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Belden 50 Ohm Coaxial Testing
Carl W. Dole, Product Engineer
October 23, 2003
Purpo:
This short paper describes the common practice ud at the Belden Engineering Center to measure certain coaxial cable attributes. Specifically, 6 GHz Belden Wireless 50 Ohm Coaxial Cable.
VSWR
Equipment: Agilent 8753ES network analyzer with option 010
Hewlett-Packard 85032B calibration kit (type N, 50 ohm)
Equipment Setup:
1. Setup one port of the network analyzer with a type N female 50-ohm connection. Connect a 50-ohm extension cable to
the other port so that it has a type N male 50-ohm connection at its open end. This cable will remain connected for all calibration and testing. Connect the open male end of the extension cable to the female connection of the other port to create a through connection between the two ports.
2. Set the network analyzer ttings as follows:
Start frequency: 5 MHz
Stop frequency: 6 GHz
Sweep type: Log Freq
Number of points: 1601
Sweep time: 5 conds
IF bandwidth: 1 kHz
Gate start: 3 nanoconds
Gate stop: 230 nanoconds
Gate shape: normal
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3. Press the Set Freq Low-Pass button in the calibration menu of the network analyzer. This will change the start and stop
frequencies to approximately 3.75 MHz and 5999.99 MHz, respectively. This is required for the u of the gating function later.
4. Select the calibration kit option in the network analyzer menu that matches the model number of the calibration kit
actually ud.
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5. Perform a full two-port calibration of the analyzer at the male-female connection performed above.
Sample preparation:
1. U a sample length of 100 feet.
2. Install a type N male connector on one end of the sample.
3. Install a type N female connector on the other end of the sample.
Note: Cable preparation and connector asmbly is CRITICAL to the evaluation and performance of the cable asmbly.
Poorly installed connectors may result in misleading data and indicate the entire cable asmbly as being defective when, in fact, it may be a cable/connector interface issue. Consult connector manufacturer’s termination
instructions for details. Turning on the gating function is ud to help eliminate the connector effect and measure only the cable in the asmbly. The difference between the gating on and gating off measurement values is due to the connector and/or asmbly termination quality. Select the gate start and stop times bad upon the sample
length. This t-up assumes a 100ft sample (asmbly) of cable under test with a velocity of propagation 86%.
Sample test:
1. Connect the prepared sample where the calibration was performed. The sample under test is in s
eries with the
extension cable and creates a through connection between the two ports.
2. Initiate the analyzer sweep if it is not already sweeping.怎样除蟑螂
3. Select S11 and t the display mode to VSWR to view the sample end connected to port 1. Select S22 and t the display
mode to VSWR to view the other end of the sample.
4. Obrve the VSWR display with the gate function off. High VSWR due to poor connectors and/or connector
installation is generally indicated by VSWR that slopes upward as the frequency increas. Reinstall the connectors or install better quality connectors if necessary.
5. Turn the gate function on.
6. Record the data.
Attenuation
1. U the same equipment, tup, calibration, and cable sample as for VSWR.
2. Turn the gate function off.
3. Select S21 or S12 and a display mode of log magnitude to view the attenuation.
4. Record the data.
5. Convert the data to decibels per 100 feet.
TDR Impedance
Equipment: Tektronix 11801C digital sampling oscilloscope with SD-24 TDR/sampling head
50-ohm air line
Equipment Setup:
Connect the air line to one channel of the TDR/sampling head using a piece of 50-ohm coaxial cable.
Sample test:
1. Connect the sample to test to the open end of the air line. The sample can be the same as ud for VSWR and
attenuation.
2. Measure the TDR impedance.
Capacitance at 1 kHz
Impedance/Gain-Pha Analyzer
Equipment: Hewlett-Packard越南美食
4194A
Four-port to two-terminal adapter
Equipment Setup:
1. Connect the four-port to two-terminal adapter to the four impedance terminals of the analyzer.
2. Set the analyzer as follows:
Center frequency: 1 kHz
Frequency span: 1 kHz
Number of points: 11
Cp-Q
Function: Impedance,
A display: On
B display: Off
3. Perform an open/short calibration of the analyzer
Sample test:
1. Connect the sample to test to the two terminals of the adapter. The sample can be the same as ud for the previous
tests.
2. Record the capacitance.
3. Calculate the capacitance in picofarads per foot.
Inductance at 1 MHz
Impedance/Gain-Pha Analyzer
Equipment: Hewlett-Packard
4194A
Four-port to two-terminal adapter
Equipment Setup:
1. Connect the four-port to two-terminal adapter to the four impedance terminals of the analyzer.
2. Set the analyzer as follows:
Center frequency: 1 MHz
Frequency span: 1 kHz
Number of points: 11
Function: Impedance,
Ls-Q
A display: On
B display: Off
3. Perform an open/short calibration of the analyzer
Sample test:
1. Connect the sample to test to the two terminals of the adapter. Short the far end of the cable. The electrical length of
the sample should be 1/8 wavelength or less.
2. Record the inductance.
3. Calculate the inductance in nanohenries per foot.
Velocity of Propagation
Equipment: Hewlett-Packard 8751A Network Analyzer
Equipment Setup:
1. Set up the analyzer as follows:
Start frequency: 100 MHz职业技能鉴定资格证书查询系统
Stop frequency: 250 MHz
Number of points: 401
IF bandwidth: 1 kHz适合男生看的小说
Sweep time: 1 cond
Measure: Input
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Mode:
Continuous
Sweep
2. Connect a coaxial tee between the RF OUTPUT and input R of the analyzer
Sample test:
1. Connect a 15 to 20 foot sample of the cable to the open port of the tee. Leave the other end of the sample open circuit.
2. Measure the sample length from the center of the tee to the open end of the sample. U this length in the velocity
calculations.
3. Record the frequencies of three concutive resonance points above 100 MHz. The resonant points are the troughs in
the trace.
4. Change the analyzer frequency span to 1 MHz. Change the analyzer center frequency to each of the frequencies
recorded above to obtain a more accurate measurement of the frequencies. U the marker minimum function to locate the bottom of each trough. Record the more accurate frequencies and u in the calculations below.
5. Calculate the velocity of propagation at each of the three frequencies per MIL-C-17G ction
6.5.3. The three
velocities should be within 1% of each other. Average the three velocities and report this as the sample velocity of propagation.
