ComSonics QAM Marker User manual

User Guide
Document is subject to change. Please check www.ComSonics.com for updated information.
CSI Doc. 101623-004 eRev. 1.0.2

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
2
Limited Warranty (brief)
Hardware: ComSonics, Inc. (ComSonics) warrants to the original end user (Customer) that the new
ComSonics branded products will be free from defects in workmanship and materials, under normal
use, for one (1) year from the date of original shipment. ComSonics warrants repaired and
refurbished ComSonics products for ninety (90) days from date of shipment.
Software: ComSonics warrants to the Customer that the Workstation Application software will
perform in substantial conformance to program specifications for a period of ninety (90) days from the
date of original shipment. ComSonics warrants the media containing the software against failure
during the warranty period.
ComSonics makes no warranty or representation that the operation of software products will be
uninterrupted or error-free, or defects in the software products will be corrected.
Software License (brief)
ComSonics grants you, the Customer, a limited nonexclusive license to use the accompanying
software program(s) (the Software) subject to the terms and restrictions set forth in this License
Agreement. You are not permitted to use the Software in any manner not expressly authorized by
this License. You acknowledge and agree that ownership of the Software and all subsequent copies
thereof regardless of the form or media are held by ComSonics or its suppliers.
Complete Limited Warranty and Software License Agreement documentation is printed in the back
section of this document.
Technical Support
ComSonics maintains a Technical Support Service for customer convenience.
Phone [phone] or 1-540-434-5965 Monday - Friday: 8:00 a.m. - 5:00 p.m. Eastern Time
Fax: [phone], Email: [e-mail]
Copyright
All material in this manual is the property of ComSonics, Inc. and protected under the United States
copyright law. No material shall be reproduced or used in any form or by any means (graphic,
electronic, or mechanical, including photocopying, recording, taping, or information storage and
retrieval systems) without the written permission of:
ComSonics, Inc.
1350 Port Republic Road
Post Office Box 1106
Harrisonburg, Virginia 22801 USA
Phone: [phone] USA Toll Free: [phone]
Fax: [phone]
Email: [e-mail]
Internet: www.comsonics.com
Sniffer is a registered trademark of ComSonics, Inc.
QAM Sniffer, QAM Marker, Nexus, and GeoSniffer are trademarks of ComSonics, Inc.
© 2012 ComSonics, Inc. All Rights Reserved
Document 101623-004 eRev. 1.0.2
2013-12-18 jv

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
3
Table Of Contents
Table of Contents
Limited Warranty (brief)............................................................................................................... 2
Table Of Contents....................................................................................................................... 3
Electrical Safety .......................................................................................................................... 4
Introduction................................................................................................................................. 5
Components................................................................................................................................ 6
Headend/Hub Installation............................................................................................................ 7
DC Powering............................................................................................................................... 8
Power and Alarm Indicators ........................................................................................................ 9
Broadcast Insertion Considerations........................................................................................... 10
Configuration Manager Introduction (web based)...................................................................... 12
QAM Marker Manual Level Setup Procedure ............................................................................ 16
Spectrum Analyzer.................................................................................................................... 16
QAM Channel Measurement Reference Notes.......................................................................... 23
Worksheet for Manual Level Mode Setup........................................................................... 24
Specifications............................................................................................................................ 25
Limited Warranty....................................................................................................................... 27
Software License Agreement .................................................................................................... 28

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
4
Electrical Safety
This symbol is used to alert users of possible hazard or risk in operating this equipment.
Read the instructions fully before operating this equipment for the first time.
Do NOT expose this equipment to rain or moisture!
Do not disassemble the equipment or interfere with the internal components; this will void
the warranty and create the possibility of electric shock.
If the equipment is used in a manner not specified by the manufacturer, the protection
provided by the equipment may be impaired.
Only use the provided mains lead as using other types may cause damage to the
equipment, which will void the warranty and may cause electric shock.
Clean only with a soft dry cloth.
AC Mains.
This equipment does not have a power switch. It is turned on when the power cord is plugged in.
This equipment must be grounded.
The AC power input is Double-Pole Fused, also known as Neutral Fused, and requires this
equipment to be grounded as follows:
AC input - Connect to an electrical outlet provided with a protective ground connection.
DC input - Connect the protective ground to the designated external terminal on the
equipment rear panel.
This equipment has no internal user serviceable or replaceable parts.
The rear panel fuses and screw connection adapters are the only user replaceable parts. Use
only the original factory rated fuse types; otherwise safety of the equipment may be impaired.

