Calibration and Application of Precision Test Cable Assemblies

2022-09-14 10:03:23 Jiaxing Focusimple Electronics Co., Ltd. Viewd 787

High precision test cable assembly is a widely utilized RF product, and is a commonly used high-precision system test consumable in the field of wireless communication. Test cable assemblies such as FABTest and VNA test series are usually connected with test instruments during application. Precision test cable assemblies are favored by the majority of instrumentation users for the measurement accuracy, consistency and stability. However, high-precision test cable assemblies are also faced with difficulties in operating and maintenance. In order to ensure the repeatability of measurement, prolong the service life, and improve measurement accuracy, users need to select appropriate installing and uninstalling tools when applying test cable assemblies. A clear Work Instruction will be needed even for skilled operators.


1. Appropriate handling tools

Appropriate torque on test cable assemblies not only improves the repeatability of measurements, but also extends the life of the test cable assemblies and measuring instruments. In mmWave applications, the tightening torque on the connector will have a significant impact on the measurement results. Consistent torque is required for repeatable measurements across all connections in the same instrument setup. An appropriate torque wrench prevents interface damage from over-tightening and helps the test cable reach its rated service life.

1. Make sure that the torque setting of the torque wrench is correct before use.

2. Place the torque wrench within 90° of the other wrench of the fixture or cable

3. Hold the torque wrench handle lightly and apply force perpendicular to the torque wrench handle. Tighten until the torque wrench "break point is reached, do not exceed the initial break point


Recommended mounting torques


Nut thread

Nut Size

Recommended   torques

SMA/3.5mm/2.92mm   male


8.0 HEX.

8 in-lbs (90   N-cm)

2.4mm/1.85mm male


8.0 HEX.

8 in-lbs (90   N-cm)

1.0mm male


6.0 HEX.

4 in-lbs (45   N-cm)

N male


19.0 HEX.

12 in-lbs (135   N-cm)

TNC male


14.0 HEX.

12 in-lbs (135   N-cm)

NMD 3.5mm/2.92mm   male


20.0 HEX.

15 in-lbs (170   N-cm)

NMD 2.4mm/1.85mm   male


20.0 HEX.

15 in-lbs (170   N-cm)

NMD 1.0mm


13.0 HEX.

12 in-lbs (135   N-cm)

If corresponding torque wrenches are needed, please contact Focusimple Electronics.


2. Calibration and Operation


●  Waiting for about an hour to warm up before calibration, if VNA is turned on for the first time;

  Remove the dust cap of the connector beforehand, otherwise the dust may get attached to the connector interface and may affect the test results;

  The connector interface of the calibration part should be placed downward to the table to prevent the calibration part from dust, impurities and debris;

  Do not utilize it directly before VNA is properly calibrated, as the accurate calibration result cannot be obtained;

  Calibrate the cable assembly before each application, as air temperature and humidity may affect the test results. Although the calibration information can be saved and recalled, it is not recommended for accuracy.  




1.  Wear a grounded wrist strap having a 1 MW series resistor. (A protection resistance of 10Ω);

2.  Inspect, clean, and gauge connectors. All connectors must be undamaged, clean, and within mechanical specification;

3.  Carefully align center axis of both devices. Push the connectors straight together so they can engage smoothly. The male center conductor pin must slip concentrically

into the contact finger of the female connector;



4. Rotate only the connector nut - NOT THE DEVICE OR CONNECTOR BODY – until finger-tight, being careful not to cross the threads. Damage to both connectors will occur if the male center pin is allowed to rotate in the female contact fingers;


5. Use a torque wrench to make final connection. Tighten until the "break" point of the torque wrench is reached. Do not push beyond initial break point. Use additional wrench, if needed, to prevent device body from turning.


3. Maintenance

●  The test cable assembly should not be placed/stored to be damp, heated, corroded or bumped;

  Replace the test cable assembly if has been used more than 5,000 times;

  Not to exceed the minimum bending radius of the cable (about 10 times the cable diameter) when the test cable assembly is bent.