Promax PROLINK-4C, Manual

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USER’S MANUAL. PROLINK-4C
02/2003 Page 47
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4.9.1.5.3 Measuring BER of QPSK Digital Channels (QPSK)
Press the rotary selector to access the QPSK signals parameters that must be
defined by user and that are described below:
1) Symbol Rate
It is possible to choose between the following values : 30000, 27500, 22000,
20000, 19995, 6110, 6000, 5998, 5632, 5062, 4340, 4000 kbauds, or well to
define any other value (Other).
When selecting the Other option, a screen titled QPSK SYMBOL RATE will
appear. This screen shows present value, to modify it press key and
enter the new value through the keyboard. The unit accepts any number with 5
figures between 2000 and 35000 kbauds (fifth figure acts as validation). For
example, to select a symbol rate of 8200 kbauds it must be entered : 08200.
2)
Code Rate
Also known as Viterbi ratio. It defines the ratio between the number of data bits
and actual transmission bits (the difference corresponds to the control bits for
error detection and correction).
It permits to choose between 1/2, 2/3, 3/4, 4/5, 5/6, 6/7, 7/8, 8/9 and Auto. If
Code Rate parameter is not known it is possible to assign the Auto option.
3) Spectral Inv.
If necessary, activate the Spectral inversion. Reception will be bad if spectral
inversion has been incorrectly selected.
4) Attenuator
It permits to select attenuation between 0 and 30 dB. It is advisable to activate
the 30 dB attenuator under that measurement conditions where the signal level
is near to the maximum input level (approximately starting from 20 dB under the
maximum level) and it is possible that the tuner becomes saturated. Under no-
saturation conditions, when increasing the attenuation value the BER measure
must to maintain or to increase (insufficient signal level) but never to decrease.
Once you have defined the QPSK signal parameters, it will be possible to
measure the BER. When the BER measuring mode is selected, the monitor will show a
picture like the following: