Realtek RTL2832/Elonics E4000 SDR Experiments

Overview

It has recently been discovered that a Realtek RTL2832-based Digital Video Broadcast - Terrestrial (DVB-T) tuner can be adapted into a low-cost Software Defined Radio (SDR).

The Realtek RTL2832 quadrature COFDM demodulator is usually combined with an Elonics E4000 multi-band RF tuner.  The front-end E4000 tuner contains the actual RF section.  This little 33-pin chip provides a low-noise amplifier, programmable RF tracking filter, quadrature mixer, PLL frequency synthesizer & VCO, DC offset removal, and final IF filtering and amplification.  Experimention has shown the abilty to tune between 54 - 1110 MHz and 1260 - 2200 MHz.  Performance suffers a bit below 64 MHz and above 1700 MHz.  Note that it is possible to "directly sample" signals below 30 MHz by injecting them directly into pin 1 of the Realtek RTL2832.

The PLL synthesizer uses a 28.8 MHz crystal for the reference frequency standard.  The stock crystal doesn't offer the best performance, as these tuners are consumer devices and were meant for receiving wideband signals.  Replacing the 28.8 MHz crystal with a more stable reference source will prevent any frequency drift, which is noticable when receiving narrowband signals.

The E4000 tuner utilizes a direct conversion "zero IF" architechture.  This means the Local Oscillator (LO) is set the same frequency as the signal you wish to receive.  The outputs from the quadrature RF mixer are an analog In-Phase (I - 0°) and a Quadrature-Phase (Q - 90°) baseband signal.  The I/Q baseband signals are then passed onto the RTL2832 for further processing and to do the actual signal demodulation.  The maximum sample rate is around 3.2 million samples per second (MS/s) but using a slightly slow sampler rate (1.0 - 2.8 MS/s) will prevent the demodulation process from dropping samples.

Various free software packages such as GNU Radio or HDSDR are available to "tune" the Elonics E4000 / Realtek RTL2832 combination to the frequency and demodulation setting you choose.  The RTL2832 also contains a standard USB interface, which is how the device is programmed and data sent back to your computer.  The software, especially under Linux, is still a bit tricky to understand, but there are numerous sources on the Internet to go for additional help.


Elonics E4000 Block Diagram

Pictures & Construction Notes

Overview of a generic Realtek RTL2832U / Elonics E4000-based DVB-T USB tuner stick.

These tuners are all over eBay for under $30.

There is no manufacture data or documentation available.  The label on the PC board's upper-left says: DB-1AD Ver:1.1

Closeup of the RF input to the Elonics E4000.

There is a back-to-back diode protector on the RF input to clamp any voltage spikes.  When using an external antenna, the diode should be left on the board, but for Intermediate Frequency (IF) or high-UHF/microwave applications, you may want to remove this diode.  Just be careful about static electricity on the RF input.

Alternate view.

RF input in on the top, then the Elonics E4000 and Realtek RTL2832U.

A 28.8 MHz crystal is to the left of the Elonics E4000.

The black rectangle just below the Realtek RTL2832U is an IR sensor for a remote control.

The LED is for power indication and a 3.3 VDC voltage regulator is on the lower-right.

The USB jack is along the bottom.

Bottom view.

Antenna input is on the top.

The stock PAL antenna connector was removed on the RF input and a salvaged SMB connector was added.

This will allow for easy removal of the RF input while still maintaining the proper impedance.

A small coaxial pigtail will also work, for more permanent installations.

Two threaded #6 posts were added to the tuner's circuit board to allow for "stand-off" mounting.

Mounting the receiver circuit board in an old keyboard switch case.

An USB extender cable was salvaged to allow the tuner to be easily disconnected.

The USB input from the computer is via a shielded 4-pin microphone jack.  This is a bit of overkill, but shielded USB jacks are hard to find.

A high-quality panel-mount BNC jack is used for the RF input.

Alternate view.

The incoming USB +5 VDC power line (red) has a series 10 µH inductor and a shunt 33 µF capacitor added to it.

Ferrite beads where also slipped over the USB's "Data +" (green) and "Data -" (white) wires.

Switching power supplies and radio receivers don't mix...  For maximum low-spurious response from the tuner, an external linear +5 VDC power source should be used.

A linear "wall wart-type" power supply and 78L05 voltage regulator should be fine.

Closeup of the salvaged 4-pin microphone connector turned into a nice shielded USB connection.

Be sure to carefully watch your pins if you make this type connection.