Monday, May 26, 2014

RTL SDR Upconverter for T820 Series

Realtek RTL2832U DVB-T dongles can be used as a cheap SDR. As a DAB/DAB+/FM demodulator it’s possible to fetch 8-bit I/Q-samples from RTL. Moderate low loss sampling rate of 2.56 MS/s is suggested even the device can support upto 3.2 MS/s. For more information check official page of rtl-sdr.

To listen HF !!!

As per the specification of Rafael Micro R820T its frequency range is 24 - 1766 MHz which can vary due to multiple reasons. Here I am describing a simplest up-converter circuit to listen HF in rtl sdr. The IF chosen is 24 MHz just because 24MHz resonator is easily available from old computers. The circuit uses well known mixer NE 602 with unturned input and output mode.

The circuit uses a 24MHz ceramic resonator as oscillator for heterodyning with the input RF signal to generate IF+/-RF signal which falls in the rtl's operating freq range and can be demodulated by the rtl sdr. The power supply for the circuit is taken from USB as shown.


With a surface mount MCX plug the whole circuit can be build on general purpose pcb. The DPDT switch allows to switch b/w the up-converter bypass and through up-converter. The only disadvantage I noticed is the harmonics in every 24n ( n ={1,2,3,..n}  instances in the frequency spectrum, the gap between such harmonic instances can be rectified by using higher frequency oscillator like 100MHz.

My Prototype


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