CBWI December 1996 Cobra 148GTL & Uniden Grant XL Unlocked Clarifier Mod.
Many of you already know that the 148 GTL and Grant XL are the same radio. The same board was used in the Cobra 2000 GTL. These chassis are remarkably stable after the clarifiers are opened and expanded. Although they do drift until warm, it's not much compared to the DX radios that have the same clarifier capabilities.
The following will unlock and keep the standard clarifier range:
1. Remove D58
2. Follow the wire (white or green) from R44 and remove the other end from the PC board and connect it constant +8 volts (IC4 pin 3).The following instructions will expand the clarifier range after it is unlocked:
3. Jumper R175
4. Jumper from R174 #244 side to D51 #246 side.
5. With a frequency counter connected to TP1 and clarifier control in the 12 O'clock position adjust the following:
L23 controls AM = 34.7650 MHz
L22 controls LSB= 34.7635 MHz
L59 controls USB= 34.7665 MHz
The Cobra 200OGTL is the same as above including the following steps:
Remove the blue and brown wires from the fine clarifier control.Add a 2K resistor from the empty end terminal of the fine clarifier potentiometer.Set both clarifier controls to 12 O'clock and adjust as above.
The dual controls on the 2000 are easy to deal with for the fun range of the clarifier. All that's needed to drop 5 KHz or 10 KHz is to get close with the coarse and trim in with the fine control.
The single controls are more difficult but the schemes listed above make them fairly easy to tune at the center slot position.
A dual potentiometer can be added to most radios. The only limiting factor is the space available in the front panel. Radios with the controls mounted flush to a circuit board behind them would take more work than it would be worth.
The following is a schematic for a fine/coarse clarifier control:
These could be two separate controls Fine Coarse but one dual potentiometer would be best. The 2K resistor can be larger or smaller depending on the range you prefer from your fine control.
Decrease the value to increase the fine range and increase the value to decrease the fine range.