DEVA Broadcast DB4005, Инструкция по техническому обслуживанию и эксплуатации

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Header Area
Header is located on the left quarter of the screen. Depending on contents of working area the
header may contains the following items:
- Frequency Indicator showing the currently selected frequency is located in the
upper left corner. Frequency’s resolution is 0.01 MHz;
- Currently selected active RF or MPX Input.
ANT 1 – signal being processed is the one from the Antenna 1 Input. MPX – input from MPX
Input;
- Attenuator Indicator – showing the currently selected position of the active
Input. Attenuator’s position can be set manually by the operator or automatically be the DB4005.
- Indicator for Stereophonic Information contained in the received signal and currently
selected de-emphasis time constant.
- Indicator for RDS information contained in the received signal.
- Decoded
PS
information from RDS signal;
- Indicator to show the signal level at the antenna input;
- Indicator to show the phones audio level;
- Indicator to show currently selected IF band-pass filter bandwidth;
Having three different de-emphasis selections, the question arises which one to select? As well
known, one of the problems with the high quality VHF FM transmissions is that the increased
audio bandwidth means that background noise can often be perceived. It is particularly noticeable
towards the treble end of the audio spectrum, where it can be heard as a background hiss. To
overcome this it is possible to increase the level of the treble frequencies at the transmitter. At
the receiver they are correspondingly attenuated to restore the balance. This also has the effect of
reducing the treble background hiss which is generated in the receiver. The process of increasing
the treble signals is called pre-emphasis, and reducing the treble signals in the receiver is called
de-emphasis. The rate of pre-emphasis and de-emphasis is expressed as a time constant. It is the
time constant of the capacitor-resistor network used to give the required level of change. In the
UK, Europe and Australia the time constant is 50µs whereas in North America it is 75µs.
So it can be selected depending on the region you are located or to completely disable this
feature.