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ministration 

esearch Center

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entation of an 
Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 

Acknowledgments 

The author is grateful for the contributions to the work described here by the following 

individuals: Sandra V. Koppen, Mahyar M. Malekpour, Paul S. Miner, Celeste M. 

Belcastro, Eric G. Cooper, Jay J. Ely, Dr. Oscar R. Gonzalez, Dr. W. Steven Gray, John 

J. Mielnik, Jr., Truong X. Nguyen, Maria Theresa Salud, and Laura J. Smith. 
iii

Abstract 

An experiment was conducted to characterize the effects of 

HIRF-induced upsets on a prototype onboard data network. The 

experiment was conducted at the NASA Langley Research 

Center’s High Intensity Radiation Field Laboratory and used a 

generic distributed system prototyping platform to realize the 

data network. This report presents the results of the hardware 

susceptibility threshold characterization which examined the 

dependence of measured susceptibility on factors like the 

frequency and modulation of the radiation, layout of the physical 

nodes and position of the nodes in the test chamber. The report 

also includes lesssons learned during the development and 

execution of the experiment. 
iv

Table of Contents 

1. Introduction ................................................................................................................................................ 1

2. HSTC Background ..................................................................................................................................... 3

3. HSTC Description ...................................................................................................................................... 9

4. Results and Analysis................................................................................................................................. 15

4.1. Power Cable Routing......................................................................................................................... 15

4.2. Modulation ........................................................................................................................................ 16

4.3. Physical Nodes .................................................................................................................................. 18

4.4. Chamber Positions............................................................................................................................. 22

5. Final Remarks........................................................................................................................................... 24

Appendix A. Test Data................................................................................................................................. 26

References .................................................................................................................................................... 38

Acronyms ..................................................................................................................................................... 40
1

1. Introduction 

An experiment was conducted to characterize the effects of a HIRF (High Intensity Radiated 

electromagnetic Field) environment on a prototype of an onboard data network [1, 2, 3]. This network 

provides the capabilities needed to develop processing architectures satisfying a wide range of application 

performance and dependability requirements, including Integrated Modular Architectures (IMA) [4] for 

safety-critical real-time applications [5, 6, 7, 8]. A distributed system architecture for those applications 

must have the ability to mitigate the effects of internal component faults of varying severity [9]. The 

potential of HIRF environments to generate severe fault conditions in electronic systems [10, 11] was 

leveraged in this physical fault injection experiment [12, 13] to examine the network’s fault response. 

The experiment was divided in two parts. The HIRF Susceptibility Threshold Characterization (HSTC) 

was intended to examine factors that determine the minimum HIRF field strength level at which a 

particular electronic System Under Test (SUT) begins to experience HIRF-induced interference to its 

internal operation. The results and lessons learned in HSTC were used to finalize the specification of the 

second part of the experiment. The HIRF Effects Characterization (HEC) was intended to assess the 

system response to functional system upsets (i.e., functional error modes which involve no component 

damage and can occur simultaneously in all channels of a redundant system [14]) over a range of severity 

levels. This report documents the results of the HSTC part of the experiment. The results of the HEC

will appear in future reports. 

Figure 1: ROBUS-2 topology 

The data network used in this experiment was ROBUS-2 [15, 16]. Figure 1 shows the ROBUS-2 

topology. The network has a redundant active-star architecture with the Bus Interface Units (BIUs) 

serving as the access ports, and the Redundancy Management Units (RMUs) providing connectivity as 

network hubs. The network between BIUs and RMUs forms a complete bipartite graph in which each 

node is directly connected to every node of the opposite kind. All the communication links are 

bidirectional. At the interface to the PEs, ROBUS-2 behaves as a shared-medium communication bus 

with a TDMA (Time-Division Multiple Access) channel access pattern. ROBUS-2 was designed to be 

implemented as a set of custom hardware-level protocol processors performing ROBUS-2-specific 

functions hosted on a hardware platform providing basic communication resources at the physical layer. 

The design of the protocol processors is described in the VHDL language [17, 18] and can be realized 

either on an FPGA (Field-Programmable Gate Array chip) or an ASIC (Application-Specific Integrated 

Circuit). For this experiment, ROBUS-2 was implemented on the Reconfigurable SPIDER Prototyping 

Platform (RSPP), which is a general-purpose prototyping platform for distributed systems consisting of

1 2 M

PEs 

BIUs 

RMUs 

1 2 N

1 2 N

ROBUS 

ROBUS 

Interface 
2

FPGA-based nodes and fiber-optic communication links. Additional information about the physical 

prototyping platform is given in reports [1] and [2]. 

