WA3TFS SDR Upverter Design

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WA3TFS Upverter P1874-720px.jpg

Features

SDR up-converter/receiver shifts HF (0-30 MHz) frequencies up by 100 MHz. Used to listen to HF frequencies on an inexpensive RTL-SDR module.

Schematic

WA3TFS Upverter Schematic.PNG

Pass Filter

  • 9 turns on FT37-2 = 0.3 uH

WA3TFS Upverter Inductor.PNG

  • LTSpice Simulation
    • 1-100 MHz

WA3TFS Upverter Pass Filter.PNG

  • LTSpice Simulation
    • 1MHz-1GHz

WA3TFS Upverter Pass Filter 1MHz-to-1GHz.PNG

Software

Build

  • Nice silver mica caps for the band pass filter
    • My kit was missing the center cap of the band pass filter (150 pF)
    • I used a junk box ceramic disc cap
  • 30pF cap installed in J_A to J_B marked 300
  • Build was too tough due to very small pads on the PCB
    • Particularly tough to solder ground pads
    • Pad shapes were not round so less area to set soldering iron
  • Is LO drive more than 7 dBm?
  • Pin 1 orientations on the mixer and oscillator "backwards" from other board legends
    • Pin 1 shown in red circle

WA3TFS Upverter pcb r11.jpg

RTL-SDR

  • RTL-SDR DONGLES (RTL2832U) - rtl-sdr.com site
  • <1 PPM temperature compensated oscillator (TCXO)
    • Accurate tuning and almost zero temperature drift (2 PPM max. initial offset, 0.5-1 PPM temperature drift)
    • SMA female antenna port
    • Generic dongles use the less common MCX or PAL antenna ports
    • SMA is more common, so more adapters and antennas are available for it
    • It is also more durable and has lower RF insertion losses
  • 4.5V USB powered bias tee
    • This allows the RTL-SDR to power low noise amplifiers (like the LNA4ALL, HABAMP, RTL-SDR Blog ADS-B LNA) and active antennas through the coax cable
    • Can be enabled in software (see V3 users guide).
  • HF Direct Sampling Mode
    • Listen to 500 kHz - 24 MHz with direct sampling
    • Simply connect an HF antenna to the SMA port, and choose the Q-branch mode
    • There is a built in 25 MHz low pass filter, but additional HF filters may be required for optimal performance (e.g. to attenuate strong MW AM).
  • Aluminium case and passive cooling
    • These units come stock with an aluminum case and passive cooling via a silicon thermal pad
    • This stops reception failing due to heat when used above ~1.2 GHz
  • Improved Antennas
    • We provide an excellent dipole antenna starter kit for newbies
    • Use the included mounts and extension cable to mount the dipole in good position for optimal reception
    • Receives terrestrial and VHF satellite signals
  • Various additional improvements compared to other RTL-SDRs
    • R820T2 tuner, higher quality passive components, a choke on the USB line to reduce USB noise, a much improved PCB design for significantly less internal spurs and noise, various break-out pads, improved ESD protection, additional bypass capacitors and ferrite power line chokes, improved front end matching circuit, a modified power design for improved long term reliability, and a better LDO.

RTL-SDR improvements v3new800x800.jpg

Wiring

  • SPDT switch
    • One switch pole powers the card (turns off 12V)
    • Other switch pole switched in/out the Upverter
    • Could just move the cable

WA3TFS Upverter Wiring.PNG

Enclosure

WA3TFS Upverter P1878-720px.jpg

WA3TFS Upverter P1880-720px.jpg

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