ELECRAFT KX3 Owner's Manual page 50

to great lengths to minimize distortion, trading off circuit cost and complexity against the benefit of reduced
interference.
Keyer: A device that partially automates the sending of Morse code, allowing for faster code speeds. The KX3
has a built-in keyer function, as well as an optional attached keyer paddle (KXPD3, pg. 25).
Linear power supply: A power supply that provides a well-regulated DC output voltage using analog regulator
circuitry. An analog regulator uses continuous voltage feedback, and can be designed to generate virtually no
noise at radio frequencies, at the expense of power-conversion efficiency. Linear power supplies also typically
incorporate a transformer and large filter components (capacitors and inductors), resulting in larger and heavier
packages than switching power supplies (see below).
MCU (microcontroller unit): A computer or controller usually integrated onto a single integrated circuit. A
modern amateur transceiver usually has one main MCU that controls most radio functions. It may have other
smaller MCUs or co-processors that perform specific functions. The KXBC3 option module has its own MCU
(pg. 25). The DSP in the KX3 is a form of co-processor.
MDS (minimum discernable signal): A measure of a radio's sensitivity, expressed in dB (decibels) relative to
1 milliwatt (0 dBm). For example, the user of a KX3 with the 20-dB preamp turned on, can typically copy a CW
signal at about -137 dBm, or 137 dB below 1 milliwatt.
Preamp: A pre-amplifier that increases RF signals to a higher level for use by subsequent stages in a receiver.
A preamp is generally designed to contribute little noise of its own, so that it improves the noise figure of the
radio (also see MDS). The KX3 includes two different preamps for use in different situations (pg. 13).
Roofing filter: A filter built with analog components that rejects some out-of-band signals which could cause
overload or distortion. The roofing filter appears ahead of the A-to-D converter and DSP in a receiver's signal
chain, protecting them to some degree. The KX3 has an optional dual roofing filter (see KXFL3, pg. 25.)
SDR (software-defined radio): A radio that performs signal modulation, demodulation, filtering, and other
functions in software. The software might execute internally in a dedicated DSP IC, as in the Elecraft K3 or
KX3, or externally in a general-purpose computer (pg. 26).
Switching power supply: A power supply that provides a regulated DC output voltage by rapidly injecting
current pulses into its load. The duration of the pulses varies with the required load current at any given instant.
The switching rates used in this type of regulator can be in the hundreds of kHz or even MHz, and their period
can vary widely. This is why such power supplies often generate RFI (radio-frequency interference) or hash if
not well-shielded and filtered. Switching supplies are typically much smaller than linear supplies (see above) for
a given output current, and are used in most PCs and other electronic equipment because of the reduced
manufacturing cost. However, much of the RFI heard in amateur receivers originates from switching supplies in
nearby gear or even from neighboring houses. The supply that powers the radio itself is especially critical, and a
linear supply will often provide better results.
VFO (variable frequency oscillator): A signal source used to select a radio's operating frequency. The KX3's
large knob controls VFO A, while a smaller knob controls VFO B (see Using VFOs A and B, pg. 11).
50