T.E.M. A07B500S, Руководство пользователя

Страница: 28 / 131

A07B500S manual
Pag. 28
The previous eight screen shots, if selected, allow to perform the measurement of the modulation
analysis according to the CEPT 54-01rule. For an exhaustive explanation of this new measurement
method see chapter 7.
Briefly, it can be said that a music signal can exceed the limit threshold of 75kHhz, provided that
this exceeding is contained in a certain percentage. The rules concerning this topic are contained in
the above mentioned regulation and in the IEC-244. Thus it’s possible to quantify the excess of over
modulation peak and it’s possible to show, as in the appendix, that the numerical factor K fixing
this limit can not be greater than 0.2. Modulation power on the opposite can not be higher than the
one relating to a sine signal deviating 19KHz (reference =0dB)
The observation period, for the measurement and the calculation of these factors, is 1 minute, after
that the result will be displayed.
For the calculation of the K over modulation peak factor, 1200 samplings are performed during a 60
sec measurement, and the value factor is obviously 0 if no peaks exceed 75KHz. The value 0.2 is
acceptable as a higher over modulation limit; the value 0.5 shows that the modulation must be
reduced of 1dB at least, values higher than K indicates strong over modulations.
For the modulation power, over 10 millions of samplings are performed during the minute of
examination and power integral defined in the measurement segment is calculated; the result is
compared to the one equivalent to a sine signal which deviates 19KHz; the result of the comparison
is expressed in dB and it must not be higher than 0, in order to make the measurement complying
with the rule. This limit is debatable and, as it has been described in chapter 7, normally in on-field
measurements the values of 2,3dB are found which, after all, we estimate don’t cause over
modulations.
Since the peak modulation values are random (they depend, besides on the set levels, on the type of
musical pieces as well), K or PM values can remarkably vary during the day relating to the type of
the transmitted program; it’s useful to do many measurements at different times by trying to
measure dance-music rather than spoken. By using the Personal-Computer interfaced with COM1
placed on the front panel it’s possible to perform this measurement with many hours of observation
periods as it will further be seen.