Frequency Counter

From Land Boards Wiki
Jump to navigation Jump to search

FreqXounter-Kit-Assembled-02.PNG

Features[edit]

Built into case[edit]

  • P-Touch white on black labels

FreqCounter-P181-720px.jpg

Plastic 100x60x25mm-720px.jpg

Power 5-1mm.PNG

  • 7-9V in
  • Right angle header pins pointing to inside of card
  • 4-40 x 3/16” Machine Screws
  • 4-40 Standoffs

FreqCounter-Case-11-720px.jpg

Rework - Add Pre-Amp[edit]

  • Re-uses extra HF transistor that would have been used by crystal tester oscillator
  • AC coupled input
  • Based on

Pre-Amp schematic[edit]

FreqCounter PreAmp Schematic.PNG

When building kit, do not install[edit]

FreqCounter DoNotInstallParts.PNG

Cuts/Jumpers[edit]

  • Four cuts
    • Blue = 1 front side cut
    • Green = 3 back side cuts
  • Jumpers Red

FreqCounter Rework PCB Front.PNG

  • Green = Back side cuts

FreqCounter Rework PCB Back.png

  • Short etch on one cut

FreqCounter Rework-Cuts-Back.PNG

  • Details of preamp input pin

FreqCounter Rework-06.PNG

  • With parts

FreqCounter-P177-720px.jpg

  • Wire on back

FreqCounter Rework Wires Back.PNG

Initial Testing[edit]

FreqCounter InCase.jpg

  • 4.9152 MHz crystal oscillator
    • Scope frequency counter shows 4.19520 MHz
    • Freq Counter displays 4.9747 MHz
    • Difference = 500 Hz or 0.1% accuracy
  • Can only adjust the variable capacitor in narrow range
  • Freq = 25,000 MHz - measured = 24.997 MHz
    • Error = 3 KHz / 25,000 KHz = 0.012%
  • Freq = 10.000 Hz - measured = 9.999 Hz = .01% error

Fixing the frequency error[edit]

  • Calibrated using VFO-001 calibrated to WWV
  • Replaced 22 pF cap with 2 series 33 pF caps
    • Far right near variable cap

FreqCounter-P177-720px.jpg

  • Added 22 pF to back of board
    • Upper mid right

FreqCounter-P180-720px.jpg

  • Why was this an error?
    • Perhaps the variable cap is too small for proper loading of the crystal
    • Could possible parallel a 10 pF cap with the variable cap?

Firmware Mods[edit]

Reviews / Builds[edit]