Measurement Of Analog Channel Undesirable Modulation (Hum) - Planar IT-100 Operating Manual

maximum permissible tap gain value according to ETSI TR 101290. The ECHO
MARGIN column displays the worst-case difference between the permissible
value and the value measured at all taps, i.e. this value indicates the noise margin
of reflected signals level;
2) Freq. Response. This mode displays the amplitude to frequency response of the
channel calculated from the equalizer impulse response characteristic. Frequency
offset in reference to the channel center and the response level in dB in the cursor
position are indicated in the bottom of the screen. Response flatness in dB is
indicated in the FLATNESS column;
3) Group delay. This mode allows viewing channel group delay, calculated from the
equalizer impulse response. Frequency offset in reference to the channel center
and delay value in ns in the cursor position are indicated in the bottom of the
screen. Response flatness in ns is indicated in the FLATNESS column.

4.3.8. Measurement of analog channel undesirable modulation (HUM)

This mode allows viewing relative level bar graph of harmonic component of analog
channels undesirable modulation, as well as total relative level of undesirable modulation
in the channel frequency band. The screen view and the data displayed are presented in
Fig. 4.16.
The relative level value of undesirable modulation is measured using the following
formula:
HUM[%] = ( Lmax – Lmin ) * 100 / Lch, where
Lmax – maximum level of parasitic component in the measurement interval,
Lmin – minimum level of parasitic component in the measurement interval,
Lch – average carrier level value in the measurement interval.
Measurement results analysis of undesirable modulation level of separate harmonic
component enables qualitative evaluation of the nature of distribution network problem.
High value of fundamental harmonic (50 or 60 Hz) usually indicates the problem with
power sources of signal generation and distribution equipment. High value of second
harmonic (100 or 120 Hz) indicates the problem with the equipment grounding circuit,
which is the reason of parasitic signal rectification.
Total relative level of undesirable modulation in the channel frequency band enables
numerical determination of the video and sound quality. It is indicated in the HUM
parameter line to the right from the bar graph.
The power grid frequency is selected in the terrestrial TV channels setting mode
(section 4.3.2).
Figure 4.16
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