Revision 1.0
4
Copyright FlexRadio Systems, 2010-2011
Theory of Operation
Refer to the Block Diagrams on the two following pages.
The detailed schematic are included in Appendix “A” and Appendix “B”.
The unit is powered by +13.8 Volts DC, supplied via the 2.5 mm x 5.5 mm coaxial power
connector on the rear of the unit. The unit has an internal 3.0 Ampere fuse that will blow
if the unit draws excessive current or if the polarity of the power connected to the unit is
reversed.
The FLEX-1500 CPU (TAS1020B Streaming USB Controller) will communicate via
USB for both control and streaming baseband data with the host CPU running the
PowerSDR software. The CPU in the FLEX-1500 has control of all switching, signal
routing, frequency generation via the DDS, FlexWire port, audio amplifier, as well as
audio and baseband routing, CODEC clock generation, data conversion, gain and level
controls for the radio.
Communication between the Flex-1500 radio and the host computer is via a USB
connection capable of USB 1.1 or higher level USB operation. The protocol is USB
“Full Speed” or 12 Megabits per second data transfer rate.
Power Systems and Distribution
The transceiver board requires a source of regulated +5 Volts at approximately 400 mA
to function. +3.3 Volts is supplied to the board in general by a linear +3.3Volt regulator
derived from the +5 Volt line. Additional +3.3 Volt and +1.8 Volts required to operate
some of the integrated circuits is provided by point-of-load regulators in the vicinity of
the IC.
Overall power for the unit is derived from the +13.8 Volt input on the RFPA board.
This 13.8 Volts directly supplies the relays and power amplifier transistors. It is also
feeds two regulators. A 6 Volt regulator is switched on when transmitting, and off when
receiving. This switched +6 Volt output is used to bias the RF power transistors. A
separate +5 Volt regulator supplies power for the SPI decoder and relay driver IC on the
RFPA board, as well as supplies all +5 Volt power to the transceiver board (PTRX) via
the board to board interconnect system.
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