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
5
Introduction
The ComSonics’ QAM Sniffer is a system which allows detection of CATV leakage in an all-
digital system without reserving any bandwidth for a discrete leakage carrier.
It is a CATV leakage detection system made up of two parts. The first part is a QAM Marker
Signal Source which is installed at a headend or hub of a CATV system. The second part is
the handheld/mobile QAM Sniffer unit or the GENACIS QS mobile unit.
The QAM Marker Signal Source, typically centered at 138 MHz or 612 MHz, uses a unique
modulation frequency for each CATV system to allow the QAM Sniffer units to detect leaks
only from the CATV system to which they are matched. The QAM Marker Signal Source can
be configured differently for up to three CATV systems in an overbuild area to distinguish
leaks between the CATV systems. The QAM Sniffer units must be configured to match the
appropriate QAM Marker Signal Source.
The QAM Sniffer unit is a handheld cable leakage detector with vehicle mounting capability.
It is an attractive and easy to use tool. Five buttons on the display panel and a multifunction
trigger type control, integrated into the handle, blend with the ergonomic contours of the
device. The buttons allow control of the settings needed in normal use, such as; power,
operational functions, backlight, and the loudness of our famous historic Sniffer warble tone.
The unit has a built-in folding dipole antenna for handheld use.
The GENACIS QS mobile unit is a GPS Enabled Automatic Cable Integrity System delivering
unmatched leakage location and management technology. It makes cable plant optimization
automatic and affordable. This hands free solution mounts easily in the cable operator’s
vehicles, detecting system leaks in real time as the technician performs their regular duties.
Leak intensity and location are recorded and uploaded by cell phone GPRS technology to the
central server allowing the cable operator to view their leaks, manage work orders and
monitor results. GENACIS QS gives the ability to proactively manage the cable plant to
optimize performance and customer satisfaction.
The QAM Sniffer and the GENACIS QS units use sophisticated methods to detect and
measure QAM Marker Signal Source leaks from the CATV system. They can differentiate a
true leak from general noise or signals originated by another marker in a co-located CATV
system.
The QAM Marker Signal Source can be configured through the internet using a standard web
browser. An Ethernet network internet connection is required.
Unpacking - The QAM Marker Signal Source and any ordered accessories are included in a
shipping container designed to provide the maximum protection during shipment. Upon receipt,
inspect the container and contents for signs of physical damage. Notify the freight forwarder of
any damage detected.
Please dispose of the cardboard packaging carefully and recycle where possible.
Power - The QAM Marker is powered by a standard AC detachable power cord.
Allow 15 seconds for the QAM Marker to initialize after applying power.

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
6
Components
Front Panel
The QAM Marker front panel has two indicators, a reset switch, and a marker selector. Refer to
Figure 1 for locations.
Figure 1 QAM Marker Front Panel Indicators and Controls
1. Power LED: Indicates unit is connected to and receiving 115 VAC or 48 VDC power.
2. Alarm LED: Indicates a marker output fault.
3. 612 LED: Indicates marker output frequency set to 612 MHz.
4. 138 LED: Indicates marker output frequency set to 138 MHz.
5. Reset Switch: Press to reset fault conditions when Alarm indicator is on OR when
directed during QAM Marker configuration.
6. Marker Identifier/Selector Switches: The standard marker setting is 1 for monitoring QAM
Marker Leakage signals. Using the Selector Switches the Marker output can be set to 1,
2, or 3. The QAM Sniffer Receivers in use in the field must be set to the same Marker
setting.
Back Panel
The QAM Marker back panel provides for power, control, and signal connections. Refer to Figure
2 for locations.
Figure 2 QAM Marker Back Panel
1. AC Power Connection with built in (internal) fuse: Accepts standard IEC power cord.
2. DC Power fuses (2 each): Provide protection for 48 VDC power (Optional).
3. *DC Power Connection: Optional Dual 48 VDC power input. Screw connection
adapter included.
4. Alarm Remote Connection: Connects to internal relay contacts to provide remote
monitoring. Screw connection adapter included.
5. LAN Connection: RJ45 Ethernet network connector for use during QAM Marker
configuration.
6. Ground Binding Post: Provides chassis ground point. Required if using DC Power.
7. Combined RF IN: Reference input for adjacent QAM signals combined with QAM
Marker output.
8. USB Connection: For factory calibration use only.
9. Marker Out Connection: QAM Marker output signal.
*NOTE: DC Power Connection is optional. Not available on all models. Contact ComSonics Technical
Support for additional information.

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
7
Headend/Hub Installation
Important!
For automatic mode operation at least one of the adjacent QAM signals from the applicable pair
(channel 16 or 17 for 138 MHz operation or channel 88 or 89 for 612 MHz operation) and the
QAM Marker signal must be present at the ‘Combined RF IN’ () before powering on the QAM
Marker unit. The QAM ‘Marker OUT’() is connected to a headend/hub combiner port.
The QAM Marker Signal Source uses 1 3/4 inches of rack space and should have free air space
of at least 1/2 inch above and to the ends of the chassis for ventilation. It needs power from the
AC () or DC () supply mains, a connection () to the headend/hub combiner network, and a
connection () to headend/hub signals at test point levels (consisting of at least the available
adjacent QAM channel/s and the QAM Marker signal).
Figure 3 Back Panel Connections
AC Power with built-in fuse - Accepts standard IEC power cord.
Refer to the Electrical Safety section on page 4.
*DC Power –Optional Dual 48 volt power, screw connection adapter
included.
Refer to the DC Powering section on the next page.
DC Power Fuse (2) - Protection for 48 volt power (Optional).
Alarm Remote - Connects to internal relay contacts, screw connection adapter included.
LAN - RJ45 Ethernet network connector.
Ground Binding Post - Chassis ground point.
Unit must be grounded if using DC Power.
Combined RF IN - Input for adjacent reference QAM signals with Marker signal.
USB - Service port, factory use only.
Marker OUT - QAM Marker signal output.
*NOTE: DC Power connection is optional. Not available on all models. Contact ComSonics
Technical Support for additional information.










+ A - + B -
48 VOLTS DC

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
8
DC Powering
Optional Dual 48 Volt DC Powering Recommendations.
Observe the following guidelines for using the 48 Volt DC Power option.
(DC power cables are not supplied with the equipment.)
Only use wiring rated to safely handle 48 VDC/0.5A.
Use the provided Phoenix 4-position pluggable terminal block
(Phoenix MSTB 2.5/4 - STF - 5.08).
Each terminal connection of the Phoenix plug can only accept one 24 to 12 AWG
stranded wire.
Do not exceed the rated capacity.
Use the shortest possible wire length.
Always use a continuous length of wire.
Do not splice wires to attain the needed length.
Use a larger wire size (within the recommended range of 24 AWG min to 12 AWG max)
to minimize voltage drops when wires must run a long distance.
Always use similar wire size for both the ‘+’ and the ‘-‘sections.
Use wire trays for routing where possible.
Avoid running wires near high energy or AC wiring.

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
9
Power and Alarm Indicators
Allow 15 seconds for the QAM Marker to initialize after applying power.
After initialization the front panel indicators will flash based on the current configuration. Refer to
Figure 4 for description of LED indications.
Figure 4 Front Panel LED Indications

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
10
Broadcast Insertion Considerations
For maintaining maximum plant-wide shielding effectiveness, the QAM Marker signal must be
available throughout the coaxial distribution network. For that reason, installation strategy is
important.
1. A single QAM Marker may serve, if the plant is configured to optically transport the broadcast
spectrum from a single location (the headend) with no further electrical conversion before
each fiber node.
2. Multiple QAM Marker units may be needed, if the headend optical output serves multiple hub
locations with recombined signaling or remapped channel plans. The QAM Marker output
signal must be combined with all other broadcast signals at the input to the final laser.
Directions in the document are based on the assumption that channels adjacent to the QAM
Marker (16 and 17 for 138 MHz operation and 88 and 89 for 612 MHz operation) are QAM
channels. If either of the adjacent channels is an analog carrier the QAM Marker must be
operated in manual mode. Manual mode configuration is covered later in this document.
In the automatic mode, the QAM Marker adjusts the marker signal level relative to the RMS
power level of an adjacent QAM channel. When the difference in power levels between the
adjacent QAM channels is less than 3 dB, the QAM Marker will use the channel with the lower
RMS power level as a reference. When the difference in power is greater than 3 dB, the QAM
Marker will use the channel with the higher power level as the reference.
The QAM Marker automatic leveling feature references on its Combined Input port the
simultaneous availability of the QAM Marker output signal, and either one or both QAM signals
adjacent to the selected output frequency. IMPORTANT: The Marker OUT port of the QAM
Marker is limited to ONLY the Marker test signal. The QAM Marker only references the
adjacent QAM signals and does NOT forward the payload of the adjacent QAM signals.
Where this combination (Marker output signal and either or both adjacent QAM signal) is
available at an open combiner port feeding the broadcast laser, or where that combination is
available on the laser output test point, the QAM Marker can be operated in the automatic
leveling mode. Note that the Combined Input port QAM signal level must be between -20 and
+30 dBmV. If the input levels are too low, an amplifier with an appropriate gain may be used and
if the input levels are too high, an attenuator may be used.
If the headend configuration cannot supply the required combination, it is quite likely that the
automatic leveling feature cannot be used and the QAM Marker output level will fall within the
unused laser output spectrum above the broadcast channels. The QAM Marker level must be set
manually based upon the nearest adjacent QAM signal amplitude.
The manual output range is -10 dBmV to +35 dBmV. After installation of the QAM Marker the
output level should be checked relative to the adjacent QAM channel levels at a convenient field
test point, such as a node electrical output. If the QAM Marker is not 30 dB (+0.0, -2.0 dB) below
the adjacent QAM signals the output should be adjusted. Care taken at the headend during initial
set-up will minimize any further adjustment.

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
11
The following table and text condenses and consolidates different headend/hub/node
configurations.
Type
Headend Output
Hub
Fiber Node
1
Optical
N/A
Optical > RF
2
Optical
Optical > Optical
Optical > RF
3
Optical
Optical > RF > Optical
Optical > RF
4
Optical
Optical > RF > Optical
Optical > RF
5
IP
IP > RF > Optical
Optical > RF
Type 1: Broadcast analog and QAM signals are combined at the headend location, fed to
one or more lasers and transported optically to one or more fiber nodes. A QAM Marker for each
frequency monitored operated in Automatic Leveling mode can be used for system-wide
distribution.
Type 2: Broadcast analog and QAM signals are combined at the headend location and
transported to one or more hub locations, then split and transported to one or more fiber nodes.
A single QAM Marker may serve system-wide distribution depending upon the combining
method. Operation in Automatic Leveling mode requires a single RF port with the presence of
both the inserted QAM Marker signal and either or both adjacent QAM channels. This may only
be available at the final laser output test point.
Type 3: Broadcast analog and QAM signals are partially combined at the headend location and
transported optically to one or more hub locations. At the hub location, the optical signals are
converted to RF and recombined with locally generated signaling or remapped to form a desired
channel plan. The new combination is supplied to the output laser and transported optically to
one or more fiber nodes. A single QAM Marker may serve system-wide distribution depending
upon the combining method. Operation in Automatic Leveling mode requires a single RF port
with the presence of both the inserted QAM Marker signal and either or both adjacent QAM
channels. This may only be available at the final laser output test point.
Type 4: Broadcast analog signals are combined for input to the broadcast laser and transported
to one or more hub locations. Digital baseband signals are streamed to hub locations on a high
speed fiber ring where they are recovered, converted to QAM, and combined with locally
generated signaling. A single QAM Marker may serve system-wide distribution depending upon
the combining method. Operation in Automatic Leveling mode requires a single RF port with the
presence of both the inserted QAM Marker signal and either or both adjacent QAM channels.
This may only be available at the final laser output test point.
Type 5: Individual hubs receive input in IP format from a central location. All RF signals (analog
and QAM) are generated and combined at each hub and transmitted optically to nodes. QAM
Marker(s) will be required at each hub. Operation in Automatic Leveling mode requires a single
RF port with the presence of both the inserted QAM Marker signal and either or both adjacent
QAM channels. This may only be available at the final laser output test point.

