Planar IT-088, Руководство по эксплуатации

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Index 1 shows the measured level in dB related to 1 µV in the set point. To define V/A
and C/N ratios for analogue channels the IT-088 performs measurements in three
frequency points. The first one is the video carrier frequency (or the frequency your
Analyzer is set to). The second frequency point is the audio carrier frequency. The third
one is the point 0.5 MHz shifted down from the second one. V/A ratio will be indicated in
position indexed 4. C/N ratio will appear in position indexed 7.
The audio carrier frequency is defined in accordance with the frequency set by the
current TV system ( TV system, section 4.3.10).
The IT-088 offers the capability of the frequency point selection for optimization of noise
measurements while operating by channel plan. (4.4.2.1).
For digital channels your Analyzer will perform measurements of two parameters: actual
channel power within the channel frequency band and the ratio of the digital TV signal to
the noise in the channel.
There are two methods of the actual channel power measurement. In the fast scan
mode ( Scan mode: fast , section 4.3.10) power estimation is performed by one
measurement. The Analyzer will measure the channel power of the set frequency
(frequency value in the center of the channel) and then will calculate the actual channel
power according to the following formula:
Uac.dg = Um + 10*Lg (Bdg/Bm) + K, where
Uac.dg
- actual channel power;
Um - measured channel power;
Bdg - digital channel frequency band;
Bm - frequency band of the measurement;
K - correction factor.
This method is fast and rather accurate only if the spectrum is almost uniform
throughout the channel band. If the spectrum variation is high this method can give big
error.
In the integration method the Analyzer will perform measurements of the power within
the entire channel band with 125 kHz step, and then calculate the average value, and
recalculate it into the actual power value.
This method is slower, but more accurate. It can be enabled in the Scan mode: 1:1
(section. 4.3.10).
To define the ratio of the digital TV signal to the noise in the channel your Analyzer will
measure the noise outside of the channel band. The noise frequency shift is determined by
the channel plan (
«Fnoise» parameter).
The C/N ratio An will be calculated by the following formula:
An = Um - Un, where
Um - measured channel power;
Un - noise power.
Digital channel parameters (central frequency, bandwidth, frequency shift for noise
measurement) should be taken from the channel plan. To increase the accuracy of the
measurement you should set the values either manually or in auto mode (section 4.4.2.1).
While performing measurements for digital channels it is recommended to apply the
mode of calculation for the maximum values: Averaging: average 8 (section 4.3.10). This
method ensures more accurate results for wideband noise-like signals.
The remote cable power supply voltage is measured from 10 to 100 V. The absolute
error of the measurement is lower than ±1.5 V. The measured value of the voltage at the
Analyzer's input is indicated in position indexed 6. If the voltage is direct you will see
, if
the voltage is alternating you will see .