Measuring The Power Of Digital Channels - Promax MC-377+ Instruction Manual

INSTRUCTION MANUAL MC-377+.

4.2.6.2 Measuring the power of digital channels

The main characteristic of digital signals is that they distribute their energy across
the entire channel bandwidth (in the same way as a noise signal), in other words they
do not posses a differentiated carrier. Given this different nature from analogue signals
the method used for measuring can not be the same. You must use a detector
appropriate for signals of a 'noisy nature' and take into consideration that the bandwidth
of the measuring filter is smaller than the bandwidth of the channel.
The MC-377+ takes into account the properties of digital signals and enables the
power of digital signals to be measured almost automatically, just follow the procedure
below:
- Select the Spectrum Analyser operating mode, SPAN mode, and with the help of
the frequency counter display [22] tune the signal using the TUNING [24] and FINE
TUNING controls [26]. Adjust the SPAN control [23] to select a bandwidth so that
the signal occupies the most part of the image.
- Select the digital signal measurement scale CH POWER [32], the DIG key [11]
should be in the pressed position and the DIGITAL indicator [30] should remain lit.
- Read the level on the screen with the help of the scale calibrated in dBµV
(25-75 dBµV) CH POWER [32]. If the level is very close to 75 dBµV or is greater
than this value, the signal should be attenuated using the RF attenuators.
- The actual signal level is calculated in the following manner:
Power [dBµV] = Reading [dBµV] + Atten. [dB] + Correction Factor [dB]
THE CORRECTION FACTOR IS OBTAINED FROM THE CORRECTION CHART
WHICH IS DELIVERED WITH THE INSTRUMENT. THIS VALUE DEPENDS ON THE
FREQUENCY.
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VERY IMPORTANT
May 2001