Using Spectrum Analyzer Features
Using limit-line Functions
The LIMITS FRQ TIME key selects the type of limit line parameters. Parameters can be entered as frequency/amplitude coordinates, or as time/amplitude coordinates. Use the LIMITS FRQ TIME key, to underline the desired choice of either frequency or time parameters. Frequency
is the default selection. If TIME is selected SELECT TIME will replace
SELECT FREQ in the Edit Limit menus.
The second column of the limit line table is labeled START-FREQ when frequency is selected. It is labeled START-TIME when time is selected.
The LIMITS FIX REL key selects the type of limit line. There are two types of limit lines: fixed and relative. Fixed limit lines contain only absolute amplitude and frequency (or time) values. Relative limit lines consist of frequency values that are referenced to the cable TV analyzer’s center frequency and amplitude values that are relative to the analyzer’s reference level. The relative setting does not affect time values. They always begin at the left edge of the graticule.
As an example fixed versus relative limit lines, if a limit line is specified as fixed, entering a limit-line segment with a frequency coordinate of 300 MHz displays the limit-line segment at 300 MHz. If the same limit-line table is specified as relative, it is displayed relative to the cable TV analyzer’s center frequency and reference level. If the center frequency is at 1.2 GHz, a relative limit-line segment with a frequency coordinate of 300 MHz will display the limit-line segment at 1.5 GHz. If the amplitude component of a relative limit-line segment is - 10 dB and the cable TV analyzer’s reference level is - 15 dB, then - 10 dB is added to the reference-level value and the amplitude component of the limit line will be at -25 dB.
RELATIVE is displayed in the limit-line table when the limit-line type is relative; FIXED is displayed when the limit-line type is fixed. A limit line entered as fixed may be changed to relative, and one entered as relative may be changed to fixed. When the limit-line type is changed, the frequency and amplitude values in the limit-line table are modified by the current center frequency and reference level settings to keep the limit line in the same position on the cable TV analyzer.
