KENWOOD TH-21 A/AT
EXPANDED RF 140-159 MHz
1 Disconnect the battery and antenna.
2. Remove knobs, antenna nut ring and plastic top
3. Remove front panel.
4. Locate switch unit. (PCB X41-1590-00) This unit has the Vol, Sqh etc.
5. Cut trace between R1 and D4.D5
6. Install a jumper from the common point of R11, R5 & 5C to the corner of the tone switch.
7. Install a 1N914 diode and 48K resistor from the center top pin of the tone switch to the end of resistor R1. (R1 was cut in step 5).
Note: Cathode end of the diode goes to the tone switch top center pin. Cathode end of a diode has the line.
8. Adjust L10, L11, L12, L13, TC1, TC2 & TC3 for maximum upper frequency range.
9. Reassemble the radio.
Depress the tone switch to receive from 140 to 149 MHZ Tone switch off for 150 -159 MHz.