Before you send your test equipment to be calibrated or repaired, you may want to check the weakest link— the cables and connectors to make sure they are not affecting your test equipment’s performance. High quality cables are expensive and may cost $2,000 and up to replace. We recommend sending cables along with your equipment to insure that equipment and cables are checked for damage.
Cables and connectors are used to carry data/signals from an antenna to a receiver (satellite, television, radio) in a range of consumer devices, military equipment, and ultra-sound scanning equipment. RF cables and connectors are high precision test assemblies, which along with a calibration kit, adapters, and a torque wrench, ensure the accuracy and signal integrity when measured by vector network analyzers. Issues affecting RF cables and connectors performance include unwanted signals caused by signal leakage, interference, and noise. To avoid these common issues, the best way to insure optimum performance is to check for wear and tear of cables, metal shavings, and dirt that may risk damaging equipment due to using faulty cables and connectors. The ideal cable transfers maximum RF energy with the minimum amount of loss possible. Factors for choosing the best cable for a test solution include:
- Operating Frequency
- Characteristic Impedance
- Insertion Loss
- Return Loss/VSWR
- Power handling capacity
- Operating temperature
- Flexibility
- Size
- Weight
- Shielding and ruggedness
- Cost: Primary trade-off
Figure 1. Visual signs of misused or worn out cables
Visual Inspection
Check and make sure there is no visible damage or debris in the connector interfaces. Look for concentricity in the center pins.
Inspecting Interfaces
Check for signs of damage including scoring or dents on outer conductor, center pins, and dielectric surfaces. Center contacts should be present, straight, and centered. The contact pin should not be loose or cross-threaded. Contact shoulders should be sharply defined with flat edges and no rolled or mushroomed edges. If there are signs of damage, cables should not be used.
Interface Thread Inspection
Make sure there are no signs of cross-threading or broken or missing threads. Do not connect them with any connector or interface gauge if there are signs of damage.
Interface Cleaning
Use a clean, soft, lint-free swab, like a cotton swab, lightly moistened with isopropyl alcohol to remove dirt, dust, and other debris.
- Clean the connector threads. Make sure alcohol does not come into contact with the dielectrics or gaskets; this can cause VSWR, phase or insertion loss problems.
- Allow the isopropyl alcohol to evaporate. Dry threads with containerized compressed air. Make sure connectors are dry and free of visible debris before use.
Interface Gauging
Start with clean interfaces that meet specifications for pin depths (see Table 1). For preventative maintenance, have connectors gauged periodically on a fixed schedule set for every 100 mating cycles or every week. Make sure gages are calibrated. Following these procedures will insure that cables and connectors will not damage interfaces, including test ports.
Interface gages are important to measure pin depths and to make sure pin depths do not have excessive recession or protrusion, but they only provide rough measurements. Plug gages provide more measurement uncertainty than threaded gages. See Table for interface reference planes.
Table 1: Connector Interfaces and Tolerances
| Connector Interface | Reference Plane Recession, in (mm) | Specification |
| 1.0mm female | 0.000 / -‐0.002 | IEEE STD 287 |
| (0.000 / -‐0.051) | ||
| 1.0mm male | 0.000 / -‐0.002 | IEEE STD 287 |
| (0.000 / -‐0.051) | ||
| 1.0mm port female | 0.000 / -‐0.002 | IEEE STD 287 |
| (0.000 / -‐0.051) | ||
| 1.0mm port male | 0.000 / -‐0.002 | IEEE STD 287 |
| (0.000 / -‐0.051) | ||
| 1.85mm female | 0.000 / -‐0.002 | IEEE STD 287 |
| (0.000 / -‐0.051) | ||
| 1.85mm male | 0.000 / -‐0.002 | IEEE STD 287 |
| (0.000 / -‐0.051) | ||
| 1.85mm port female | 0.000 / -‐0.002 | IEEE STD 287 |
| (0.000 / -‐0.051) | ||
| 1.85mm port male | 0.000 / -‐0.002 | IEEE STD 287 |
| (0.000 / -‐0.051) | ||
| 2.4mm female | 0.000 / -‐0.001 | IEEE STD 287 |
| (0.000 / -‐0.025) | ||
| 2.4mm male | 0.000 / -‐0.0025 | IEEE STD 287 |
| (0.000 / 0.0635) | ||
| 2.4mm port female | -‐.0001 / -‐0.001 | IEEE STD 287 |
| (-‐.0025 / -‐.0254) | ||
| 2.4mm port male | -‐.0001 / -‐0.001 | IEEE STD 287 |
| (-‐.0025 / -‐.0254) | ||
| 2.92mm female | 0.000 / -‐0.003 | IEEE STD 287 |
| (0.000 / -‐0.076) | ||
| 2.92mm male | 0.000 / -‐0.003 | IEEE STD 287 |
| (0.000 / -‐0.076) | ||
| 2.92mm port female | 0.000 / -‐0.003 | IEEE STD 287 |
| (0.000 / -‐0.076) | ||
| 2.92mm port male | 0.000 / -‐0.003 | IEEE STD 287 |
| (0.000 / -‐0.076) | ||
| 3.5mm female | 0.000 / -‐0.003 | IEEE STD 287 |
| (0.000 / -‐0.076) | ||
| 3.5mm male | 0.000 / -‐0.003 | IEEE STD 287 |
| (0.000 / -‐0.076) | ||
| 3.5mm port female | 0.000 / -‐0.003 | IEEE STD 287 |
| (0.000 / -‐0.076) | ||
| 3.5mm port male | 0.000 / -‐0.003 | IEEE STD 287 |
| (0.000 / -‐0.076) | ||
| 4.3-‐10 female | -‐0.122 / -‐0.138 | IEC 60169-‐54 |
| (-‐3.099 / -‐3.505) | ||
| 4.3-‐10 male | +0.305 / -‐0.315 | IEC 60169-‐54 |
| (+7.747 / -‐8.001) | ||
| 7-‐16 female | -‐0.069 / -‐0.082 | IEC 60169-‐4 |
| (-‐1.753 / -‐2.083) | ||
| 7-‐16 male | 0.84057971 | IEC 60169-‐4 |
| (+1.471 / +1.770) | ||
| 7mm | -‐0.002 / +0.002 | IEEE STD 287 |
| (-‐0.051 / +0.051) | ||
| BNC female | 0.902912621 | MIL-‐STD-‐348 |
| (+4.724 / +5.232) | ||
| BNC male | -‐0.210 / -‐0.230 | MIL-‐STD-‐348 |
| (-‐5.334 / -‐5.842) | ||
| C female | +0.309 max. | MIL-‐STD-‐348 |
| (+7.849) | ||
| C male | 0.75 | MIL-‐STD-‐348 |
| (+0.762 / +1.016) | ||
| F female | +0.200 max. | ANSI/SCTE 01 2015 |
| (+5.080) | ||
| F male | 0.666666667 | ANSI/SCTE 124 2015 |
| (+6.350 / +9.525) | ||
| N Female | 0.903381643 | MIL-‐STD-‐348 |
| (+4.749 / +5.258) | ||
| N Male | +0.210 / -‐0.230 | MIL-‐STD-‐348 |
| (+5.334 / -‐5.842) | ||
| SMA female | 0.000 / 0.010 | MIL-‐STD-‐345 |
| (0.000 / +0.254) | ||
| SMA male | 0.000 / -‐0.010 | MIL-‐STD-‐348 |
| (0.000 / -‐0.254) | ||
| TNC female | 0.902912621 | MIL-‐STD-‐348 |
| (+4.724 / +5.232) | ||
| TNC male | -‐0.210 / -‐0.230 | MIL-‐STD-‐348 |
| (-‐5.334 / -‐5.842) |
* Generally the tolerance for pin protrusion is 0.000.
Cable Assembly Mating
Interface Alignment
Contact pins and dielectrics can be damaged if misaligned connectors are mated. Check mating interfaces for parallel and on-center connections prior to and during mating cycles.
Figure 2. RF SMA (f) to SMA (m) cables
Figure 3. APC-7 testing cables
Interface Rotation
If connectors rotate during mating cycles, both the outer conductor and center contact can be damaged. Hold the connector steady using a flat wrench on the connector. Use a proper torque wrench during mating cycles.
Recommended Mating Torque
Improper torque use can cause inaccurate measurements and over-torque coupling can damage test devices, adaptors, and test ports. For all mating cycles, calibrated torque wrenches should be used. Make sure the correct torque value is used when mating a specific connector type. Using a torque wrench helps insure consistency between measurements. For connectors and cables, break over torque wrenches are recommended. See table below for recommended coupling torque.
Table 2: Recommended Coupling Torque
| Interface type | Coupling torque, in-‐lbs. (N-‐m) |
| 1.0mm | 4 (0.45) |
| 3.5mm, 2.92mm, 2.4mm, 1.85mm | 8 (0.90) |
| TNC | 5 (0.57) |
| SMA (Brass) | 5 (0.57) |
| SMA (Stainless) | 8 (0.90) |
| 7mm, N | 12 (1.36) |
| F | 15 (1.70) |
| C | 14 (1.58) |
| 7-‐16 DIN | 222-‐267 (25.09-‐30.17) |
| 4.3-‐10 | 44 (5.00) |
Bend Radius
Avoid bending cables more than the minimum recommended bend radius.
