RF Noise Generator

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NoiseGen-P783-720px.jpg

Design

  • Useful as a filter test signal source
    • Pass filters
    • Crystal filters
  • From Experimental Methods in RF Design
    • Fig 7.72
    • Described as "not flat"
  • "Junk box" parts
    • (2) 2N3904 transistors
    • (2) 5V (nominal) zener diodes
  • Noise figure -50 dBm @ 10 MHz

Schematic

Ng-sch-prototype.PNG

Prototype

  • Unique nodes in red
  • Prototype on single sided copper clad PCB
  • KiCAD zener packages have backwards silkscreen (will need to fix on OshPark PCBs)

NG-layout.PNG

Meaurements

  • 12V, 43mA current draw
  • Rigol DS1054Z
    • 50 MHz scope with mods
    • UltraScope settings
      • SCAL 1.00 V
      • H 200nS
    • FFT settings
      • CF = 16 MHz
      • 2 MHz start, 50 MHz stop
  • RBW 416.6 KHz
  • Background noise
  • Generator off
  • Average ~ -64 dB

NG OFF.PNG

  • Noise Generator On
  • Falls off with frequency, but better than -50 dB

NG ON.PNG

  • Measured performance per EMiRFD (predicted - 50 dB)

High Pass Filter

  • Output series coupling 10 nF cap and 50 Ohm Load resistor make a High Pass Filter at 312 KHz
  • No real point in making a better filter, but why not?

Design Inputs

Filter DesignInputs.PNG

Schematic - 5% Standard parts

Filter DesignSchematic.PNG

Predicted Response

Filter DesignGain.PNG

Toroid winding

  • T37 cores, approx .5" per turn, plus tails

Toroid-6.8uH.PNG

Toroid-3.9uH.PNG

High Pass Performance

InputToHighPassFilter.PNG

OutoutFromHighPassFilter.PNG

Build / Enclosure

  • Used very old, but high quality chassis mount BNC connector
    • Silver connector has a nice patina
  • Built onto Single Side PCB material
    • Acts as ground plane
    • Pads cut from PCB material and superglued down onto the Base PCB
  • Hot glued down into plastic enclosure

NoiseGen-P783-720px.jpg

NoiseGen-P790-720px.jpg

NoiseGen-P787-720px.jpg

Assembly Sheet

RF Noise Generator Rev 1