RF Noise Generator

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

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)

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

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

• 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

• High Pass filter
• 5th Order Chebyshev filter
  • Fc = 1 MHz
  • 3 Inductors, 2 Capacitors
• Toroid Coil Winding Calculator

Schematic - 5% Standard parts

Predicted Response

Toroid winding

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

• Toroid Winding Calculator

High Pass Performance

Assembly Sheet

RF Noise Generator Rev 1