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
12
Configuration Manager Introduction (web based)
NOTE: Reference this section when performing the QAM Marker Manual Level Set Up
Procedure described in the following sections.
To configure the QAM Marker by direct connection, use a shielded cross-over type Cat 5
Ethernet cable between the computer and the LAN port on the back panel of the unit. Make sure
the computer’s Ethernet configuration has DHCP turned OFF. Use the option that allows the
user to enter in a manual IP Address such as “Use the following address”. Enter in an address
that does not conflict with the Marker address. A recommended address is: 192.168.0.49 Also
ensure the subnet mask is set to: 255.255.255.0. Remaining settings do not need to be altered.
To configure the QAM Marker on your existing network, connect it to a network switch or hub
using a shielded straight-through Cat 5 Ethernet cable. Make sure the QAM Marker default
address of 192.168.0.50 will not conflict in the existing network. If so, use the direct connection
method to change the unit address under Network Settings and then click on Apply Settings.
Once that operation completes, press the Reset button on the front panel.
Open a web browser and enter 192.168.0.50 (or the current IP address) in the address bar.
Recommended browsers are IE, Firefox, and Chrome. Note that the windows may appear
differently with different browsers. Reference Figure 5.
Figure 5 Authentication Window
Click “Log In” on the Authentication window to continue. The Authentication window varies per
operating system and web browser.
Leave the fields blank. The Authentication window shows the first time the unit is addressed as
long as the browser remains open.
The Home page (Figure 6) shows the QAM Marker’s Firmware Version, MAC Address, and the
Marker Configuration Manager Version. Menu items are available in the left column. Note: The
first time connecting to the QAM Marker an error screen may be shown. Click any of the tabs in
the left column to clear. This does not affect Marker operation.

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
13
Figure 6 Home Page
Network
Select “Network” from the left column menu bar to display the Network setting screen (Figure 7).
Figure 7 Network Settings Screen
If not connecting QAM Marker to a local network do not change default settings. If connecting to
local network, enter desired network information and click “OK”. Note this saves settings on page
but DOES NOT send settings to QAM Marker. Click Apply Settings to send the settings to the

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
14
QAM Marker unit.
Apply Settings
When the desired Network Settings are set click the OK button. This must be done as an
intermediate process. Once all settings are entered, click on Apply Settings in the left panel to
complete the process (Figure 8). The QAM Marker reboots and Configuration Manager returns to
the Home screen.
Figure 8 Apply Settings
Important:
When the Apply Settings function is used, the QAM Marker must be locally reset by
pressing the front panel Reset button. (This step must be done in order to access the Marker
Settings screen after the Apply Settings function is used.)
Marker
Click on “Marker” in the left column to access the Default Marker set up screen (Figure 9).
When the System Mode is set to Automatic, the Manual Level field is grayed out and not
available.
Figure 9 Default Marker Set Up

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
15
Enabling Manual in the System Mode allows entering an output level in the Manual Level field
(Figure 10).
Figure 10 Manual Level Set Up
The Marker Output can only be set to Off in the Manual mode. Selecting the Automatic mode
locks the Marker Output to On.
The Marker Frequency is set in MHz. Ranges are 136.5 to 138.5 MHz and 607 to 615 MHz.
Click the SEND button to immediately change the QAM Marker’s settings. No reboot is needed.
Note: If the Marker Frequency or the Manual Level is not within range, an invalid value warning
is shown.
If using Manual mode, the required marker level may be determined by a procedure in the next
section of this document. Enter the desired output in the Manual Level box and click Send to
immediately change the QAM Marker output. No reboot is needed.
The QAM Marker Identifier defaults to the front panel control. It may be changed using the Web
Interface by selecting the “Web Interface” option and selecting the desired Marker Identifier (1,2,
or 3). Changing the Front Panel Marker Identifier switch reverts control back to “Front Panel”.
Exit
Close the browser tab to exit the Configuration Manager. (No log-out function is needed.)

