T.E.M. A07B500S, Manual

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A07B500S manual
Pag. 50
with coloured noise as mentioned in the CCIR 559 rule (annex B). The process is described in the
IEC 244-13 standard and consists of modulating the transmitter with noise as above, with a
deviation equal to 32KHz. This work condition corresponds to the maximum allowed band
occupation and to a radio broadcast spreading dance-music which modulates ±75KHz.
At these conditions (modulated transmitter with coloured noise in accordance to CCIR-559) there is
the chance to have a reference of a radiophonic transmitter at frequency modulation which occupies
the maximum allowed spectrum and on which it’s possible to perform all the modulation
measurements repeatedly, having some parameters as results which can be applied and compared on
the field to modulation measurements of a network which is broadcasting a normal music program.
The music signal can not be surely measured by a normal detector with effective or peak value,
differently from a fix tone signal. The measurement must be done, being not sinusoidal or other
periodical form, detecting the power of the signal self (function proportional to its instantaneous
value square) or the peak with very long observation periods.
7.2 Modulation peak analysis measurement
The CEPT 54-01 rule shows, in its paragraph
4.2, how the peak measurement must be performed on
the modulation of a frequency modulation transmitter.
The maximum deviation peak must be found in a 50msec window, to be sure of catching also
modulating frequencies till 20Hz. At each minute 1200 representative peak modulation samples are
available.
These values, obtained with even many minutes long observation periods, will be placed into a
graph in the following manner:
on the abscissas, the frequency deviation will be placed with a deep scale of 150KHz
on the ordinates the number of samples of the corresponding deviation value will be placed
It maybe by extreme examples it’s possible to explain the concept better. Suppose to modulate the
transmitter with a fix tone having a deviation of ±75KHz and to perform the peak measurement in
object for a period of 10 minutes. Thus 12000 samples all with the value 75 will be obtained: the
graph will be of a single vertical line 12000 high and placed on the abscissa 75 (fig. 5.a).
On the opposite if we modulate the transmitter for 3 minutes with ±20KHz deviation, then
for further 3 minutes with ±40KHz and at last for further 3 minutes with ±50KHz and the
observation period fixed at 9 minutes we will obtain 10800 samples 3600 of which will have
abscissa 30, other 3600 samples abscissa 40 and the last ones abscissa 50 (fig. 5.b).