1
st
Mixer
The 1
st
mixer combines signals from the input band-pass filters with the output of the synthesizer to obtain the
1
st
I.F., at 8.215 MHz. The mixer is based on a video switching IC with very low ON resistance, resulting in low
loss and high signal-handling capability. Since this type of mixer requires low drive, there’s very little leak-
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 HF spur complement
extremely low, despite the use of a down-conversion system architecture.
KAT3A (ATU) and KANT3
The basic K3S/10 includes a KANT3 antenna input module. If you’ve ordered a KAT3A 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 KAT3A provide antenna surge protection, as well as resistors for
bleeding off static DC charge. The KAT3A 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 KAT3A 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 KRX3A sub receiver module.
KIO3B (Audio/Digital I/O)
All audio and digital/computer I/O is routed through the KIO3B. The KIO3B is made up of three PC boards:
Main, Audio IO and Digital IO.
The Main KIO3B 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, USB and RS232 serial interfaces, 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.
The USB port provides a single-cable solution for most PC interface needs, including both control and line-level
audio in/out. When the USB port is in use, line-level analog audio is digitized by the KIO3B module and routed
to the USB connector itself. This eliminates the need for a computer sound card and associated cables.
Circuitry to allow use of the USB or RS232 port’s RTS or DTR signals for PTT and/or KEY inputs is also
located on this board. This supports logging and control programs which may use these lines for controlling
transmit/receive switching or CW keying.
The Digital IO board plugs into the KIO3B Main board. It includes a USB connector, an RJ45 connector for use
with RS232 communications and/or the P3 panadapter, and a DE-15 accessory connector for external band
decoders (such as the KRC2), transverters (such as the Elecraft XV series), and similar devices. The DE-15 is
also used for direct FSK or PSK signaling.
The Audio IO board includes three stereo outputs: headphone jack, speaker jack, and a transformer-isolated Line
Out jack. It also provides two mono 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.
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).
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