Teseq Conducted RF Test System

What is Conducted RF?

Conducted RF is electromagnetic inference (EMI) generated by a transmitting device that exposes local equipment to varying RF levels through coupling onto different lines and cabling including power and data. Given the vast number of transmitting devices operating today this type testing is required from both a compliance and product reliability standpoint.

RF conducting along cables towards TV and light

Unlike radiated RF, conducted RF is focused on coupling and exposure via connected transmission. Both capacitive and inductive coupling methods have the potential to provide transmissions of noise onto associated cables providing a path towards the electronic or electrical devices.[1]

The varying levels of RF traveling down these conducted cabling paths will vary in strength in relation to the field that they are exposed to, among other factors. The greater the electric or magnetic (E and H) fields [2], measured in V/m, the higher the level of RF noise that can be expected traveling along the associated cabling. These levels will also vary dependent upon the environment and application of electrical equipment.

This brief post is only an introduction for purposes of familiarity with this type EMI event, for additional information please reference associated standards or links provided below.

Why it's tested

The goal of EMC and EMI testing is to ensure that devices function properly in their intended electromagnetic environments. To put it simply, to be sure that devices don't unexpectedly stop working (or cause another device nearby to stop working) given the environment which they operate.[3] All cables can carry RF voltage and currents, and given the vast amount of radiating devices, it is crucial from a compliance and product reliability perspective this testing is performed.

The end state is to ensure the design of devices is sufficient to handle the exposure to this type of EMI interference. The exact level, methods, and equipment needed will be determined by the underlying standard and method. The standard will also provide what it constitutes as passing or failing criteria allowing for products to be certified and degree of certainty it will function as intended.

Common Required Equipment

Basic Requirements

 Common components of Conducted RF Test System

The fundamental components that are required include a signal generator, amplifier, dual directional coupler, power meter, sensor, and any coupling specific or standard required equipment. These can either be external equipment that communicate using software, or components in a more complete box solution. Regardless of the setup using EMC/EMI software for these types of tests is highly recommended as it saves considerable time during the calibration process.

Signal Generator

The signal generator must be able to provide amplitude modulation AM (often 80%) with a 1 kHz sine wave. This is determined by the associated test standard and must cover the associated range which testing is conducted. The setup can include either an external stand alone generator, which is more typically at higher test levels (given the need for an external amplifier), or an internal one built into the test system.

Amplifiers

Conducted RF testing also requires equipment to boost or amplify the signal in an effort to meet testing requirements. The exact frequency and wattage required of the amplifier will be determined by the associated method and standard. The more power intensive methods and levels will typically require around ~100 watts (or higher) in order to create the required levels.

 Teseq CBA 400M-110 Amplifier

Two of the most common external amplifiers used for BCI testing (discussed in depth later) are the Teseq CBA 400M-110 and Amplifier Research 100A400AM20. These amplifiers will begin at the lower frequency levels of 4 kHz and typically go up to 400 MHz, covering a variety of requirements for both automotive and military applications. Other amplifiers can also be used so long as both the frequency range and power are sufficient to meet testing needs.

Test Systems

Coupling/Test Methods

Common Test Methods

The information below on the test methods will be based mainly around the most common commercial standard, IEC 61000-4-6, which has been harmonized with the European EN 61000-4-6[1]. There are many standards including military and automotive that may have slightly different methodologies, however they generally follow similar concepts with varying test levels. As we work our way through each of the most common methods, keep in mind that when conducting each, the underlying standard's methodology must be followed to ensure compliance.

IEC 61000-4-6:2013 places specific requirements on when each method should and should not be used. From a testing and compliance perspective CDNs are the preferred method and are the first choice in Figure 12 (injection method rules).

 Conducted RF Standards, Methods, Frequency and correpsonding equipment reference guide

Typically testing for conducted RF testing begins around 150 kHz to 230 MHz for commercial applications, and opens up for military and automotive requirements. MIL-STD-461 CS114 starts as low as 4 kHz ending at 200 MHz, whereas some automotive requirements have testing as high as 1 GHz. Some standards also specify modulation of RF signal at a certain percentage beyond which is required by IEC 61000-4-6. 

As we give a brief description of each method below, we will spend some time on the calibration setup. This step is crucial as it provides the necessary data for the test equipment and verifies appropriate test levels can be met. General settings are often saved by standards in the associated software or system, however the calibrations should be run every time the setup is changed. 

Conducted RF Equipment Rental Categories

Coupling Decoupling Network (CDNs)

CDNs are generally considered the preferred test method because they are able to ensure repeatable, accurate results and measurements. These networks are designed specifically for a particular port or cable type (power, communication, etc.). This has the potential to lead to multiple CDNs required for testing depending upon the test plan and ports tested. The most common CDN types include:

Conducted RF CDN Method common Types
  • CDN-S1 - Screened Cables
  • CDN-M1/-M2/-M3 - Unscreened Supply (Mains) Lines
  • CDN AF2 & AF8 - Unscreened Unbalanced Lines
  • CDN T2, T4, & T8 - Unscreened Balanced Pairs

The vast number of coupling decoupling networks available relate to the variety of different cables and ports tested. Teseq, a manufacturer of EMC equipment, provides an excellent guide that goes into great detail on the variety of CDNs available. The guide can be accessed by clicking here.

