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FC-390 Frequency Counter Modification


  1. You must accept responsibiliity for any losses that may occur from the use of any of the information contained on this site.
  2. Any modifications that you do - are done at your own risk !
  3. The modifications page is for educational purposes only, many of the examples are illegal in most countries!


FC-390 Frequency Counter

Using the FC-390 frequency counter on the Texas Ranger TR-296, Cobra 148 (any version), or Uniden Grant XL or LT series requires one modification. 

  1. Remove the four (4) screws holding the top and bottom case together.
  2. Seperate top and bottom plastic covers, exposing internal metal case.
  3. Carefully remove the top metal cover from case. This will expose the component side of the pc board.
  4. Find JP1 - located to the right and below the crystal.
  5. Carefully solder a buss jumper between the top and bottom holes, as shown in yellow in the below photo.
  6. Re-assemble counter, and follow installation instructions supplied with unit.

Installation Wiring Diagram for Texas Ranger TR-296 or 148-GTL

FC-390 Foil

Foil Side View 
Click to view full size Here