Deviser S7200 User Manual page 49

6-5.4 Eye Diagram
Another way to determine the signal quality is with the eye diagram. Look for the seven "eyes" down the
center of the display, formed by intercrossing lines. If some eyes are not fully "open", the signal is not clear
enough. A perfectly compacted signal appears as clear open eyes.
6-5.5 Spectrum Mask
In the US, the FCC has specified different emission masks for different types of 8-VSB DTV transmitters. One
mask is specified for Full Service digital transmitters. Two other masks – termed "Simple" and "Stringent" –
are specified for digital LPTV (Low-Power Television) transmitters, Class A digital transmitters and digital TV
translators. The conditions imposed by the licensing process and the FCC's regulations should be consulted
to determine which mask is appropriate for a given digital transmitter (below, right).
If you receive a "FAILED" message immediately on entering the spectrum mask function, you may need to
adjust the attenuation. Tap ATT to open the attenuation submenu, then tap Input to enter a value or
Inc/Dec to adjust it up or down.
The spectrum mask function also supports a list display mode, showing major frequency points and the
pass/fail rating and signal strength at each (below, left).
Part II: Settings and Measurements
49