Part II: Settings and Measurements
8-7.2
Group Delay Analysis
The group delay function is primarily used to verify flatness of the usable frequency band close to filter
rolloffs, typically on the upper side of a reverse diplex filter (42MHz in US, 55MHz in Japan, 65MHz in Europe,
but soon to be considered at 85MHz or even 200MHz when entering an extended D3.0 or D3.1 network
environment). This is especially true when more than one active is in cascade, and would potentially make
the rolloff curve worse. DOCSIS does specify a theoretical maximum group delay of 200ns / MHz, but using
75ns/MHz or less is recommended for best results.
There are two horizontal markers available automatically detecting min/max delay. The differential value is
displayed at the top right corner of the graph. A vertical marker is available to measure frequency and
time delay value at every point of the curve by rotating the rotary knob. The data is displayed at the
bottom of the screen.
Group Delay Analysis
Button Operation
Equalizer: Display the equalizer coefficient.
Freq Response: Display the in-band frequency response.
Group Delay: Display group delay information.
Marker: Control manual marker operation.
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