Colpitts Crystal Oscillator

Features

• Colpitts Crystal Oscillator
• Useful for binning crystals
  • Hand select close values from a pile of crystals
  • Useful for design of crystal filters
• Made from junk box parts
  • (2) 2N3904 transistors
  • Standard value 1/4W resistors
• Design from Experimental Methods in RF Design - Fig 7.69
  • Built by others (W2AEW, IMSAIGuy, etc)
• Runs from 4V to >16V
  • May run at higher voltages, didn't tempt fate
• 15mA with 4.44 MHz crystal at 12V

Tested With

• 4.433 MHz crystal - worked
• 16 MHz crystal - worked
• 27 MHz crystal - didn't work

Prototype

• Cut square PCB material for raised pads
• Build on single side Copper clad PCB material
• Large ground plane

Prototype Scope Caps

UUT = 4.4433 MHz crystal

• Rigol DS1054Z - 50 MHz scope (100 MHz mod)
• UltraScope
• 8 Digits Frequency Counter shows 4.432298 MHz
• Waveform triangular

• FFT
• 0-50 MHz
• Shows lots of extra noise
  • In plastic box

• Fundamental - zoomed in

• FFT 3rd harmonic
  • 3rd harmonic down about 20 dB

UUT = 16.000 MHz crystal

• Sinewave is cleaner

W2AEW Video

• Wes Haywood EMiRFD cirvuit

PCB

Assembly Sheet

Colpitts XTAL Oscillator Rev 1 Assembly Sheet