Icom IC-251A Instruction Manual page 5

SECTION Il DESCRIPTION
144MHz ALL-MODE TRANSCEIVER INCORPORATING A MICROCOMPUTER
CPU control with ICOM's original programs provides various operating capabilities. No-backlash
dial controlled by ICOM's unique photo-chopper circuit.. Band-edge detector and Endless System
provides out-of-band protection. No variable capacitors or dial gear, giving problem-free use.
The IC-251A/E provides FM, USB, LSB, CW coverage in the 144~146MHz (IC-251A: 143.8 ~
148.2MHz) frequency range. Thus the IC-251A/E can be used for mobile, DX, local calls, and
satellite work.
MULTI-PURPOSE SCANNING
Memory Scan allows you to monitor three different memory channels. Program Scan provides
scanning between two programmed frequencies. Adjustable scanning speed. Auto-stop stops
scanning when a signal is received, in all modes.
DUAL VFO'S
Two separate VFO's can be used either independently or together for simplex operation, and any
desired frequency split in duplex operation.
CONTINUOUS TUNING SYSTEM
ICOM's new continuous tuning system features a luminescent display that follows the tuning knob
movement and provides an extermely accurate readout. Frequencies are displayed in 7 digits
representing 10OMHz to 100Hz digits.
Automatic recycling restarts tuning at the top of the band, ie., the high edge when the dial goes
below the low edge. Recycling changes the high edge to the low edge as well. Quick tuning in
1KHz steps is available, and fine tuning in 100Hz steps in the SSB and CW modes, and 5KHz steps
and 1KHz steps in the FM mode, is provided for trouble free OSO.
EASIER OPERATION AND LIGHTER WEIGHT
The most compact, lightest weight all-mode 144MHz transceiver. First to use a pulse power supply
in communication equipment, for lighter weight. 50mm-diameter large tuning control knob for
smooth and easy tuning. Trouble-free controlling knobs for both receiving and transmitting.
LED indicator for transmit and receive modes.
MOST SUITABLE FOR BOTH FIXED AND PORTABLE STATIONS
Built-in 117V/240V AC and DC power supplies. Convenient Dial Lock switch for mobile opera-
tion. Easy-carry handle. Effeetive Noise Blanker to reduce outcoming pulse noise. 1C-SM5 high
quality stand microphone is suitable for fixed station operation. Powerful audio output, 1.5 watts
at 8 ohm, for easy listening even in noisy surroundings.
OUTSTANDING PERFORMANCE
The RF amplifier and first mixer circuits using MOS FET's, and other circuits provide excellent
Cross Modulation and Two-Signal Selectivity characteristics. The IC-251A/E has excellent sensi-
tivity demanded especially for mobile operation, high stability, and with Crystal Filters having
high shape factors, exceptional selectivity.
The transmitter uses a balanced mixer in a single conversion system, a band-pass filter and a
high-performance low-pass filter. This system provides distortion-free signals with a minimum
spurious radiation level.
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