Integrating SDR and Standard Transceiver

This article details the integration of a Software Defined Radio (SDR) with a standard transceiver (TRX), power amplifier (PA), and antennas. It presents a solution for connecting an SDR to an existing ham radio station without modifications. The core of the system is a splitter box that ties the antenna input/output of the TRX and the antenna input of a direct conversion receiver (DC RX) together in RX mode. In TX mode, the DC RX input is grounded via a fast telecom relay controlled by the transceiver's -SEND signal. A 10ms delay is incorporated for safety. The splitter includes a 3.7 dB input attenuator for impedance matching and acts as a "fuse" to protect the DC RX input. Ground loops are avoided using common mode balun transformers, and the DC RX input is insulated with a broadband transformer. An accompanying audio switch box allows listening to the main transceiver, SDR output, or both simultaneously (split into left and right earphones). The article mentions a kit available for this integration.