The experiment was conducted at the NASA Langley Research Center’s High Intensity Radiated 

Fields (HIRF) Laboratory using reverberation chamber A of the facility to generate the HIRF 

environment [1]. Similar to a large microwave oven, the reverberation chamber operates as a cavity 

resonator in which the electric field generated by a transmitting antenna reflects off the metal walls

forming complex three-dimensional electromagnetic field patterns with low energy loss. Rotating 

mechanical stirrers in the chamber effectively change the boundary conditions (i.e., spatial orientation of 

the reflective surfaces) in time, thus creating a time-varying field pattern that mixes the energy and

produces a statistically uniform and isotropic HIRF environment. Figure 2 shows the inside of the 

chamber with the positions where the prototyping platform nodes could be placed on either nonconductive foam blocks or tables. 

Figure 2: Reverberation chamber A with non-conductive foam blocks and tables 

The purpose of HEC part of the experiment was to collect data on the response of the ROBUS-2 

function to physical faults occurring on the prototyping platform caused by electromagnetic interference 

in the HIRF environment inside the reverberation chamber. Multiple configurations were tested to enable 

comparative analysis of HIRF responses [1]. To support the HEC, the HSTC part of the experiment was 

designed to examine how the field-strength susceptibility threshold of the prototyping nodes depends on 

the physical layout of the nodes, the frequency of the input signal driving the chamber’s transmitting

antenna, the input signal modulation, which specific physical node is being radiated, the particular 

ROBUS-2 function hosted by a node and the position of a node in the chamber. The data collected during 

HSTC was used to specify the physical layout of a node, to specify the HIRF strength, frequency and 

modulation test points, and to rank the physical nodes by their average susceptibility thresholds and the 

chamber positions by their average field strengths. These node and position rankings were then used to 

assign ROBUS-2 functions to nodes and nodes to chamber positions in HEC in order to reasonably match 
3

the susceptibility thresholds of the various test configurations and thus reduce any possible biases in the 

HEC comparative response analyses due to differences in susceptibility thresholds among the tested 

configurations. The HSTC data was also used to specify how to scan the field strength and frequency 

during HEC tests to efficiently find upset susceptibility regions and minimize the likelihood of damaging 

the physical nodes from excessive radiated field coupling. 

The report is organized as follows. The next section gives an overview and insight into how the 

specification of HSTC changed over time until it reached its final form presented in report [1] as we 

learned about the implications of the chamber radiation parameters and the node layout on the 

susceptibility threshold and response of the physical nodes. This is followed by a description of the

HSTC objectives we settled on and the methodology used to achieve these objectives. Then the HSTC 

results and analysis are presented. The report ends with a summary and concluding remarks on the HSTC

part of the experiment. The appendix shows the susceptibility threshold data collected in HSTC. 

2. HSTC Background 

The purpose of the HSTC was to determine how to generate HIRF-induced upsets in the nodes of the 

prototyping platform. This section describes how the HSTC evolved from its initial form developed 

based on vague notions of the HIRF chamber field dynamics and the interaction of the field with 

electronic devices, to its final form shaped by lessons learned through experimentation and careful 

analysis of observations. The knowledge and experience gained in the development of the HSTC strongly

influenced not only the design of the HEC, but also the experiment design for a later project on the effects 

of HIRF on a distributed flight control system [19, 20, 21]. 

Our initial attempts to design a procedure to characterize the susceptibility threshold of the platform 

nodes leveraged existing descriptions of a mode-stirring reverberation chamber in which the field is 

isotropic, randomly polarized and uniform throughout the chamber. Essentially, we thought of the HIRF

field in a mode-stirred reverberation chamber as being similar to random noise whose amplitude and 

central frequency could be easily controlled by changing the parameters of the input signal to the 

transmitting antenna. Additionally, based on the guidelines in the RTCA/DO-160D standard [22] and 

considering that the platform nodes were going to be tested with open enclosures (see Figure 3), it was 

thought that a field strength of no more 100 V/m and 25 geometrically spaced discrete frequencies over

the range from 100 MHz to 1000 MHz would produce an adequate number of upset regions. 