Typical CDN Method Calibration Setup

Common CDN Calibration setup
  • 1) Conducted RF Test System (NSG 4070)
  • 2) Adapter (100Ω)
  • 3) 6 dB Attenuator
  • 4) Coupling Decoupling Network (CDN)
  • 5) 50 Ω Termination Load

Direct Injection

This method requires a physical connection from the RF generator to the cabling of the device or equipment under test. This can involve some work as it is required to make manual connections including splitting the EUT cabling. This method when used for IEC 61000-4-6 also requires capacitors and resistors put in place between the connection.

Electromagnetic (EM) Clamp

 EM101 Clamp close up with split ferrite visible

EM Clamps as defined by IEC 61000-4-6 are typically used when CDNs aren't applicable as a more suitable option. The clamps themselves are made of ferrite as well as conductor and insulating plates providing a combination of inductive and capacitive coupling. The ferrite used in construction of the clamp must be in good condition, both on the top and bottom, for the equipment to be functional. Depending upon how testing is conducted other CDNs or EM Decouplers are often used to limit the RF after the DUT/EUT protecting auxilliary equipment.

It is important to consider the cable length available and thickness of the cables or bundles when using EM clamps. Most clamps have a length between 58 inchs and 70 inchs (not including decoupler or auxiliary equipment). The diameter of most clamps is fairly small, with most being around 20 mm, this small window limits the capabilities for larger bundles of cables or wires.

Typical EM Clamp Method Calibration Setup

Common EM Clamp test setup with EM101 and NSG 4070
  • 1) Conducted RF Test System (NSG 4070)
  • 2) CAL 801A 100Ω Adapters
  • 3) 6 dB Attenuator
  • 4) EM Test EM101 Clamp
  • 5) 50 Ω Termination Load
  • 6) Calibration Cable

Bulk Current Injection (BCI)

 Common Bulk Current Injection (BCI) probes including frequency range & power

The bulk current injection method is commonly required for many military and automotive applications and includes a similar methodology for injection as that of the EM Clamp. The component that induces the associated RF onto the cable(s) is the current injection probe (CIP). These probes use split ferrite pieces with a clamping mechanism as way of injecting required current levels onto cables and associated connected devices.

A major benefit of using this method is having a sizable window or opening on the injection probe, typically 43 mm and a clamping feature. This is ideal for situations where RF testing is required on bundles of cables, where otherwise testing would be substantially more difficult. This is also an easier solution when cabling cannot be cut, because the clamp can be opened and closed around the wires/cables.

This method is measured in either mA or dBµA with a current monitoring probe during calibration processes. Typical frequency ranges start at around 4 kHz to 400 MHz with some automotive requirements going into the Gigahertz range. This test typically requires the most power to drive enough RF though the injection probe, often requiring external power amplifiers mentioned above.  

Typical BCI Calibration Setup
 Typical Bulk Current Injection (BCI) Setup including labels
  • 1) 20dB attenuator 10 W (for >100 mA)
  • 2) 150Ω to 50Ω BCI Impedance Adapters
  • 3) Fischer FCC-BCICF-6-150 Cal Fixture
  • 4) Fischer F-120-9A Injection Probe
  • 5) 50 Ω Termination Load

Bulk Current Injection Setup Video

Common Questions

What test method do I use?

This isn't a question that has an easy answer. Choosing the correct method relates to the both the standard and equipment under test criteria. Some standards offer different methods, such as IEC 61000-4-6 providing CDNs, EM Clamps, and current injection, however others require only BCI with different ways it can be applied to the EUT/DUT.

References/Additional Information

[1]https://www.emcstandards.co.uk/files/61000-4-6_immunity_to_conducted_rfi_2_1.pdf

[2]https://atlasce.com/services/immunity-testing/conducted-rf-testing/

[3]https://www.fuseco.com.au/articles/what-is-rfi-emi-emc

http://www.unitest.com/pdf/RF_immunity_testing_e_3.pdf

https://www.rfvenue.com/blog/2014/12/14/common-sources-of-interference

https://www.teseq.com/applications/induced-rf-i.php

 

Conducted RF Systems

Teseq NSG 4070 Laptop - Front SideTeseq NSG 4070 - Front
NSG 4070 Rental - Teseq Conducted RF Test System
  • 80 Watt Radiated & Conducted RF System
  • Built-in Signal Generator, Amplifier, & Power Meter 
  • Easy to use with BCI, EM Clamp, or CDN Testing
CWS 500N 1.4 & Laptop - FrontEM Test CWS 500N - Back
CWS 500N1.4 Rental - EM Test RF Immunity Test System
  • EM Test 80 RF Test System Including Software
  • Ideal for IEC 61000-4-6 Conducted Immunity Tests
  • BCI, CDN, & EM Clamp Equipment Availible 
Amplifier Research CI00402 Rental - Conducted RF System
Amplifier Research CI00402 Rental - Conducted RF System
  • AR 100Watt Conducted RF System & Software
  • Meets MIL-STD-461 CS114 & ISO 11452-4 Levels
  • Rented for Higher Current BCI Testing