Figure 4. Cable with a seven-centimeter bend radius
Twisting
Avoid twisting at ALL times.
Flexure
Flex cables as little as possible to ensure a long life.
Over-bending
Over-bending most often causes cable damage.
Flex Life
Cables are limited by the number of bend cycles. It is important to understand what defines a ‘cycle’. Check the manufacturer’s guidelines to determine the bend cycle measurements.
Testing
Electrostatic Discharge
Stay grounded and protect against electrostatic discharge (ESD) while connecting, testing, or cleaning cables or connectors. Wear a grounded wrist strap, a heel strap, and use a grounded conductive table mat on a conductive floor.
Electrical Inspection
Electrical tests are performed to determine measurement inaccuracies associated with unstable cables.
In-Process Stability Checks
This test is performed on the test cable in the “as calibrated” configuration. It should be performed immediately after calibration and periodically afterwards to verify stability and validate calibration.
Dynamic Stability “Thrum Test”
Hold cable lightly between your first and second finger while resting forearm on the test bench. Flex your wrist at approximately 2 beats per second (forearm remaining on the test bench).
Dynamic Stability “Stress Test”
This test shows evidence of cable or connector abuse. Hold cable lightly between your thumb and first finger of each hand around the area of concern. Flex the cable around, be careful not to exceed the minimum band radius. Repeat stress test for all areas of concern along with visual inspection of cable and connector junction.
360-Degree Wrap Test
For cables longer than 18 inches, perform this test. Save the S21 insertion loss and S21 phase data in memory and then display the math divide data. Disconnect test cable at port two end and wrap the cable 360 degrees at a 4.75-inch or manufacturer recommended diameter. Reconnect test cable at port two end. Cable should meet the manufacturer’s requirements. Disconnect test cable at port two end and return cable to its original configuration. Reconnect cable at the end of port two.
Four Quadrant Flex Test
For cable assemblies longer than 12 inches, perform this S11 Reflection test. Install a precision short on the port two end of the cable. Align the cable in a straight configuration perpendicular to the test equipment. Save the S11 phase data to memory and display math divide data. Flex the cable to 180 degrees at a 4.75 inch or at manufacturer’s required diameter. Verify that the cable meets manufacturer’s specifications. Repeat this test for each quadrant for a total of four quadrants, plus/minus 180 degrees in the XY and YZ planes.
Vector Network Analyzer Electrical Test
After performing visual and stability testing, a vector network analyzer may be used to test the cable’s insertion loss (attenuation) and the return loss (VSWR), by comparing the results obtained with the specifications in the cable’s datasheet. Follow manufacturer’s specifications for testing with a Vector Network Analyzer.
Figure 5. Keysight E5080A ENA Vector Network Analyzer RF Cable Test Setup
The Need For Calibration
Make sure the vector network analyzer has been properly calibrated prior to testing the cables and connectors.
Why do we have to calibrate?
- It is impossible to make perfect hardware
- It would be extremely difficult and expensive to make hardware good enough to entirely eliminate the need for error correction
How do we get accuracy?
- With vector-error-corrected calibration
- Not the same as the yearly instrument calibration
What does calibration do for us?
- Removes the largest contributor to measurement uncertainty: systematic errors
- Provides best picture of true performance of device under test
Advantages of Calibrating Your Precision Test and Measurement Instruments
- Provide repeatable accuracy, saving time, money, materials, and labor.
- Calibrating your precision test and measurement instruments is the easiest way to avoid errors.
- Reduce the risk of products failing in service.
- Save money from warranty and rework costs.
Cable and Connector Verification (Calibration and Testing Services)
To ensure that your cables and connectors are tested properly, we can help by providing verification services that include: visual inspection, stability tests, vector analyzer tests for insertion loss (attenuation) and the return loss (VSWR), and cable and connector calibration services.
Resources
Here are some checklists on care and maintenance of precision test equipment to help you with preventing unnecessary repairs.
Videos
Introducing Keysight E5080A ENA Vector Network Analyzer (YouTube video)
The best solution for PCB manufacturing test | E5063A PCB Analyzer | Keysight (YouTube video)
Tra-Cal Calibrates and Tests Cables and Connectors
Tra-Cal calibrates a broad range of test and measurement equipment, cables, and connectors:
- Cables and Connectors Verification (Calibration and Testing Services)
- Signal Analysis Equipment (vector network analyzers, spectrum analyzers, signal generators, and power meters
- Manual tools (calipers, dynamometric wrenches and screwdrivers, torque wrenches, etc.)
- Powered mechanical measurement tools (electric, pneumatics, hydraulic)
- Mechanical measurement meters
- Test benched (meters linked to a display)
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