11
Introduction
The Barrett 2000 series transceiver has been designed to take advantage of the latest technology whilst
remaining simple in architecture and construction. Having two main PCB’s, the PA and the Micro/RF PCB
the transceiver is housed in a rugged enclosure using aluminium extrusions.
Receive current consumption has been reduced to a low 470mA and the receiver has been designed
specifically for high dynamic range by the use of digital switching mixers.
A Digital Signal Processor (DSP) and Programmable Gate Array (PGA) based microprocessor is the core of
the transceiver performing many of its functions
This technical manual covers the Barrett 2050 transceiver, the Barrett 2055 receiver, the Barrett 2050M
transceiver module and the Barrett 2040 man-pack adaptor. The receivers and transceivers have largely
identical hardware and software and only vary by function.
The use of DSP in the receiver
Extensive but sensible use of Digital Signal Processing is used in the receiver design. The received audio
signal is both switched and filtered as required by an inbuilt Digital Signal Processor. In addition, some of
the receiver audio tones, such as
alarm tones and SELCALL send audio, are generated, and switched by
the DSP. This has removed the need for much of the circuitry required for the formerly complex audio
switching.
The receiver's automatic gain control time constants are also handled by the DSP. This makes possible
specialised AGC characteristics where required. For instance a "hang" AGC is standard for the 2000 series,
but other systems can be applied as required.
The DSP is also used for Selcall and ALE tone detection, Syllabic and SSL mutes generation and noise
reduction.
The use of DSP in the transmitter
The transmitter power output is entirely controlled by the DSP, from the action taken to reduce power when
a serious antenna mismatch occurs, to reducing power in the event that the temperature becomes
excessive.
The Automatic Level Control or ALC is processed by the DSP. This allowing time constants within the ALC
loop to be individually setup for a particular transmission mode.
Other refinements
The transceiver's controlling microprocessor consists of a large Programmable Gate Array, or PGA. This
guards the transceiver against standard microprocessor obsolescence.