How I connect a serial data moden (GLB Electronics, (1985) to a serial port of a MDS data modem (iNET 900)?

Question

The modem radio is manufactured by GLB Electronics circa 1985, serial # 708105 (parallel port, 25 pins) The other radio is a iNET900, MDS, serial port, nine pins.

Answer 1

Most of the old serial communication was RS232. which was 1.5 to
5 volt TTL. You need the pin outs of each devices. Than jumper the transmit pins to the receive pins of the other devices. Similar to current loop. If there are enable pins simply pull then to the enable state an let it go.