OVERVIEW

This article is written for Motorola Micom Mobat users that need to add a capability to support digital communications, such as the MT63-1KL and MT63-2KL modems supported by the FLDIGI application.

ABOUT

The Motorola Micom Mobat provides a 44-pin accessory connector on the back of the radio, which supports balanced audio circuits for both transmit audio input and receive audio output. The Micom Mobat service manual explicitly warns against grounding one side of the balanced audio interface circuit to obtain an unbalanced audio interface circuit. The TigerTronics SignaLink USB provides unbalanced audio circuits for both the transmit and receive audio. Interfacing the SignaLink to the Micom Mobat requires using two 600Ω 1:1 audio transformers to convert between the Micom Mobat balanced audio circuits and the SignaLink unbalanced audio circuits. The circuit below can be used to implement the interface between the Micom Mobat and SignaLink. The circuit uses a 6-pin Mini DIN connector, and is compatible with the SignaLink SL-USB-6PM (see this product ).

Also included in the schematic, but not necessary for digital communications operating modes, is a cable that adapts the serial interface on the Micom Mobat microphone connector to a D-SUB 9-pin serial port connector. This cable is used to program the Micom Mobat radio. An FTDI or similar USB to serial adapter can be attached to this cable to use a USB interface to program the radio.

SCHEMATIC

Click HERE to download a pdf copy of the schematic.

PHOTOS

EXCEPTIONS

It should be noted that the Micom Mobat enclosure will not accomodate a standard housing on the 44-pin accessory connector. It might be possible to remove some material from a standard connector housing in order to get the housing to fit on the radio, but such an endevour is left up to you to experiment with.

The Micom microphone will be HOT during digital transmissions. Either the operating room must be kept quiet or the microphone should be unplugged from the Micom during digital transmissions to avoid unwanted modulation.

PARTS LIST

All components can be purchased from DigiKey.

Part	URL
44-Pin D-Sub Connector	digikey.com/product-detail/en/amphenol-icc-fci/10090770-S444ALF/609-4047-ND/2350305
6-Pin Female Mini DIN Connector	digikey.com/product-detail/en/cui-devices/MD-60CV/CP-2860-ND/352863
600Ω 1:1 Audio Transformer	digikey.com/product-detail/en/tamura/TTC-5029/MT7213-ND/674292
Plastic Enclosure	digikey.com/product-detail/en/hammond-manufacturing/1591LBK/HM113-ND/130898