This is a description of a modification to the transmit audio circuit of conventional Maxtrac/Radius radios. The purpose of this modification is to improve microphone sensitivity and make the frequency response more pleasing to the ear. This modification is intended for Amateur Radio use only.

This modification works on all Radius M100 and M200 models. It also works on all conventional mode only models of the Maxtrac.

This modification is make to the transmit pre-emphasis circuit on the logic board. It should work for all four models of logic boards. This includes HLN5172A, HLN5173A, HLN9123A, and HLN9313A. The logic board must be removed from the chassis to modify it. The screws may have to be removed from the RF board for reinstallation after the logic board modification has been accomplished.

• Chip resistor R655 (bottom side of board) is changed to 2200 ohms.
• Chip capacitor C652 (top side of board) is changed to 0.033 uF.

Both must be changed. Reinstall the logic board and reassemble the unit.

Motorola part numbers:

• 2200 ohm chip resistor 06-11077A82
• 0.033 uF chip capacitor 08-11051A10

Disclaimer:

Modifications are performed at your own risk. Modifications have not been thoroughly tested. Draw your own conclusions. Look for adverse side effects such as PL talk off when using higher PL frequencies.

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