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
16
QAM Marker Manual Level Setup Procedure
Spectrum Analyzer
This section contains information to assist in the setup of the QAM Marker when configured to
operate in manual mode. Power measurements will be made on both the QAM television
channels in the CATV system and on the output from the QAM Marker unit itself.
A familiarity with the operation of the QAM Marker web-based user interface and operation of
a spectrum analyzer is required. The spectrum analyzer used for this document is an Agilent
N9342C. Other spectrum analyzers may have similar functions and settings.
Section 1 - QAM Power Measurements using a Spectrum Analyzer
When measuring signals having a bandwidth greater than that of the resolution bandwidth of the
instrument used to make the measurement, a measurement bandwidth correction factor must be
applied.
256-QAM television channels have a symbol rate of 5.361 million symbols per second for a 6
MHz bandwidth and 6.952 million symbols per second for a 8 MHz bandwidth. This corresponds
to a Signal Bandwidth (SBW) of 5.361 MHz and 6.952 MHz respectively.
A Spectrum Analyzer has a number of Resolution Bandwidth (RBW) settings. The setting
selected when measuring power must be used to calculate the Bandwidth Correction factor.
This is because the amount of power measured on the Spectrum Analyzer is restricted to the
resolution bandwidth (RBW), thus it must be adjusted to obtain the correct measurement.
The Bandwidth Correction factor (BWC) is calculated with the following equation:

BWC (in dB)10 *Log10 SBW (in MHz)
RWB (in MHz)


 


When using Quadrature Amplitude Modulation, the signal produced has characteristics of noise.
When measuring signals ‘noise like’ in nature and averaging the resulting logarithmic output on
the screen of a spectrum analyzer, an under-response of 2.51 dB is incurred. To compensate,
add 2.51 dB to the measurement obtained, altering the formula to:

BWC (in dB)10 *Log10 SBW (in MHz)
RWB (in MHz)


 


2.51 dB
It is possible that the spectrum analyzer uses an FFT type detector to make the power
measurement. In this case, the 2.51 dB correction does NOT apply. The correction is only for
the case where a log-type detector, usually called “sweep”, is used to measure signals “noise-
like” in nature, such as QAMs.

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
17
The instructions contained in this document for the spectrum analyzer control are specifically
for the Agilent N9342 (Figure 11), however many of the menu/command structures from
spectrum analyzer to spectrum analyzer are similar.
Figure 11 Spectrum Analyzer
The key functions used for the measurements in this document are as follows:
SPAN controls the amount of bandwidth shown on the display indicated and/or set by the
start, center, and stop frequency.
RBW (Resolution Bandwidth) is an important function. It is a band pass filter before the
power measurement is taken. It impacts the measurement in three important ways:
1) The measured power at the marker point is constrained to the band pass limits,
2) the noise floor decreases as the band pass range is narrowed, and
3) frequency signals close together (the QAM Marker is a good example) cannot be
resolved unless the RBW is set low enough to discriminate between them.
VBW (Video Bandwidth) determines the capability to discriminate between two different
power levels. A narrower VBW setting removes more noise in the detector output and
‘smooths’the envelope display. Set the VBW to be 3x RBW for QAM Marker measurements.
Sweep mode has a lower RBW of 1 kHz. For a lower RBW, set the sweep mode to ‘FFT’ or
‘Auto’. Auto mode changes settings as needed.
Span:
Start
Center
Stop
BW:
RBW
VBW
Amptd:
Y-Axis
Ref. Level
Scale
dB/Division
Peak
Marker
Sweep:
Auto
Sweep
FFT

