which is receivable by the RTL-SDR.
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.
Over on YouTube Adam Alicajic has uploaded two videos which show an experiment where he successfully receives a test 24 GHz carrier signal with an RTL-SDR dongle.
In the first video he uses mixer setup to convert the 24 GHz signal down to 432 MHz, which is within the tunable range of the RTL-SDR. In the second video he uses a salvaged downconverter unit from some sort of communications device to do the same.