BPF Selector Introduction


This stage adds the RX/TX BPF Selector functionality to the I2C bus.

The actual filter builds will be addressed in separate stages

The microprocessor controls whether PTT is on or off (switching the selected filters into the TX or RX paths) and issues band-select words to the band-switching circuitry to activate the desired filter from among the (up to) 8 available filters.

It is always a good idea to double check the bill of materials in this set of documentation with the official BOM on the Mobo site. Discrepancies may be introduced inadvertently, as the changes are sometimes not communicated or discovered, making timely update of this site a problem.

Theory of Operation

The 8 filter banks, represented by P3 through P10, are selected using two FST 3251 switches, both gang-controlled by the PC 8574's 3 pins P0-P2. The selected filter is routed to either the transmit or receive path by a single FST 3253, depending upon the state of the PTT line.

The signals actually being switched are: