4-36
Cisco uBR7200 Series Universal Broadband Router Hardware Installation Guide
OL-5421-03
Chapter 4 Connecting the Cisco uBR7200 Series Router to the Cable Headend
Measuring the Upstream RF Signal
Note
Refer to the documentation that accompanied your particular spectrum analyzer for detailed instructions
on activating and positioning the trigger line.
A known workaround exists for the Agilent 8591C spectrum analyzer. After activating and positioning
the trigger line in video mode, you
must
press the “video” button on the spectrum analyzer once more to
enable proper functionality.
Step 8
Adjust the amplitude on your spectrum analyzer so that the uppermost portion of the upstream RF signal
is in the top graticule of the analyzer’s display grid and adjust the trigger line accordingly. Your spectrum
analyzer will then display an upstream RF signal similar to the one shown in
Figure 4-40
.
Note
We do not recommend using the spectrum analyzer’s “max-hold” feature while analyzing upstream
signals in the frequency domain. “Max-hold” readings in the frequency domain can be inaccurate
because the analyzer focuses on the peak power of the strongest ranging modem rather than the power
levels of cable modems that are operating in a more ideal range.
Figure 4-40
Measuring the Upstream RF Signal—Accurately Measured Amplitude on Spectrum
Analyzer
Step 9
Position a marker about 7/8 of the way into the preamble of the signal, as illustrated in
Figure 4-40
. (The
preamble is the regular pattern displayed at the front of the signal and the length of the preamble is a
function of the channel width/data rate, modulation format, and DOCSIS burst-profile configurations.)
The peak amplitude of the marker, which reg31.07 dBmV in this case, will be within 1 dB of the
true burst power.
Note
To verify this reading, you can also measure the power rating with an Agilent 89441A vector signal
analyzer (
http://www.home.agilent.com/agilent/home.jspx?cc=US&lc=eng)
.
If the preamble of your upstream signal is displayed with a significantly lower amplitude than the rest
of the RF signal, refer to the
“Using the Zero-Span Method with Adjacent Upstream Channels” section
on page 4-40
for instructions on how to overcome this phenomenon.
Содержание 7246 - uBR Router
Страница 16: ...xvi Cisco uBR7200 Series Universal Broadband Router Hardware Installation Guide OL 5421 03 Preface ...
Страница 18: ...xviii Cisco uBR7200 Series Universal Broadband Router Hardware Installation Guide OL 5421 03 Preface ...
Страница 238: ...Index IN 10 Cisco uBR7200 Series Universal Broadband Router Hardware Installation Guide OL 5421 03 ...