IC-746 FAQ
6.15
How do I adjust the LCD display?
Page 66 of the Instruction Manual describes how to change both the LCD contrast and the
LCD backlight.
Push MENU to select M2.
Push button to select LCD.
Push buttons to select lighting or contrast.
Turn the tuning knob to adjust value.
6.16
The Noise Blanker doesn't seem to do any good. What's wrong?
Probably nothing. Possibly your expectations.
Noise blankers are placed in the IF signal path, and designed to gate/mute/attenuate out
impulse noise. Impulse noise is characterized by very sharp pulses (steep rise time and short
duration). Such noise is typically a result of ignition spikes and certain types of power-line
noise.
A good clue comes from the 746 service manual.
The NB adjustment procedure uses
square wave pulses 30 mv high and 1 msec long.
Therefore, a NB is not a panacea. Unlike an ANL or DSP, a NB will have little or no effect
upon static crashes and/or white noise. Noise generated by power supplies, fluorescent
lights, and power inverters are generally unaffected.
The NB works best when impulse noise is strong and the signal is weak; like mobile in a
vehicle.
Most hams report that the 746's NB is effective against ignition noise, but not as effective as
other rigs they've owned.
Noise blankers are not all that sophisticated, and will try to blank out anything that resembles
an impulse; even sharp voice peaks in an audio signal. Sometimes, the NB will generate
more noise than it removes.
The IC-746 NB is operating within the first IF, where the passband is about 15 Khz wide.
Any impulse like component of a nearby strong signal may activate the NB, again possibly
doing more harm than good. Also, strong nearby signals can fool the NB into fluttering the
receive audio.
The single best way to deal with impulse noise is to eliminate it at the source. A NB (any
NB) is a compromise solution at best.
Page 76 of 113
2003-02-08
Содержание IC-746
Страница 36: ...IC 746 FAQ Page 36 of 113 2003 02 08 ...
