Dealing with UK defence EMC standards
01 July 2020
In the military domain, EMC compliance is critical, since electromagnetic interference may severely impair radio communications & the functioning of other devices. Ministry of Defence (MoD) Def Stan 59-411 Issue 3 was issued on 14 June 2019 and provides the foundation for ensuring EMC in defence procurement.
This tutorial was originally featured in the July 2020 issue of EPDT magazine [read the digital issue]. Sign up to receive your own copy each month.
Here, Pete Dorey, Principal EMC Consultant at global product testing & certification organisation, TÜV SÜD talks us through some of the key elements to consider in this latest update…
TÜV SÜD has been working with aerospace & defence manufacturers for more than 50 years, and was an editor within the original MoD Def-Stan 59-411 EMC Working Group, carrying out development work in support of the Issue 3 update. As a leading radio & telecommunications certification body, TÜV SÜD BABT is also a Notified Body under the European Union’s Marine Equipment, Radio Equipment & Machinery Directives. Though Issue 3 covers a wide range of updates, many of which require too much detail for this article, I will highlight some key changes to consider herein.
Part 1: ‘Management & Planning’
Part 1 ‘Management and Planning’ addresses EMC throughout the project lifecycle, and assists project managers and contractors in selecting appropriate EMC activities, dependent on project size and complexity. It defines the documentation required, such as control plans, test plans and test reports.
Part 1 addresses this risk for COTS/MOTS procurement, and a risk assessment procedure is provided that requires electromagnetic (EM) environment definition, evaluation of EMC compliance evidence (for instance, by gap analysis), determination of functional criticality of the equipment and platform, and mitigation of unacceptable risks by remedial design, installation methods and retest. The MoD’s gap analysis evaluation tool has now been made available via the EMC Test Laboratory Association.
Part 1 Annex D has also been updated to include the latest guidance on compliance with the EU’s EMC Directive 2014/30/EU. As the application of EU directives to defence projects can lead to duplication of test programmes and additional costs, testing can be minimised by establishing technical documentation to demonstrate where Def Stan 59-411 satisfies EMC Directive requirements via gap analysis. This will ensure that the remaining unsatisfied requirements are tested using commercial standards. The manufacturer or supplier then makes a Declaration of Conformity and applies CE Marking, with the option of assistance from an EMC Notified Body.
Part 3: ‘Test Methods and Limits for Equipment & Sub Systems’
Part 3 ‘Test Methods and Limits for Equipment and Sub Systems’ has been updated with new antenna port tests and changes to the radiated emission tests.
Previously land service radiated emission tuned antenna test DRE03 required the use of obsolete “Clansman” radio equipment in the frequency range up to 30 MHz. Commercially available active rod antennas can now achieve the required sensitivity and DRE03 has been replaced with a “standard” radiated emission test DRE01. Test laboratories will need to ensure they have active rod antenna that meets the performance requirement. The DRE01 test set-up for rod antenna has been amended and the rod antenna counterpoise must now be isolated from the ground plane bench, whereas previously it was bonded.
However, there still remains the need to use the BOWMAN VHF Combat Net Radio antenna for test DRE03.A over the frequency range 30 MHz to 88 MHz, as this test is performed at 0.1 m separation and it is not possible to achieve sufficient sensitivity with an active rod antenna at 1 m separation.
Another main change to DRE01 is that the rod antenna test method used from 10 kHz to 30 MHz has been harmonised with NATO’s AECTP 501 standard (test NRE02 - Radiated Emissions, Electric Field, 10 kHz to 18 GHz) and the United States’ MIL-STD-461 (test RE102). This means that the rod antenna counterpoise must now be isolated from the ground plane bench, whereas previously it was bonded to the ground plane bench.
Antenna port tests were previously considered outside the scope of Def-Stan 59-411 and were not included in any other Defence Standards, but emissions can cause significant interference issues. The new antenna port emission tests therefore assess the contribution of unintentional emissions from antenna feeder cables and antennas when the radio is transmitting, on standby or receiving. The tests also apply to antenna power amplifiers. These new antenna ports tests have been added into Def Stan 59-411 Issue 3 by referencing the tests from NATO’s AECTP 500 series standard, thereby also achieving harmonisation.
The new antenna port susceptibility tests assess the radio receiver performance in the presence of other transmissions. This is of increasing importance due to the MoD spectrum release and sharing initiatives, where military and civilian users must co-exist compatibly in the same frequency bands. Due to the variety of radio technologies, the tests do not specify detailed methods and limits, but do provide guidance. Specialised test equipment is required for the antenna port susceptibility tests, including low noise signal generators, filters and couplers.
Part 4: ‘Platform and System Tests & Trials’
Part 4 ‘Platform and System Tests and Trials’ applies to whole platform and large system test and trials. Annex A provides Air Service procedures for whole aircraft EMC trials to assess aircraft compatibility with the external EM environment and with on-board EM sources.
Updates have been made to the Annex B Land Service radiated emission tests. This applies to Land Service military vehicle trials to ensure that communications performance is maintained when installed on the vehicle and while on the move, as well as ensuring that vehicle safety is not compromised by high-power radio transmissions. Radiated emission test DRE03 can be replaced with an equivalent test DRE01 using an active rod antenna over the frequency range 1.6 MHz to 30 MHz, as long as precautions are taken to avoid overload of the antenna.
A new test, DRE05 Electric Field radiated Emissions, provides an alternative method to DRE04 in the HF band 1.6 MHz to 30 MHz. This uses an active rod antenna installed in place of the vehicle antenna. No test limits are specified and the test result must be sent to the MoD ISS-Spectrum Electromagnetic Environmental Effects Authority (E3A) for assessment.
Part 5 provides design guidance with sections to cover air, land and sea applications, and addresses EMC fundamentals, equipment and platform design. There are no major changes to this part of the standard.
While I have provided a brief overview, it is clear that military EMC standards are significantly more onerous and time-consuming than commercial ones. This is due to the range of military radio and radar equipment that are required to operate on military platforms, resulting in a harsh electromagnetic (EM) environment. Since electromagnetic interference may severely impair radio communications and the functioning of other devices, EMC compliance is therefore critical.
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