HP 8591C, Руководство пользователя, Страница: 263 / 373

Test Descriptions
Carrier-to-Noise Ratio Test Description
2. Disable modulation
The second method is an interfering measurement of carrier-to-noise in
and measure over FCC
which modulation is removed. The marker is positioned within the displayed
range
FCC measurement range. Averaging can be selected to stabilize the noise
measurement.
Before returning to the main menu, the modulation must be turned back on
3. Non-interfering The third method is called in-channel non-interfering carrier-to-noise
(using Option and
measurements (Option 107 required) in which the gating function is used to
measure over FCC range
make the measurement with video modulation on. This method is enabled
with the GATE ON OFF key after the carrier-to-noise test has been started. A
horizontal line with no test signals or data within the active line time is found
(quiet line). In h
c annel measurement mode, the CONTINUE is then
pressed to execute the measurement.
The analyzer displays the in-channel noise measured only during the quiet
line. The minimum level noise is not found. Instead, noise can be measured
over a range to account for possible non-flatness of the noise floor.
FCC 76.609(e) requires a noise integration be made over the full range if the
noise floor is not flat. The outer markers in this test show the range over
which the noise is integrated. Because of the presence of the visual carrier,
integration over the full 4 MHz cannot be done. However, 85% of the entire
range is integrated. See Figure 8-3.
The outer markers that are used to determine the range are set by
pressing the INTGRTN
SET in channel measurements mode. Gated
carrier-to-noise shows in-channel noise delivered in the video in addition to
RF noise of amplifiers and
equipment. Troubleshooting can be done
without interrupting service. Advertisement insertion equipment may yield
different results when active.
8-10