Promax PROPOWER - 5 Manual De Instrucciones página 68

I. Absolute method
Selecting in the Channel-Frequency configuration menu the NOISE MODE
parameter as FREQ, the equipment will interpret the NOISE FREQ. value as the
frequency where the noise power measurement must be done. Naturally the user must
be sure that the NOISE FREQ. value corresponds with a free channel.
II. Relative method
Selecting in the Channel-Frequency configuration menu the NOISE MODE
parameter as F, the unit will make the measurement of noise at the frequency obtained
to add to the tuning frequency (channel central frequency) the value defined for the
NOISE FREQ. parameter. The PROPOWER-5 takes by default NOISE FREQ. = BW/2,
where BW is the channel bandwidth defined in the channel plan, thus for example, if it is
desired to measure the C/N ratio of a digital PLC channel with a bandwidth (BW) of 2.5
MHz, NOISE FREQ. will take as value 1.25 MHz. The Channel-Frequency configuration
menu (paragraph 4.2.3.3) allows the user to redefine this parameter; when tuning a new
channel the equipment will return to assign to NOISE FREQ. the default value.
The following figure shows that when making C/N measurements in the relative
method (∆F), it is essential to bear in mind the presence of adjacent channels;
otherwise, the noise could be confused with the signal of another channel.
Figure 16.- Example of digital channels spectrum.
Taking as example the previous figure, if we suppose that for the channels that
appear in the figure it has defined a bandwidth of 2.5 MHz, in the relative mode of
measurement the PROPOWER-5 will take as value for NOISE FREQ. = 1.25 MHz.
Note that this method can cause erroneous measures in the measurement of the
channels.
For D24 it is advised to configure NOISE FREQ = -1.75 MHz and to verify if the
measurement increases. In case a channel has two adjacent channels (for example
channel D25) it is recommended to select the absolute mode and to assign to the
NOISE FREQ. parameter a frequency corresponding to a free channel (for example
between D26 and D27).
Page 20
BW=2,5 MHz
USER'S MANUAL. PROPOWER-5
07/2006