Motorola MICOR PL Filter

By Kevin K. Custer  W3KKC

Concept and Circuit Description:
This is an image of a PL tone filter to be used with a Motorola MICOR mobile or basestation conversion to repeater. The frequency response and equalization it provides is different than the original MICOR circuitry, and provides a more robust sound, especially on the bottom end of the voice range. The inductor and capacitors are salvaged from an old Motorola MOTRAC Hiband or UHF mobile unit.  The inductor, a 6 Henry choke is Motorola part number 25C82024D02.  The part can also be salvaged from a MICOR PL receive deck, although the part number is different.  This circuit should be driven by a discriminator buffer amplifier. The buffer amp is fed from pin 3 of the Audio & Squelch board (emitter follower out). In some units the value of the input cap. was .033uF and a 220K resistor was added in parallel to the inductor. Either version works fine.   This circuit may be used in other makes and models of equipment.

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