Promax PROLINK-4C, Manual

Page: 204 / 334

USER’S MANUAL. PROLINK-4C
Page 84 02/2003
Imagine a situation like the one shown in the next figure: a digital channel (8
MHz BW) adjacent to an analogue channel. When measuring C/N for the digital channel
in TV mode using the Auto setup, the analogue channel may interfere in the noise
measurement (given that the noise level is measured at fnoise=ftuning - ½* Channel
BW = 650 MHz - 4MHz = 646 MHz), so under this situation it is recommended to make
the measurement in Spectrum Analyser mode and to define manually the frequency
where we want to measure noise (obviously a frequency where no signal is present);
i.e. in the next figure noise is defined to be measured at 655 MHz.
Figure 42.- Carrier to Noise measurement in Spectrum mode (digital channel).
To define the frequency to measure the noise, select the Reference noise
function in the Spectrum functions menu and press the rotary selector. Next, again in
the Spectrum mode, turn the rotary selector to place the marker on the frequency where
you want to measure noise level or press key [31], current reference noise value
will be erased and using the keyboard introduce the new value. Finally accede to the
functions menu again and execute the Carrier function so that you can tune new carrier
frequencies by turning the rotary selector.
When C/N measuring mode is selected, on the lower part of the image appears
the tuned frequency/channel (Carr.), the noise frequency (Noise), the carrier Level (if
analogue mode is selected) or the channel Power (if digital mode is selected) and the
carrier to noise ratio (C/N).
4.10.2.3 Measuring the Power of Digital Channels (Channel Power)
In the Spectrum Analyser mode the PROLINK-4C measures digital channel
power using an Integration method between channel limits which are defined by the
user. To show the interest of this method, imagine a spectral distribution like the one
shown in the following figure (channel bandwidth is 8 MHz defined by the markers). If
channel power is measured in TV operation mode different readouts will be obtained
depending on the tuned frequency (measurement filter bandwidth is 230 kHz), if tuning
is shifted from 759 MHz to 762 MHz reading will increase in several dB.