Elecraft K3 Owner's Manual - Manual (Page 73)

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through of the local oscillator (synthesizer) signal. The mixer also incorporates a balanced VHF low-pass filter
to suppress both internally and externally generated VHF/UHF spurs. This keeps the K3’s HF spur complement
extremely low, despite the use of a down-conversion system architecture.
KAT3 (ATU) and KANT3
The basic K3/10 includes a KANT3 antenna input module. If you’ve ordered a KAT3 antenna tuner, the
KANT3 is not required and will not be supplied with the kit. In either case, the module plugs into the RF board
at the back-right corner. Both the KANT3 and KAT3 provide antenna surge protection, as well as resistors for
bleeding off static DC charge. The KAT3 provides a wide-range, switchable C-in/C-out L-network for matching
a variety of antennas with SWR as high as 10:1 (100 W) or 20:1 (10 W). There are 8 inductors and 8 capacitors
in the L-network, each switched with a DPDT relay for high reliability. The KAT3 also includes a second
antenna jack and associated switching relay. There’s an additional jack on the board for routing the unused (non-
transmit) antenna to the KRX3 sub receiver module.
KIO3 (AF/Digital I/O)
All audio and digital/computer I/O is routed through the KIO3. The KIO3 is made up of three PC boards: Main,
Audio IO and Digital IO.
The Main KIO3 board plugs directly into the RF board. It includes a relay to disconnect the right speaker
channel in case a mono speaker is plugged into the external speaker jack, isolation transformers for Line In and
Line Out signals, a connection point for the internal speaker, a low-noise oscillator to provide voltages for the
RS232 serial interface, and various control line inputs and outputs for external transverters, band decoders, and
the like. This board also contains a differential output microphone amplifier to equalize the gain between the
front and rear microphone jacks, as well as to provide noise immunity for the microphone signal from the rear
panel area.
Circuitry to allow use of the serial port RTS or DTR signal lines as PTT and/or KEY inputs is also located on
this board. This feature is to support logging and control programs which may use these lines for controlling
transmit/receive switching or CW keying.
The Digital IO board plugs into the KIO3 Main board. It includes a DE-9 serial port connector for use with an
external PC, and a DE-15 accessory connector for external band decoders (such as the KRC-2), transverters
(such as the Elecraft XV-series), and similar devices. It is also the connector to which direct FSK or PSK
signaling is applied.
The Audio IO board includes three stereo outputs: headphone jack, speaker jack, and a transformer-isolated Line
Out jack. It also provides two monophonic inputs: microphone and an isolated Line In. The Microphone jack
can provide bias for an electret microphone when enabled via the MAIN:MIC SEL menu entry.
Both Digital and Audio IO boards include extensive bypassing and decoupling to help prevent RF signals
getting into the radio through cables attached to their respective connectors.
Front Panel and DSP
The Front Panel is a large plug-in module that includes both the Front Panel and DSP boards, as well as the Aux
DSP (if a sub receiver is installed) and digital voice recorder module (if the KDVR3 option is installed).
Front Panel Board
This board provides the K3’s user interface: 35 custom-labeled switches; two dual-concentric potentiometers for
gain and squelch control; seven shaft encoders; custom, 240-segment, high-contrast LCD; and 13 discrete LED