Initially we focused our effort in defining field amplitude modulation patterns with timing parameters

derived from the analysis of the design of ROBUS-2. ROBUS-2 uses a full-system re-initialization 

strategy that is dependent on the assumption that the duration of external disturbances experienced by the 

system will be within an assumed maximum bound and that enough time will elapse between 

disturbances to allow the system to return to normal operation. There is no such assumption for scenarios 

in which a subset of nodes is affected by an external disturbance but the system remains operational in a 

degraded state. Thus, the experiment was viewed as a series of random-fault injection tests with the 

radiated field as the means of injecting faults. Each test of a hardware configuration was to be composed 

of a set of field exposures called rounds. Figure 4 illustrates the composition of a round. Each round 

consisted of a series of periodic radiation bursts called strikes, each of which was followed by a noradiation idle interval called a lull in which the radiated device was allowed to recover and return to 

normal operation. In general, each strike was composed of one or more radiation pulses called strokes. 
4

Figure 3: Nodes in chamber A with the shielding enclosures open (optical fibers not shown) 

Figure 4: Radiation time pattern for a test round in the initial version of the experiment 

The strokes were generated with a 1 KHz pulse modulation with a 90% depth and a pulse width of 20 

μs (i.e., large enough to accommodate the chamber time constant which measures the rate at which the 

field amplitude increases in the chamber in response to a step increase in the input signal amplitude). A 

series of strike patterns were defined with variations in the duration of the strikes (which determines the 

number of strokes), the strike period, and the number of strikes in a round. To test the robustness of 

Round

Strike

Lull

Field Intensity 

EMin

ETest

Stroke Stroke 

Period 

Strike Period 
5

ROBUS-2, the duration of the strikes were chosen to be either smaller or larger than the disturbance 

duration bound assumed in the design of ROBUS-2 (i.e., 150 ms). The strike periods were chosen to be 

larger than the expected worst-case recovery delay of ROBUS-2 (i.e., 2.15 seconds for individual node 

recovery and 4.18 seconds for full-system recovery) to ensure that each upset event could be handled in 

the analysis as an independent trial in a fault injection experiment. The actual strike periods were selected 

not to have a common divisor (i.e., were prime) relative to the duration of a stirrer rotation (i.e., 5 

seconds) such that the stirrers would be at a different position for each strike. The durations of the rounds 

were chosen to have a large enough number of upsets for a meaningful statistical analysis of system fault 

response. Round durations of up to 205 seconds (i.e., 3.4 minutes) were tested. The stirrers were set to 

rotate at 5 seconds per revolution. The field strength and frequency test matrix was covered by first

setting the desired field amplitude and varying the frequency over the whole range, then stepping up the 

field strength by 22.5 V/m and repeating the frequency sweep. One round was completed at each field 

strength and frequency test point, and every frequency was tested at every field strength level. At the 

time, it was assumed that the upset susceptibility threshold at a particular frequency was triggered by the 

field strength exceeding the immunity level of the most susceptible node components and that increasing 

the field strength beyond this level would trigger the failure of additional components and generate more 

complex (and interesting) node failure modes. Initially it was also assumed that all the nodes would have 

approximately the same susceptibility threshold profile over the frequency range because they are all 

physical replicas. Unfortunately, no upsets were observed with this initial setup with one node in the 

chamber at a predetermined position (i.e., node 4 at position 4). 

Figure 5: Layout of a node with the shielding enclosure removed 

The failure of the first experimental setup led to a process of trial-and-error exploration to find a 

reliable way to produce upsets. The first change was to completely remove the enclosures from the nodes 

to allow the electromagnetic field to directly reach the electronic components. The basic layout of a node 

with this change is illustrated in Figure 5. This proved not to be enough to generate upsets even after 
6

testing at every frequency and increasing the maximum field strength to 120 V/m. So the decision was 

made to continue increasing the field strength in steps of 20 V/m in an attempt to “calibrate” the test 

parameters by identifying the field-strength upset level at each frequency. Because it was noticed that the 

measured susceptibility threshold at a particular frequency sometimes was different when retesting for it, 

it was decided that after an upset occurred at a particular field strength, the same frequency would be 

tested at a higher field strength to confirm that a repeatable condition had been reached. A frequency was 

removed from the test set only after confirmation of the upset threshold. Table 1 shows the results of this 

test for node 4 at position 4. This test was followed by another test at 618.97 MHz that consisted of

running 10 rounds at 0, 20 and 40 V/m above the calibrated susceptibility threshold in order to confirm 

that the measured result was repeatable and that the node would indeed fail every time it was exposed to a 

field strength higher than the measured threshold. A positive result in this test lead us to believe that we 

had found a reliable way to generate upsets. 

