Cherokee Radios CBS2100
Documentation Project
CBTricks.com

PLL ALIGNMENT

Connect the radio to 13.8V DC power supply, terminate the antenna terminal by a 50ohm 20W dummy load. Turn on the frequency counter, oscilloscope, digital multimeter and the radio, wait 30 minutes before adjusting any frequency determining components.

A. Reference Oscillator Frequency Check [10.2400 MHz]

1. Connect the frequency counter to pin terminal between C-83 and C-85.
2. Check counter reads 10.2400 MHz.
3. Tolerance within ± 200 Hz is acceptable. Otherwise replace the 10.24MHz crystal. (if frequency error is more than ± 500 Hz, change C-81 for other values for freq. Correction)

 

B. Second Offset Frequency Oscillator Check 10.695MHz [AM] 10.6925MHz [LSBI 10.6975MHz [USS].

1. Connect frequency counter toTP-6 (C73/D27).
2. 10.695MHz AM operation, Set the mode selector to AM, and press PTT key switch to transmit, adjust L-26 to obtain 10.695MHz (+0, or -100HZ) on the frequency counter.
3. 10.6925MHz LSB operation: Reset mode selector to USB. Adjust L-27 to 10.6925MHz, +0, or -100HZ.
4. 10.6976MHz USB operation: Reset mode selector to LSB. Adjust L-28 to 10.6975MHz, +0, or -100HZ.

 

C. PLL Mixer IC Input Level Adjustment

1. Set the mode selector to AM, and the Clarifier Control to center position. Set channel selector to CH 20.
2. Connect Oscilloscope to TP4 between C-106 and L-50.
3. Adjust L-22 for maximum RF to the Mixer input.

 

D. PLL VCO Adjustment

1. Set the mode selector to AM, and the Clarifier Control to center position. Set channel selector to CH 20.
2. Connect Oscilloscope to TP-3 at R74.
3. Adjust L-18 for maximum VCO RF output.
4. Connect DC voltmeter to TP-2 between R-116 and R-117.
5. Adjust L-17 to obtain DC 3V ± 0.1V VCO Control Voftage.

 

E. PLL Off-set Frequency Adjustment

1) Receiving Mode:

1. Connect frequency counter to TP-3 at R74.
2. Set the mode selector to AM, and the Clarifier Control to center position.
3. Set channel -selector to CH. 20.
4. Adjust L-19 for 16.510 MHz + 50Hz.
5. Set the mode selector to USB.
6. Adjust L-20 for 16.5125 MHz ± 50Hz.
7. Set the mode selector to LSB.
8. Adjust L-21 for 16.5075 MHz 50Hz.

 

2) Transmiting Mode:

9. Set the mode selector to LSB, and press PTT to transmit.
10. Hold-on Tx key switch [PTT] and adjust Trimmer Pot. VR-15 for frequency correction to 16.5075 MHz ± 50Hz, release PTT and observe the frequency is the same for Tx and Rx.