AP401FULL-HD_rev.09_UK
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5.
C/N mode: allows for automatic or manual measurement mode to be selected for
measuring the signal-C/N noise ratio.
6.
C/N Prmt: this function is used to set the parameters (noise reference frequency)
necessary for automatic measurement mode.
4.7.3.
MEASUREMENT BANDWIDTH
Two bandwidths are available in terrestrial band,
n
(100 kHz) and
w
(1 MHz). Three bands
are available in satellite band:
k
(100 kHz),
n
(1 MHz),
w
(4 MHz). In order to select the
desired bandwidth, press the
MENU
button and turn the dial to select the “BW FILTER”
item. Press
ENTER
, turn the dial to make your selection and press
ENTER
again to
confirm. It is generally preferable to use the wider bandwidth since it is less critical, unless
there is any interference from neighbouring signals (for example, in television channels, the
stereo sound carrier can only be measured in “n” band since it would otherwise be
interfered with by the mono sound carrier). If in doubt, it is a good idea to verify the
difference in spread spectrum mode (see section 4.15).
4.7.4.
USING THE ATTENUATOR
The instrument’s full scale value depends on the inserted attenuation value. This value
ranges in steps from 0 to 60 dB. In order to control the attenuator, press the
ATT
button
and turn the dial. The inserted attenuation value will be indicated on the status bar at the
bottom of the screen.
When the attenuation value is inserted, the instrument will take it into account and will
indicate the actual input value. If the full scale value is exceeded, the symbol
>
will appear
next to the level measurement; in this case, the attenuation value must be increased. If the
symbol
<
appears, on the other hand, this means that the level is below the minimum
measurable value; in this case the attenuation value must be decreased. These two
operations will be carried out directly by the instrument if the attenuator is set to automatic
mode (in Spectrum Analyzer mode, the attenuator only functions manually). In order to
activate automatic mode, press the 2nd and ATT buttons in sequence.
ATTENTION
:
It is best to use manual mode when searching for the maximum or minimum level by tuning
or while performing other operations like positioning the antenna. Many expert operators
with greater knowledge of level variations prefer to use the attenuator in manual mode.
In the case of measuring pure noise or digital signals, it is important to understand that
these types of signals can easily saturate the inputs. The following considerations must
therefore be kept in mind:
•
The measurement should be carried out with the attenuator in manual mode, wherever
possible.
•
In order to make sure that the input is not saturated, check that the level measurement
does not change significantly when changing the attenuation.
•
The smaller the measurement bandwidth (w, n, k), the greater the risk of overloads.