Using the field-strength susceptibility profile in Table 1, a series of single-radiated-node tests were 

conducted in which rounds were executed at 0, 40 and 80 V/m above the calibrated threshold for each test 

frequency with a known susceptibility threshold. Although we were able to complete many rounds using 

different strike patterns, the radiated nodes experienced a large number of permanent component failures 

at an increasing rate. The failed components included in-stack power supplies, fan boards, CPUs, and 

FPGA boards. Figure 6 shows a power supply board which failed at 40 V/m above the susceptibility 

threshold. Notice the charred area indicative of overheating near the center of the board. While 

executing these rounds, it was noticed on the display of the AC-to-DC power supply in the Control Room

(which powered the radiated node in the chamber) that the current supplied to the node was slowly 

increasing as the radiation exposure continued. This was interpreted as an indication that the in-stack 

power supply at the radiated node was experiencing a cumulative overstress failure mode. At that point, 

it was realized that, considering how quickly we were losing parts, we would not be able to complete a

meaningful experiment before running out of spares and, more importantly, that most of the observed 

upsets were probably due to power supply degradation rather than interference effects on the logic 

components of the nodes. 

Table 1: Susceptibility thresholds measured during upset-level calibration test with explicit strike pattern 

Field Frequency 

(MHz) 

Susceptibility Threshold 

(V/m) 

Field Frequency 

(MHz) 

Susceptibility Threshold 

(V/m) 

100 320 348.07 560 

110.07 340 383.12 200 

121.15 380 421.7 160 

133.35 300 464.16 540 

146.78 380 510.9 Larger than 800 

161.56 180 562.34 780 

177.83 360 618.97 620 

195.73 280 681.29 Larger than 800 

215.44 Larger than 800 749.89 Larger than 800 

237.14 Larger than 800 825.4 Larger than 800 

261.02 Larger than 800 908.52 500 

287.3 Larger than 800 1000 Larger than 800 

316.23 800 -- -- 
7

Figure 6: Power supply board that failed at 40 V/m above the susceptibility threshold 

This situation lead us to reduce the number of strikes per round by 80% without changing the strike 

duration in order to reduce the total radiation exposure. This was implemented by increasing the period 

between strikes to allow additional time for the node’s power supply to stabilize between radiation bursts. 

However, this change was ineffective in reducing the rate of power supply failures as they continued to 

happen unabated. 

The next change tried was to replace the in-stack power supply from a 50 W rating to a 75 W rating to 

test a hypothesis that a more powerful device would also be more robust relative to HIRF radiation. This 

was quickly proved false as two 75 W power supplies failed in quick succession. 

We also tried moving the node to a different position in the chamber, but this change was also shown 

ineffective as the health monitoring system [2] located in the Control Room recorded a massive series of 

errors from the radiated node. Although the node’s components had not failed permanently, the volume 

of errors was viewed as an indication that the node was overwhelmed by the strength of the radiation and 

that continued exposure would quickly lead to a permanent failure. At this point, the experiment was 

suspended indefinitely until a new approach could be developed to generate logic upsets without causing 

permanent damage to the prototyping platform. 

Various observations were taken into consideration in the redesign of the experiment. A critical 

observation was that the most susceptible node component was the in-stack power supply and that 

although its design enabled it to absorb radiation for a long time with minimal effect at its output, 

eventually the total radiation exposure would cause it to fail permanently. It was assumed that a high 

field strength would accelerate the failure of the power supply. 
8

Figure 7: Peak field amplitude during a strike measured at the output of the receive antenna in the chamber 

