In 1995, I conducted an experiment at the joint of two office Fax machines through the air. For this purpose we used two УSW radio stations in the range of 145 MHz. Faxes were connected at the speed of 2400 bps.
The interface circuit shown in the figure.
Because the Fax operates in half-duplex mode, the task of the interface is to switch the radio from reception to transmission, i.e. the connection to the device speaker or microphone.
As the transformer was used transformer from the modem (you can try to use the transformer from the telephone). All transistors type KT315, diodes - KD522. LED - AL307.
Author: Reinier van der Lee, PA3DJM, Vienna, translated by N. Bolshakov; Publication: N. Bolshakov, rf.atnn.ru