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
18
Section 2 - Measuring the QAM Channel Power Level
Use the following steps to measure and calculate the total QAM Power Level:
1) Set the spectrum analyzer to a 15 MHz span centered at the Marker Frequency to be used
(138 MHz or 612 MHz). This should be a resolution bandwidth (RBW) of 100 kHz (30 kHz for
FFT mode). Set the video bandwidth filter (VBW) bandwidth at least three times the RBW.
The VBW setting is expressed as a ratio to the RBW; i.e. 3:1. These settings appear on the
bottom of the display as RBW and VBW. For a 15 MHz span, use the SPAN and BW
functions. Adjust the Reference level and the Amplitude scale, if needed, using Amptd
function.
2) Enable trace averaging mode and adjust to collect 100 samples. Wait a few seconds for the
display to stabilize. The two QAM signals adjacent to the desired frequency should be within
1 dB of each other. Record the power level of the QAM channel having the lower level as
indicated on the spectrum analyzer. In Figure 12, the QAM power is measured at 16.02
dBmV. Use the Trace function to set averaging. Use the ‘more’ menu under Trace.
Figure 12 Measuring Adjacent QAM Channels
3) Calculate the bandwidth correction factor based on the resolution bandwidth (RBW) selected
on the spectrum (100 kHz). BWC = 10 * Log10 (5.361 / 0.1) = 17.29 dB (for 6 MHz QAM).
4) Add the measurement bandwidth correction factor of 17.29 dB to the number obtained in
step 2: 16.02 + 17.29 = 33.31 dBmV.

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
19
5) The logarithmic output is averaged on the display and the correction factor of 2.51 dB must
be applied. For this example: 33.31 dBmV + 2.51 dB = QAM Power Level of 35.82 dBmV.
Section 3 - Calculate the Required QAM Marker Power Level
The total marker power is set to a level 30 dB less (± 0.5 dB) than the calculated total QAM
power level.
Example: Total QAM Power Level calculated: 35.82 dBmV. Subtract 30 dB and set the marker
power to this level. 35.82 dBmV - 30 dB = 5.82 dBmV (± 0.5 dB)
Section 4 - Measuring the QAM Marker Power
1) The QAM Marker Signal is comprised of a signal in a double sideband, suppressed carrier,
modulation scheme.
2) Set the spectrum analyzer to a 5 kHz span centered at the QAM Marker output frequency.
For best results, use a RBW setting between 1 kHz and 30 Hz with 100Hz or 30Hz providing
the best results. Disable the trace averaging mode.
3) As illustrated in Figure 13, the two marker sidebands and perhaps some leakage of the
suppressed carrier at the center frequency will be visible on the spectrum. Use the peak
search function to measure the power level of one of the sidebands (they both should be
equal) and add 3 dB to this value for the total marker power. In this example: 2.82 dBmV + 3
dB = 5.82 dBmV. If the spectrum analyzer does not have a RBW small enough to resolve
the two sidebands, you will see a single ‘haystack’ type trace. In this case, all of the marker
power is indicated by the single trace and the 3 dB correction factor is not applied.

QAM Marker
Signal Source
rev1.0.2 June 20, 2014
20
Figure 13 Measuring QAM Marker Output
4) If the spectrum has a selectable Sweep/FFT mode, the resolution bandwidth may be further
reduced by selecting the FFT mode. The result in Figure 14 is still at a 5 kHz span but at a
RBW of 30Hz. Important to note, the indicated level of 2.31 dBmV is less than measured at
the previous RBW setting. This is an artifact of the measuring process. More accurate results
are obtained if the span is set to a lower value thus increasing the number of data points
used to represent the signal on the screen, refer to Figure 14. FFT mode is set using the
Sweep function. If the sweep mode is set to ‘Auto’ this self-adjusts.
In the event a single sideband of the QAM
Marker is used to measure the marker power
level, add an extra 3 dB in the calculation to
account for total power. In this example, the total
marker power would be 2.82 dBmV + 3 dB =
5.82 dBmV