Planar IT-14 Operating Manual page 11

1 – channel number
2 – channel level measured in dBmV, dBuV or dBm
3 – selected frequency in MHz
4 – V/A ratio in dB
5 – command line with commands activated by F1, F2 or F3 keys
6 – channel name (when working with selected channel plan)
7 – direct voltage or effective alternating voltage at the input of the Analyzer, at 50/60 Hz frequency, in V
8 – C/N ratio in dB.
When digital channel level is measured you will see D message instead of V/A or C/N on the screen.
When you open LEVEL mode, you can see channel plan name indicated by «Plan:», if one has been
selected.
When the LEVEL function is activated, the IT-14 measures the parameters of the TV channel which was
last selected in one of the measurement modes. This mode will be indicated by Ch shortcut in command line.
The channel modulation type (digital or analog) corresponds to the selected channel plan. If the channel plan
has not been selected, the modulation type is determined automatically.
Three parameters are measured for analog channels. Video carrier level is measured in the frequency
point defined in accordance with the channel template for operation without channel plan. If channel plan has
been selected, the frequency point will be taken from this channel plan. To determine V/A ratio, the Analyzer
additionally measures the audio carrier, which is defined in accordance with the channel template. The V/A
value will be displayed on the screen in position 4 (Figure 4.3.5).
To measure C/N ratio the Analyzer performs measurement in the frequency point with the lowest content
of the useful components of RF signal within the channel bandwidth. If a channel plan has been selected the
measurement frequency will be defined by the channel plan, if not, it will be defined automatically by means
of searching the optimal frequency within frequency offset range of minus 1.500 to minus 1.000 MHz
relatively to video carrier frequency. C/N ratio will appear in position 8 (Figure 4.3.5). The C/N ratio will be
calculated by the following formula:
C/N = Uch – Unoise – 10Lg(Bch/Bm) – K, where
C/N – carrier to noise ratio value;
Uch – channel level;
Unoise – noise level;
Bch – video channel bandwidth;
Bm – measurement channel passband;
K – correction factor.
When working with selected channel plan C/N ratio measurement can be switched on/off separately for
each channel (Section 4.4.2). When working without channel plan C/N ratio measurement can be swithced
off for all channels by means of channel template (Section 4.9.6).
For digital channels the Analyzer measures signal power within the channel bandwidth.
To perform this measurement, the Analyzer applies the integration method. The IT-14 calculates the total
signal power value by measuring the power within all of the channel bandwidths in 125 kHz increments. It
then recalculates the total value into actual power value using the following formulas:
Bch
[
. 0 125
∑
Ui /
Usum =
10
=
i 0
(
⋅ log Usum +
Uch =
20
Ui – signal power value in i-point of the channel;
Вch - digital channel bandwidth in MHz;
Usum – total signal power value in the channel bandwidth, uV;
Uch - actual channel power in dBuV;
К - correction coefficient.
The value of the Bch bandwidth is determined by the channel plan (Section 4.4.2) or channel template if
no channel plan has been selected (Section 4.9.6). The K constant are determined empirically.
To increase the accuracy of the measurement operating with a channel plan, set the digital channel
parameters (Section 4.4.2) to their optimal values.
]
20
)
, where
K
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