2-3
plugged into the unit. Hum is measured in-service using DSP
algorithms. Preprogrammed filters help isolate power supply
problems to one times power-frequency, two times-power-frequency,
or all low frequency components.
Depth-of-Modulation
Depth-of-modulation, activated by the MOD Measurement Mode key,
can be measured in service. This display also allows the user to
listen to either AM or FM audio carriers to help identify a signal or
troubleshoot some problems. If a steady ingress source is found,
this feature can be used to help find out what is leaking into the cable
network.
Carrier-to-Noise (C/N) Measurement
Press C/N to make this performance measurement. The C/N is a two
step measurement requiring you to “take down” or turn off the
carrier--after the SAM 4040D makes an initial measurement--so that
the instrument can measure the noise. The SAM 4040D will prompt
you when to turn the carrier off, and then prompt you to turn it back
on.
Carrier-to-Noise is measured using an advanced ‘quiet line’
algorithm. The SAM 4040D meter searches for a line of video with
no active signal (This typically happens on one or more lines during
vertical sync of an analog video channel). This allows the noise
measurement to be made in the middle of the channel rather than in
an unused side band. Thus, the reading reflects what the CATV
subscriber really sees.
Sweepless
Sweep
Activated by pressing the Sweep Measurement Mode key,
Sweepless
Sweep allows a technician to get sweep information
even if no transmitter is available. In Sweepless
Sweep, a SAM
4040D unit measures the stable carrier levels and memorizes them.
These levels can then be compared with the levels of the same
carriers at a different point in the network, and differences in
frequency response can be highlighted.
First, scan and learn the carriers at a point in the CATV network to
which you want to normalize all other measurements. In an HFC
network, this is typically the first forward test point after the optical