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3.3 Front Panel Bar-Dot Displays
Bar-dot LEDs show audio input levels, wideband and highband audio gain control, and
modulation percentage. Resolution for the gain control and modulation displays is increased
over a conventional bar-graph display using dither enhancement which modulates the
brightness of the LED to give the effect of a fade from dot to dot. (See section 4.7.)
3.3.1 Audio Processor Input
Two vertical, moving-dot displays for the left and right channels indicate the relative audio
levels, in 3 dB steps, at the input of the audio processor. Under normal operating conditions,
the left and right Audio Processor indicators will be active, indicating the relative audio input
level after the Input Gain switches. During program pauses, the red Low LED will light.
The translator configuration shows relative audio levels from the included receiver.
3.3.2 Highband and Wideband Display
During audio processing, the moving-dot displays indicate the amount of gain control for
broadband (Wide) and pre-emphasized (High) audio.
As long as program material causes activity of the Wideband green indicators, determined
by the program source level and Input Gain switches, the transmitter will be fully modulated.
(See section 3.4.)
The Wideband indicator shows short-term "syllabic-rate" expansion and gain reduction
around a long-term (several seconds) average gain set. In the translator configuration, the
Wideband indicator also shows relative RF signal strength.
Program material and the setting of the Processing control determine the magnitude of the
short-term expansion and compression (the rapid left and right movement of the green
light).
High-frequency program content affects the activity of the Highband indicator. With 75–µsec
pre-emphasis, Highband processing begins at about 2 kHz and increases as the audio fre-
quency increases. Some programs, especially speech, may show no activity while some
music programs may show a great deal of activity.
3.3.3 Modulation Display
A 10–segment, vertical peak-and-hold, bar graph displays the peak modulation percentage.
A reading of "100" coincides with 75 kHz deviation. The display holds briefly (about 0.1 sec-
onds) after the peak. The "Pilot" indicator illuminates when the transmitter is in the stereo
mode.
To verify the actual (or more precise) modulation percentage, connect a certified modulation
monitor to the RF monitor jack on the rear panel.
Operation
3-5
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