Figure 7 illustrates a casual observation that turned out to be one of the most significant insights into 

the operation of the reverberation chamber and eventually lead to the successful redesign of the 

experiment. This figure shows an oscilloscope trace of the peak field strength amplitude during a strike 

measured at the output of the receive antenna which is located inside the reverberation chamber. Notice 

how the amplitude varies in time and recall that the field stirrers in the chamber were constantly rotating 

during a round. In the particular round during which this measurement was made, the strikes had a 

duration of 100 ms and the stirrers had a revolution period of 5 seconds. Therefore, the shown peak fieldamplitude trace covers only a small fraction of a stirrer’s revolution. Contrary to what had been assumed, 

the peak field strength at a position in the chamber during a strike was not constant in time but a function 

of the angular position of the stirrers. From this it was deduced that this time varying stirrer-induced 

field-strength-amplitude modulation (SIM) was how the stirrers made the field uniform (in a statistical 

sampling sense) throughout the chamber. Therefore, in effect, our pulse-based strike pattern was 

sampling this SIM waveform, and based on the large SIM amplitude variation seen in Figure 7, the nodes

were being exposed to radiation bursts of widely varying and essentially random field strengths. This

would help explain, in part, why repeatability of test results was so poor and why we saw so many long

sequences of testing with no observed effects even after increasing the nominal severity of the HIRF 

environment. 

The HSTC approach described in the next section incorporated the lessons learned from this initial 

attempt to define a safe and reliable methodology to generate HIRF-induced upsets. 
9

3. HSTC Description 

The purpose of the HSTC was to characterize the dependence of the HIRF susceptibility threshold of 

the prototyping platform nodes to variations in the field frequency, modulation, physical layout of the 

nodes, individual nodes, and positions in the chamber. To account for possible irremediable differences 

in the susceptibility thresholds of the nodes or the relative strength of the field at the various test positions 

in the chamber, the data collected in the HSTC had to support an analysis to rank the nodes by their 

immunity to HIRF and the positions by the severity of their local environments. Table 2 on page 13 of

report [2] shows the planned test sequence for the HSTC. Table 3 below shows the actual tests 

performed. Figures 8 and 9 illustrate the test setups for HSTC configurations HC3 and HC4. These 4x4

ROBUS-2 configurations with a single node in the chamber were selected for the HSTC for several 

reasons: (1) the theory of design of ROBUS-2 guaranteed that the nodes outside the chamber were 

immune to errors generated by the radiated node and they would preserve coordinated, error-free and 

highly deterministic operation in the value and time domains regardless of any behavior exhibited by the 

radiated node; (2) by virtue of their immunity to error from the radiated node, the nodes outside the 

chamber provided a stable message traffic environment that enabled efficient error recovery by the 

radiated node; (3) the low data transfer rate allowed the nodes to operate with non-overlapping reception 

windows, which increased the input error detection coverage (see Section 5 of report [2]); and (4) because 

there was a single node in the chamber, it was known that any observed errors originated from faults 

occurring at the radiated node. These conditions greatly simplified the analysis of HSTC results. 

Basically, any error reported by any of the System Health Monitors at either the PE Emulator or the Bus 

Monitor (see reports [1] and [2]) signaled that the radiated node was being exposed to a field strength at 

or above its susceptibility threshold. 

The field stirrers were set to rotate at 10 seconds per revolution and each test round lasted for 30 

seconds (i.e. 3 stirrer revolutions) at a particular field strength and frequency point. The relatively slow 

stirrer speed was meant to slow down the rate of change of the SIM waveform and enable longer exposure

of the node to every part the SIM. The round duration was set large enough to allow the node to be 

exposed to a few passes of the SIM. 

A 2-out-of-3 rule was used to confirm an observed susceptibility threshold. This rule required that a

susceptibility threshold observed during a round at a particular field strength and frequency had to be 

confirmed by repeating the round a total of at most three times and observing the susceptibility in two of 

the rounds. Report [1] describes this rule and its implementation in detail. 
10

Table 3: Actual HSTC tests performed 

HSTC 

Test 

Id 

Hardware 

Configuration 

Variable of 

Interest 

Functional 

ROBUS 

Node 

Physical 

RSPP 

node 

Chamber 

Position Modulation

Field 

Strength 

(V/m) 

1 HC3 Physical 

Node RMU 1 5 5 CW 20 - 300 

2 HC4 Physical 

Node BIU 1 1 5 CW 20 - 300 

3 HC4 Physical 

Node BIU 1 2 5 CW 20 - 300 

4 HC4 Physical 

Node BIU 1 3 5 CW 20 - 300 

5 HC4 Physical 

Node BIU 1 4 5 CW 20 - 300 

6 HC3 Physical 

Node RMU 1 6 5 CW 20 to 300 

7 HC3 Physical 

Node RMU 1 7 5 CW 20 - 300 

8 HC3 Physical 

Node RMU 1 8 5 CW 20 - 300 

9 HC3 Modulation RMU 1 5 5 Pulse 20 - 500 

10 HC4 Position BIU 1 1 1 CW 20 - 300 

11 HC4 Position BIU 1 2 2 CW 20 - 300 

12 HC4 Position BIU 1 3 3 CW 20 - 300 

13 HC4 Position BIU 1 4 4 CW 20 - 300 

14 HC3 Position RMU 1 6 6 CW 20 - 300 

15 HC3 Position RMU 1 7 7 CW 20 - 300 

16 HC3 Position RMU 1 8 8 CW 20 - 300 

17 HC3 Modulation RMU 1 5 5 Square 

wave 

20 - 400 

18 HC3 Power Cable 

Routing 1 RMU1 8 5 CW 20 - 300 

19 HC3 Power Cable 

Routing 2 RMU1 8 5 CW 20 - 300 

20 HC3 Power Cable 

Routing 3 RMU1 8 5 CW 20 - 300 

21 HC3 Power Cable 

Routing 4 RMU1 8 5 CW 20 - 300 

22 HC3 Power Cable 

Routing 2 RMU1 7 5 CW 20 - 300 
11

Figure 8: Test setup for hardware configuration HC3 

Figure 9: Test setup for hardware configuration HC4

BIUs 

RMUs 

Bus 

Repository Monitor 

Test 

Controller 

PE 

Emulator 

Switch

RS-232 

RS-232 

Ethernet 

Ethernet 

1

Control Room Chamber A 

4 3 2 1

4 3 2

PE and NFA Links 

Monitoring Links 

BIUs 

RMUs 

Bus 

Repository Monitor 

Test 

Controller 

PE 

Emulator 

Switch

RS-232 

RS-232 

Ethernet 

Ethernet 

4 3 2 1

4 3 2 1

Control Room Chamber A 

NFA Links 

PE Links 
12

Tests 1, 9, and 17 were intended to allow a comparative analysis of the effects of the transmit 

antenna’s input signal modulation on the susceptibility threshold of a node. Notice that the maximum 

field strength was 300 V/m for CW (no modulation), 400 V/m for square wave modulation (1 kHz with 

50% duty cycle), and 500 V/m for pulse modulation (20 μs pulses at a rate of 1 kHz). This increase in 

maximum field strength was driven by the opposite trend of decreasing SIM waveform sampling 

coverage achieved by the specified modulation patterns. CW achieves 100% coverage of the SIM 

waveform, the square waveform modulation achieves at least 50% coverage, and the pulse modulation 

achieves at least 2% coverage. (The coverage is higher than the duty cycle if the stirrer revolution period 

is not a multiple of the modulation period.) Unless the round duration is made larger in order to increase 

the number of SIM samples per round, a decrease in SIM coverage implies an uncertainty increase in the

ability to measure the susceptibility threshold of a node. The increase in maximum field strength was

intended to accommodate a chance scenario in which the node is exposed to relatively low field strength 

radiation simply due to the reduced coverage from sampling the SIM waveform. 

The variable of interest for tests 1 to 8 was the replication of physical nodes. These tests were 

intended to examine possible differences in the susceptibility threshold of the nodes resulting from small 

differences in the way they were assembled and laid out in the chamber. The data from these tests was

used to rank the physical nodes by their susceptibility thresholds. 

Tests 1 and 10 to 16 examined the relative differences in the strength of the local field at each of the 

established node positions in the reverberation chamber. The intent was to assess the effectiveness of the 

stirrers in achieving a uniform field strength distribution throughout the chamber. 

Tests 18 to 22 were added to the HSTC plan to examine the impact of the power cable routing from 

the end-cap to the node’s in-stack power supply (see Figure 10). These tests were intended to determine 

the impact of the physical layout of a node on its susceptibility threshold. Figures 11 to 14 show the 

routings 1 to 4, respectively, used for these tests. Notice that tests 18 to 21 used the same node 8, while 

test 22 used node 7 as this test was intended as a check to see if the results for node 8 also applied to other 

nodes. 

Two changes were added to the test procedure in order to protect the nodes from additional damage to 

the in-stack power supplies. First, the current drawn by the radiated node from the AC-to-DC power 

supply in the Control Room was constantly monitored by the Test Controller, and a test would be stopped 

automatically if the current exceeded a predetermined threshold set based on earlier observations of instack power supply failures. The second change was to monitor the state snapshots sent out by the 

radiated node (see report [2]) for any indication that its internal voltage level monitor triggered a reset. 

