E.F. Johnson Company 5100 ES, Service Manual

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5-2 5100 ES Series Portable Radio Service Manual January 2007
Circuit Description
• User Interface (UI) Board
• Five flex circuits that provide interconnection with the RF board, display, top panel
controls, side buttons, and UDC (accessory) connector.
The UI Board provides the input/output interface for the user. It contains the PowerPC
processor which is the main controller for the transceiver. It also contains the keypad and
has inputs for the various buttons and switches. It also controls the display and performs
all RS-232 communications between the radio and remote computer stations for the
purposes of radio programming, tuning, encryption key loading and software
downloading.
The Logic Board contains the digital audio processing circuitry that includes the CODEC
and DSP devices.
5.1.2 Analog Mode
5.1.2.1 Receive Mode
The signal is routed from the antenna connector to the RF Board where it is filtered,
amplified, and mixed with the first local oscillator frequency generated by the synthesizer.
The resulting IF signal is also filtered and amplified and sent to the AD9864 digital IF
chip.
The signal is then mixed with the second local oscillator frequency to create a second IF
signal. The second IF signal is then sampled and downconverted to baseband. The
baseband signal is then decimated to a lower sample rate that is selectable at 20 kHz. This
signal is then routed via a serial interface from the IF chip to the DSP on the logic board.
On the logic board the DSP digitally filters the input signal and performs frequency
discrimination to obtain the message signal. The DSP first performs a carrier-detection
squelch function on the radio. If a signal is determined to be present, the audio portion of
the signal is resampled and then filtered appropriately. The filtered signal is then routed
back to a D/A in the CODEC to produce an analog signal for output to the audio power
amplifier and then the speaker. Any detected signaling information is decoded and the
resulting information is sent to the microcontroller.
5.1.2.2 Transmit Mode
The signal from the microphone is amplified and then routed to the CODEC chip where it
is first digitized and then sent to the DSP. The DSP performs the required filtering, adds
the desired signaling, converts the sample rate and then sends the resulting signal back to a
D/A in the CODEC to produce the analog modulation signals for the VCOs. The
modulated VCO signal is then sent to the RF power amplifier and transmitted.