Insertion Loss Measurement Methods Application

Insertion Loss Measurement Methods Application
APPLICATION NOTE
Insertion Loss
Measurement Methods
SITE MASTER™
Introduction
Transmission feed line system performance plays an important
role in wireless network coverage. Insertion loss measurement
is one of the critical measurements used to analyze transmission
feed line installation and performance quality. This application
note explains how Site Master is used to measure cable insertion
loss with different test methods and how to predict the maximum allowable cable insertion loss through manual calculations.
In wireless communication systems, the transmit and receive
antennas are connected to the radio through coaxial cable
and/or waveguide transmission lines (Figure 1).
Insertion loss measures the energy absorbed by the transmission
line in the direction of the signal path in dB/meter or dB/feet.
Transmission line losses are dependent on cable type, operating
frequency and the length of the cable run. Insertion loss of a
cable varies with frequency; the higher the frequency, the
greater the loss.
Insertion loss measurements help troubleshoot the network
by verifying the cable installation and cable performance.
High insertion loss in the feedline or jumpers can contribute
to poor system performance and loss of coverage. Measuring
insertion loss using Site Master assures accurate and repeatable
measurements.
Verify Cable Insertion Loss
From Ground Level
Antenna
Jumper
Main Feeder
Antenna
Jumper
Connectors
Figure 1. Typical transmission line system
Measurement Methods
During network deployment, maintenance, and trouble shooting phases,
insertion loss can be measured by disconnecting the antenna and connecting
an enclosed short at the end of the
transmission line. If a Tower Mounted
Amplifier (TMA) is used in the transmission feed line system, it is best to remove
the TMA and antenna from the system
configuration to perform an insertion
loss measurement. It is best to always disconnect the cable at the same location
so the measured data can be compared
to the historical data for accuracy and
repeatability.
Using Site Master, cable insertion loss
can be measured in CABLE LOSS or
RETURN LOSS mode. In Cable Loss
mode, Site Master automatically considers the signal traveling in both directions
thus making the measurement easier for
the user in the field.
The following section explains the procedure to measure insertion loss in cable
loss mode and return loss mode. The
measurement setup and equipment
required is the same for both modes.
Application Note
Measuring
Insertion Loss
Using CABLE
LOSS MODE
Required Equipment
• Site Master Model S11xx,
S33xx, or S251x
• Precision Open/Short,
Anritsu 22N50 or
Precision
Open/Short/Load, Anritsu
OSLN50LF
Insertion Loss Measurement
Setup
The insertion loss measurement set up
for a typical transmission feed line
system is shown in Figure 2. Remove
the antenna and connect an enclosed
precision “short” at the end of the
transmission line.
If a Tower Mounted Amplifier (TMA)
is in the transmission feed line system,
remove the TMA and antenna and
connect an enclosed short at the end
of the transmission line. Insertion loss
measurement for a transmission feed
line system with a tower mounted
amplifier is shown in Figure 3.
• Precision Load, Anritsu
SM/PL
Antenna
Removed
• Test Port Extension Cable,
Anritsu 15NNF50-1.5C
• Optional 510-90 Adapter,
DC to 7.5 GHz, 50 Ω,
7/16(f)-N(m)
Test Port
Cable
Jumper
Main Feeder
Antenna
Jumper
Precision
Short
Site Master S251C
ESCAPE
1
2
START
CAL
CLEAR
AUTO
SCALE
3
4
SAVE
SETUP
RECALL
SETUP
5
6
LIMIT
MARKER
ENTER
7
8
SAVE
DISPLAY
RECALL
DISPLAY
FREQ/DIST
AMPLITUDE
RUN
HOLD
0
9
+/-
PRINT
ON
OFF
MODE
SYS
.
SWEEP
Figure 2. An insertion loss measurement setup after antenna
is removed.
Antenna
Removed
TMA
Removed
Test Port
Cable
Jumper
Main Feeder
TMA
Jumper
Antenna
Jumper
Tx/Rx
Precision
Short
Site Master S251C
ESCAPE
1
START
CAL
3
SAVE
SETUP
5
LIMIT
2
CLEAR
AUTO
SCALE
4
Step 4. Connect the phase stable test
port extension cable to the
RF port.
Step 5. Calibrate the Site Master at the
end of the phase stable test port
extension cable. (See the
section entitled “Calibrating
Site Master with the Phase
Stable Test Port Extension
Cable” for details.)
Step 6. Disconnect the antenna and
connect an enclosed precision
"short" at the end of the
transmission line.
Step 7. Connect the other end of the
transmission line to the phase
stable cable of the Site Master.
A trace will be displayed on the
screen when the Site Master is
in continuous sweep mode.
Step 8. Press the AMPLITUDE key and
set the TOP and BOTTOM
values of the display. In Figure
4, the TOP is set to 2 dB, and
the BOTTOM is set to 5 dB.
Step 9. Press the MARKER key.
Step 10.Set M1 to MARKER TO PEAK.
Step 11.Set M2 to MARKER TO VALLEY.
Step 12.Calculate the insertion loss by
averaging M1 (MARKER TO
PEAK) and M2 (MARKER TO
VALLEY) values as follows:
RECALL
SETUP
6
MARKER
ENTER
7
SAVE
DISPLAY
9
ON
OFF
MODE
FREQ/DIST
AMPLITUDE
8
RECALL
DISPLAY
0
RUN
HOLD
+/-
PRINT
SYS
.
SWEEP
Insertion Loss = (M1 dB + M2 dB)
Figure 3. Insertion loss measurement setup when TMA
is in line.
2
= 3.23 + 3.95 = 3.59 dB
2
Procedure
Step 1. Power On the Site Master and
press the MODE key.
Step 2. Select FREQ-CABLE LOSS using
the Up/Down arrow key and
press ENTER.
Step 3. Set the start and stop frequencies F1 and F2. As an example,
F1=750 MHz and F2=850 MHz
for a typical cellular frequency
band.
2
Step 13. Press SAVE DISPLAY and name
the trace using the soft keys
and press ENTER.Saving the
display is recommended for
historical documentation.
Saved traces can be used in
the future to compare, check
or verify changes in the transmission feedline performance.
Application Note
Step 7. Connect the other end of the transmission
line to the phase stable cable of the Site
Master. A trace will be displayed on the
screen when the Site Master is in continuous
sweep mode.
Step 8. Press the AMPLITUDE key and set the TOP
and BOTTOM values of the display. In
Figure 5, the TOP is set to 4 dB, and the
BOTTOM is set to 10 dB.
Step 9. Press the MARKER key.
Step 10.Set M1 to MARKER TO PEAK.
Step 11.Set M2 to MARKER TO VALLEY.
Step 12.Calculate the insertion loss by averaging M1
(MARKER TO PEAK) and M2 (MARKER
TO VALLEY) values and dividing by two as
follows:
CL - CABLE LOSS
CAL ON
2.00 dB
LIM ON
517 POINTS
RECALL
M1
M2
M3
M4
M5
5.00 dB
750 dB
M1:3.23,750.4 MHz
M2:3.95,848.4 MHz
FREQ (MHz)
M3=OFF
M4=OFF
850.0
M6
Figure 4. Typical Insertion Loss Display in Cable Loss Mode.
M1 dB + M2 dB
In Cable Loss mode, the Site Master automatically considers
the signal path in both directions when calculating the cable
insertion loss. As such, Cable Loss mode is recommended
when making cable insertion loss measurements.
Insertion Loss =
2
2
6.47 + 7.89
=
RL - RETURN LOSS
CAL ON LIM ON
4.00 dB
517 POINTS
RECALL
2
2
M1
= 3.59 dB
M2
Step 13.Press SAVE DISPLAY and name the trace
using the soft keys and press ENTER.
M3
Calibrating Site Master with
the Phase Stable Test Port
Extension Cable
M4
M5
10.00 dB
750 dB
M1:6.47,750.4 MHz
M2:7.89,848.4 MHz
FREQ (MHz)
M3=OFF
M4=OFF
850.0
M6
Figure 5. Typical Insertion Loss Display in Return Loss Mode
Measuring Insertion Loss
using RETURN LOSS MODE
Step 1. Power on the Site Master and press the
MODE key.
Step 2. Select the FREQ-RETURN LOSS using the
Up/Down arrow key and press ENTER.
Step 3. Set the start and stop frequencies F1 and F2.
As an example, F1=750 MHz and F2=850
MHz for a typical cellular frequency band.
Step 4. Connect the phase stable test port extension
cable to the RF port.
Step 5. Calibrate the Site Master at the end of
the phase stable test port extension cable.
(See the section entitled “Calibrating Site
Master with the Phase Stable Test Port
Extension Cable” for details.)
Step 6. Disconnect the antenna and connect an
enclosed precision "short" at the end of
the transmission line.
3
The phase stable test port extension cable is used as
an extension cable to the test port of the Site Master,
and ensures accurate and repeatable measurements.
The phase stable cable can be moved and bent while
making a measurement without causing errors in the
measurement. When poor quality cables are used
as an extension test port cable, large error will be
introduced in the measurements when the cable
is moved.
For accurate results, Site Master should be calibrated
at the ambient temperature before making any
measurements. The Site Master must be re-calibrated
whenever the setup frequency changes, the temperature exceeds the calibration temperature window
or when the test port extension cable is removed
or replaced.
Connect the phase stable test port extension cable to
the Site Master RF Port. The Site Master with phase
stable cable combination can be calibrated manually
using Open, Short and Load (OSL) precision
components (Figure 6), or by using the InstaCal®
module. Manual calibration is explained here. For
the InstaCal procedure, refer to the Site Master
user guide.
Note: The InstaCal module is not compatible with the
Site Master S251C Model.
Application Note
Open
Short
Calibration
Load
Test Port Cable (Optional)
Figure. Calibrating at
the end of the Phase
Stable Test Port
Extension Cable.
For example:
Cable
Type
Cable
Attenuati
on (dB/ft)
Bottom
Jumper
LDF4-50A
0.0204
X
20
=
0.408
Main
Cable
LDF5-50A
0.0115
X
200
=
2.30
Top
Jumper
LDF4-50A
0.0204
X
10
=
0.204
RF Out/Reflection
Test Port
Site Master S331C
ESCAPE
1
START
CAL
3
SAVE
SETUP
5
LIMIT
2
CLEAR
AUTO
SCALE
4
RECALL
SETUP
6
MARKER
ENTER
7
8
SAVE
DISPLAY
RECALL
DISPLAY
9
0
ON
OFF
MODE
FREQ/DIST
AMPLITUDE
RUN
HOLD
+/-
PRINT
SYS
.
SWEEP
Site Master S11xx/S33xx/S251x
Note: For Cable Loss-One Port
measurements, Site Master S251C
requires only one port calibration.
Note: If the phase stable cable is
removed from the test port, the
calibration is not valid.
Number of
Connector Pairs
Manual Calibration Procedure
Step 1. Power on the Site Master.
Step 2. Select the appropriate frequency range.
Step 3. Connect the phase stable test port extension cable to
the RF port.
Step 4. Press the START CAL key. The message "Connect Open to
RF OUT port or connect InstaCal module and press ENTER"
will appear in the display.
Step 5. Connect the OPEN precision calibration component
to the end of the test port extension cable. Press the ENTER
Key.
Step 6. The message "Measuring OPEN" will appear, and after the
measurement "Connect SHORT to RF OUT" will appear.
Step 7. Remove the “open” and connect the “short” precision calibration component to the test port extension cable.
Press the ENTER key.
Step 8. The message "Measuring SHORT" will appear, and after the
measurement "Connect TERMINATION to RF OUT" will
appear.
Step 9. Remove the “short” and connect the “precision termination”
at the end of the test port extension cable. Press the ENTER
key.
Step 10.The message "Measuring TERMINATION" will appear. After
the measurement, the “CAL OFF” message will change to
"CAL ON" on the upper left-hand corner of the display.
Step 11.Remove the precision termination from the text port
extension cable.
Calculating Transmission Line Insertion Loss
Cables have different insertion losses at different frequencies.
For example LDF4-40A attenuation at 1 GHz is 0.022 dB/ft
(0.073 dB/m) and at 2 GHz it is 0.0325 dB/ft (0.107 dB/m).
As the frequency increases or the length of the cable run increases,
the amount of cable insertion loss increases.
To verify cable insertion loss measurements are reasonable, the
expected insertion loss can be calculated manually using the
following procedure:
• Calculate the estimated worst loss of each component in the
transmission line system.
• Add all the component’s estimated worst losses together to
calculate total insertion loss in the transmission line system.
SALES CENTERS:
United States (800) ANRITSU
Canada (800) ANRITSU
South America 55 (21) 286-9141
Europe 44 (0) 1582-433433
Japan 81 (03) 3446-1111
Asia-Pacific 65-2822400
4
Cable
Length
Loss per Pair
in dB
X
0.28
Insertion
Loss (dB)
Total Connector
Loss (dB)
=
1.12
Insertion loss of the = Bottom Jumper Loss
transmission system + Main Cable Loss
+ Top Jumper Loss
+ Connector Losses
= 0.408 + 2.3 +0.204 +1.12
= 4.03 dB
Compare the measured insertion loss to
the calculated insertion loss to verify
transmission line performance. The
measured cable insertion loss should be
lower than the calculated cable insertion loss.
Summary
The preferred method to measure
Cable Insertion Loss using Site Master
is Cable Loss mode. Cable loss mode
automatically considers the signal
traveling in both directions and thus
makes it easier to measure the cable
insertion loss in the field. Measured
Insertion Loss should always be compared to the calculated loss to verify
accuracy thus assuring transmission line
performance. The calculated insertion
loss is usually a “worst case scenario”.
Cable insertion loss may be difficult to
measure on excessivly long or highly
lossy cables. When the cable insertion
loss is greater than 20 dB, it will be hard
to measure.
All trademarks used are the property of their
respective owners.
Microwave Measurements Division
490 Jarvis Drive, Morgan Hill, CA 95037-2809
http://www.us.anritsu.com
11410-00276 Rev. A, ©Anritsu March 2003, Data subject to change without notice
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