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Control Panel (CP) Board
The CP (Control Panel) circuit board contains all of the KX2’s control circuitry as well as IF and AF stages for the
transmit and receive paths. It contains two on-board microcontrollers: one to manage the radio (MCU), and another
to process all transmit and receive signals digitally (DSP).
The synthesized, digitally controlled local oscillator (LO) provides quadrature signals to the transmit and receive
mixers.
The DSP is a 32-bit, floating-point device. All modulation, demodulation, AGC, filtering, equalizing, and other
signal processing functions are handled by this IC.
The incoming IF signal from the RF board is provided in low-level phase quadrature, or In-phase and Quadrature
(I/Q). These signals are digitized by a very low power, high-performance analog-to-digital converter (ADC), then
passed to the DSP for processing.
The baseband transmit signal is likewise provided in I/Q format to the RF board. A dedicated, high-performance
digital-to-analog converter (DAC) is used to generate a very clean transmitted signal.
DSP program storage is by means of a 2 megabyte FLASH memory device. This IC also provides storage of
operator messages for the DVR function.
Stereo (two-channel) audio from the DSP is converted to analog signals for use with headphones or dual external
speakers (PHONES jack). The use of stereo allows special processing to help reduce operator fatigue (audio
effects), and also optimizes dual watch capability, where the signals from VFOs A and B are routed to the left and
right audio channels. If the internal speaker is used, the audio is monophonic, and is boosted by a separate speaker
amplifier IC. Microphone audio (or low level audio from a computer or or other source) uses another ADC that
runs at all times to enable voice-operated transmit (VOX) operation.
The microcontroller unit (MCU) handles all user interface functions for the KX2, including 12 switches and 4
shaft encoders. It also handles timing, sequencing, and overall management of the radio. The MCU uses EEPROM
to store operator preferences, messages, and settings. An accessory port (ACC) provides a serial I/O interface
between the MCU and an attached personal computer (PC), with both RS232 and USB cabling options.
The MCU uses two industry-standard serial protocols to control circuitry on the CP and RF boards. I2C
(pronounced I-squared-C) controls the synthesizer IC. An SPI bus handles bandswitching, changeover between
receive and transmit, etc. The driver for the liquid-crystal display (LCD) is also controlled via the I2C port.
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