RF Noise Generator

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NoiseGen-P783-720px.jpg

Design[edit]

  • 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[edit]

Ng-sch-prototype.PNG

Prototype[edit]

  • 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[edit]

  • 12V, 43mA current draw

tinySA Measurements[edit]

  • 1-30 MHz
  • Power Off

NoiseGenOnTinySA Off.PNG

  • Power On

NoiseGenOnTinySA On.PNG

  • 100 KHz-1 MHz
  • Power Off

NoiseGenOnTinySA Off 100KHz-1MHz.PNG

  • Power On
  • Lot more energy at ~400 KHz
  • -30 dB

NoiseGenOnTinySA On 100KHz-1MHz.PNG

Rigol DS1054Z Measurements[edit]

    • 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)

Better Design[edit]

  • C1 is connected Emitter of Q1 to GND to reduce power supply noise
  • Higher noise than EMiRFD design
  • Falls off in a straight line (in dBm) with frequency
    • Usable from 1-10 MHz
    • -40 dBm at 1 MHz
    • -80 dBm at 30 MHz
  • Nearly zero power supply current

Better Noise Gen schematic.png

  • Off

V2-NoiseGenOnTinySA OFF 1MHz-10MHz.PNG

  • On, 1-30 MHz

V2-NoiseGenOnTinySA On 1MHz-30MHz.PNG

  • On, 1-10 MHz

V2-NoiseGenOnTinySA On 1MHz-10MHz.PNG

Even Better Design?[edit]

  • Previous design is probably good into receiver but not as good for tinySA tracking generator
    • Want to be able to drive passive/crystal filters for testing
    • Can already use NanoVNA but I'd prefer the tinySA
  • Goal
    • Flatter response across 1-30 MHz
  • Transistor seems to be a better noise source than a zener
  • Idea - replace amp stage with cascode output stage followed by emitter follower for better match to 50 ohm load
  • Example cascode design

CascodeExample-720px.jpg

  • Replace R1 with 0.1uF in parallel with 470K (from the the previous)
  • Remove R2

Cascode design[edit]

Cascode2.PNG

Cascode2 Sch.PNG

Cascode Videos[edit]

Build / Enclosure (Original board design)[edit]

  • 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[edit]

RF Noise Generator Rev 1