Software Defined Radio (SDR) receiver

Version en français

We have connected a low cost Software Defined Radio receiver (SDR) to the radiotelescope antenna in order to capture radio signals from our Galaxy.

SDR Nooelec R820T2 + TCXO + SMA + box

The key NESDR SMART is the new improved version of the famous USB RTL-SDR with chipset RTL2832U and tuner R820T2, for receiving frequencies from 22 to 1700 Mhz (without gap). With such a device a computer is turned into a true wide band VHF-UHF-SHF receiver (using SDR for Windows, or linux or MacOS operating system).

SDR improvements:

  • The NESDR SMArt contains the same ultra-low phase noise 0.5PPM TCXO used in our much smaller Nano 2+ (TCXO specifications below), ensuring ultimate tuning stability in nearly any environment.
  • In the quest for lower noise, the power supply section was redesigned to implement an RF-suitable voltage regulator with under 10 µVRMS of noise. That is at least 10x lower than other designs!
  • A quality shielded inductor was used in the power supply to improve EMI rejection.
  • The included aluminum enclosure ensures stray EMI stays where it belongs–away from the sensitive RF circuitry.
  • Lower board-level temperatures further improves the SDR noise floor.

Temperature improvements:

  • A custom heatsink is affixed to the primary PCB with 3M thermal adhesive, to wick heat away from the circuit board and towards the enclosure.
  • 2 pieces of silicone thermal pad spread the rest of the heat away from the device hot spots.
  • Power consumption has been reduced by an average of 10mA, which means less heat is generated compared to other designs.
  • The result is much lower board-level temperatures–increasing stability, improving sensitivity and ensuring maximum frequency range capability. The changes were first simulated, and then field-tested with a Flir E8.

Form factor improvements:

  • The NESDR SMArt was designed to minimize annoying USB port occlusion. We re-designed the SDR from the ground up to ensure the SMArt can be used side by side in any USB-compliant device, including tightly-spaced embedded devices. There is no need to remove the enclosure to run multiple SDRs beside one another!
  • The form factor re-design allowed us to move to the more universal SMA antenna input.


  • NESDR SMArt SDR w/ brushed aluminum enclosure

SDR Specifications:

  • RTL2832U Demodulator/USB interface IC
  • R820T2 tuner IC
  • 0.5PPM, ultra-low phase noise TCXO
  • RF-suitable voltage regulator
  • Shielded primary inductor
  • Integrated custom heatsink
  • Female SMA antenna input
  • High-quality black brushed aluminum enclosure
  • Through-hole direct sampling pads on PCB

SDR TCXO Specifications:

  • Frequency stability: 0.5PPM (max)
  • Phase noise @1kHz offset: -138dBc/Hz (or better)
  • Phase noise @10kHz: -150dBc/Hz (or better)
  • Phase noise @100kHz: -152dBc/Hz (or better)

We have recently been informed of an existing preamplifier connected to the antenna dipolar source. We have powered this preamplifier by injecting 12 V DC through the coaxial cable. A second preamplifier was found necessary in front of SDR receiver in order to get a higher signal level at the SDR input. We choosed a KU LNA 133BH model.

Recently more sophisticated SDR receivers are being used simultaneously in order to get more precise measurements with a 12-14 bits analog to digital converter and a more precise frequency synchronized with an external device that is synchonized by GPS signal.

With above devices we are able to receive signals from the Galaxy. The frequency spectrum of signals received around hydrogen line frequency is obtained by a power spectrum applicationr. The energy of signals received below 1420,4 MHz corresponds to a down frequency shift due to Doppler effect related to fast escape movement of hydrogen atomes relatively to the observer. Signal with frequency received above 1420,4 MHz are coming from hydrogen sources moving toward observer.

Presently the radiotelescope is performing continuously signal measurements in atomic hydrogen band around 1420,4 MHz.

La Villette F4KLO radiotelescope WebSDR is on line. At present time, as the antenna is parked toward zenit there is no signifcant radiosource detected by the radiotelescope.

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