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K1 / K2 - Low Power on 20 Meters
Date: Wed, 10 Jan 2001
Please note that the 8-50pF trimmer caps used in the 20m band-pass filter can sometimes be difficult to adjust. This can often be corrected by
spinning the trimmers 10-20 times to allow the rotor and plate of the cap to seat. The caps will then often behave better, have more maximum C, and may be much less "touchy" to adjust. If the caps were installed so they properly match the silk-screened PCB outline, you may use a metal screwdriver to adjust them. The screw slot will be at ground potential, so there's no need to use the plastic tuning tool provided for the inductors, which can flex and make adjustment of the trimmers more difficult.
In rare cases, a few 8-50pF trimmers will not have sufficient maximum C to peak the filter on 20m. In that case, either add a 10-22pF fixed cap across the trimmer that is low in capacitance, or contact us and we will ship you replacements. Be sure to first properly peak the 30m inductors at L8 and L9, as these coils are also used for the 20m band when the trimmers are switched into the circuit.
The capacitance of the trimmers is at maximum when the metallized portion of the rotor's top is directly over the flat on the capacitor's base.