Symptom:
3rd order IMD figures have been noted that do not meet out standard value of -32 to -35 dB.
Cause:
We have found that this symptom can be caused by either improper blas to the final transistor and/or because of distortion inducted by the 73.05 MHz IF mixer circuit.
Parts required:
R195, R197, R198 150 ohm chip resistor RK73FB2A151J QTY. 3
R204 4.7 Kohm chip resistor RK73FB2A472J QTY. 1
R19, R20 22 ohm carbon resistor RC05GF2H220J QTY. 2
Procedure:
- On the Final unit (X54-3450-00) change R19 and R20 from 10 ohm to 22 ohm. Figure 1.
- On the IF unit (X48-3100-00): Figure 2.
- Change R195 from 56 ohm to 150 ohm.
- Change R197 from 220 ohm to 150 ohm.
- Change R198 from 220 ohm to 150 ohm.
- Change R204 from 10 Kohm to 4.7 Kohm.
No additional adjustment or modification will be required.
Caution: This modification requires soldering equipment rated for CMOS type circuits. It also requires familiarity with surface mount soldering techniques. If you do not have the proper equipment or knowledge do not attempt this modification yourself. Seek qualified assistance.
Time required for this modification is 1 hour or less.
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