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CT-X User’s Guide
22137813, Rev. 000 Feb 2020 25
Chapter 2 Setting up Your CT-X
Locating positions for signals
When determining signal locations in the spectrum, you should take the following into
consideration:
y
Is the frequency being considered already in use by any local broadcasters (or other
off-air signal sources such as LTE cellular, etc.)?
If yes, it is best to avoid these regions as the meter will either not see the signal of
the CT-X, or sensitivity will be compromised. Generally, the further away from such
signals the better.
y
Signals must be inserted directly between channels, not anywhere in their
bandwidth
y
Will Seeker D meters be using the CT-X signals?
If yes, a signal location(s) is needed in their usable frequency range (135–139 MHz
and/or 610.5–615 MHz)
y
Will an OFDM channel be used for leakage detection?
If yes, note the following: PLC location in MHz, subchannel spacing in KHz, and cyclic
prefix in µs for use in setting up the Seeker X meter.
No CT-X settings are required for DOCSIS 3.1 OFDM leakage measurements.
y
Spread remaining signals across the spectrum used by the channel plan to assure
good coverage and eliminate ingress near the most important channels in the lineup
Measuring metrics of adjacent channels
A signal is meant to be transmitted at a high enough level to be detectable but low enough
that it does not interfere with the signals on one or both sides of the carrier. These two
opposing requirements create an optimal level for the signal to be transmitted at. This
process is on a per-signal basis, so each signal will need to go through this process.
To find the optimal level, we will first need the adjacent power level of channels on either
side. Use the instrument to measure these metrics. Note that the channels should be
measured after the plant is combined with the output of the CT-X: