http://www.synergenics.com/sc/faq.htm
What's a "simplex autopatch"?
A simplex autopatch is a system which allows telephone calls to be placed over the air, using a single frequency for transmit and receive. Usually, a conventional transceiver is used to build such a system, rather than a separate transmitter and receiver.
The tricky part is deciding when to transmit and when to receive, while a phone call is in progress. EchoStation supports the "time-sharing" technique -- periodically, it switches the transceiver very briefly from transmit to receive, just long enough to detect if a signal is present. A few modern FM rigs can be used for Simplex Autopatch without modification.
While EchoStation does support Simplex Autopatch, this mode is not currently recommended due to hardware-compatibility issues. Very few FM rigs can accommodate the fast T-R switching required, without modification.
