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 drift until warm, it’s not much compared to the DX radios with the same clarifier capabilities.
The following will unlock and keep the standard clarifier range:
- Remove D58
- Follow the wire (white or green) from R44, remove the other end from the PC board, and connect it to constant +8 volts (IC4 pin 3). The following instructions will expand the clarifier range after it is unlocked:
- Jumper R175
- Jumper from R174 #244 side to D51 #246 side.
- 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.
Uniden Grant Clarifier Modification
This one is similar to the Washington chassis but already has the 11.3258 MHz crystal in the circuit. The 5.6µh choke is needed for the extra range, and a super diode in place of the stock varactor diode would give the best range.
The following instructions will open and increase the clarifier range:
- Remove D52
- Remove R148
- Remove R174
- Remove C121
- Jump the diode next to the D52 location.
- Lift the ground side of D20 and install a 5.6µh choke from the open lead of the diode to the ground.
- Follow the red wire from the clarifier control and disconnect it from this point, then solder it to ground.
- Follow the orange wire from the clarifier control, disconnect it from this point, and solder it to +8 Volts constant (IC4 pin 3).
- Set the clarifier to the 3 O’clock position.
- Connect a frequency counter to TP1 on channel 40.
- In USB, adjust CT3 for 35.0075 MHz.
- In LSB, adjust L19 for 35.0025 MHz.
- In the AM, adjust L20 for 35.0050 MHz.
There are other radios that use these chassis and the mods would be the same. You’ll just have to determine which chassis are the same by looking for commonalties for yourself.
What is the primary objective of the clarifier modification for the Cobra 148GTL and Uniden Grant XL radios?
The clarifier modification for the Cobra 148GTL and Uniden Grant XL radios aims to unlock and expand the clarifier range, enhancing the radio’s tuning precision and performance.
How can the clarifier range be expanded after it is unlocked?
To expand the clarifier range after unlocking, you should jumper R175, create a jumper from R174 #244 side to D51 #246 side, and adjust specific components (L23, L22, L59) with a frequency counter connected to TP1, ensuring the clarifier control is in the 12 O’clock position.
What is the significance of the 5.6µh choke in the Uniden Grant Clarifier Modification?
The 5.6µh choke is essential for providing the extra range in the clarifier. It should be installed by lifting the ground side of D20 and connecting the choke from the open lead of the diode to the ground.
How can one set the clarifier for different modes after the modification?
After the modification, with the clarifier set to the 3 O’clock position and a frequency counter connected to TP1 on channel 40, adjustments should be made as follows: In USB, adjust CT3 for 35.0075 MHz; in LSB, adjust L19 for 35.0025 MHz; and in AM, adjust L20 for 35.0050 MHz.
What is the purpose of the dual potentiometer in the clarifier control scheme?
The dual potentiometer can be added to most radios to provide fine and coarse clarifier control. It allows users to achieve precise tuning using two separate controls or a single dual potentiometer. The 2K resistor can be adjusted to modify the fine control range, depending on user preference.