The voltage monitor on the CPU board was a built-in function that ensured that the board was allowed to 

run only when the input voltage was above a preset level. A reset triggered by the voltage monitor during 

a radiation round was viewed as an indication that the in-stack power supply was being overwhelmed by 

the radiation and that continued exposure would lead to a permanent failure. A policy was implemented

on the monitoring system by which the second detected voltage-monitor triggered reset would stop the 

round. After an event of this kind, no additional testing would be performed at or above the current field 

strength level at the current frequency. 
13

 Figure 10: Physical layout of a node in the reverberation chamber 

Figure 11: Power cable routing 1 

Power cable 
14

Figure 12: Power cable routing 2 

Figure 13: Power cable routing 3 
15

Figure 14: Power cable routing 4 

4. Results and Analysis 

This section is divided in four parts covering the results of the power cable routing tests, the 

modulation tests, the physical node tests and the chamber position tests. 

4.1. Power Cable Routing 

Figure 15 shows the measured susceptibility threshold profile for HSTC tests 18 to 22 in which the 

variable of interest was the routing of the power cable. The figure shows that the susceptibility threshold 

was lowest below 200 MHz and between 316.23 MHz and 510.9 MHz. The frequencies below 200 MHz 

had the lowest susceptibility thresholds, and there is a trend by which the susceptibility threshold 

increases with the frequency. Also notice that the two extreme routings (i.e., 1 and 4) resulted in the least 

susceptible (i.e., highest threshold) layouts, with routing 4 being the least susceptible. Routings 2 and 3 

resulted in very similar susceptibility threshold profiles across the tested frequency range, and routing 3 

was the most susceptible. In addition notice that the susceptibility profiles for nodes 7 and 8 with routing 

2 differ by a small amount at most frequencies. 

Comparing these susceptibility profiles with the routings shown in Figures 11 to 14, it seems that the

susceptibility threshold is related to amount of overlap between the power cable and green side-board. 

This side-board carried low-voltage bit-serial data signals between the FPGA board and the fiber-optic

transceiver modules (see reports [1] and [2]). Therefore, it was conjectured that the susceptibility 

threshold was determined by a coupling of radiated energy from the power cable to the signal wires on 

this side-board. 
16

The other HSTC tests were conducted with power cable routings somewhere in between routings 2 

and 3. 

Figure 15: Measured susceptibility thresholds with variation in the node’s power cable routing 

4.2. Modulation 

Figure 16 shows the measured susceptibility threshold profiles for tests 1, 9 and 17 with variation in

the amplitude modulation applied to the input signal driving the transmit antenna. The empty markers 

indicate that susceptibility was not detected at the maximum field strength level. The results show that 

the node was most susceptible below 200 MHz for every modulation. The second most susceptible 

frequency interval is from 383.12 MHz to 510.9 MHz. 

Interestingly, the measured susceptibility profiles for all the modulations were very similar despite the 

fact that there are very large differences in duty cycles: 2% for pulse, 50% for square wave, and 100% for 

CW. A low duty cycle implies a low coverage of the SIM waveform (i.e., the node is exposed to only a 

small part of the SIM), which was thought to be a strong determining factor in the local field experienced 

by a radiated node and the measured susceptibility threshold. This result may seem to contradict 

observations made during the earlier versions of the HSTC in which pulse amplitude modulation like the

strike pattern shown in Figure 4 reduced the repeatability of the susceptibility threshold measurements. 

However, there is one important difference between the earlier strike patterns and the modulations used 

here in that, in effect, only stroke-level modulation was used in tests 1, 9 and 17, and there was no strikelevel modulation. Crucially, the stroke-level amplitude modulation was at a frequency of 1 KHz (i.e., 1 

ms period) versus the multi-second periods for the strike-level modulations. Thus, with no strike-level 

Susceptibility Threshold: Various Power Cable Routings 

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

Node 8, Routing 1

Node 8, Routing 2

Node 8, Routing 3

Node 8, Routing 4

Node 7, Routing 2

Hardware Configuration: HC3, Modulation: CW, Position 5

Maximum Field Strength: 300.0 V/m

No upsets
17

modulation, the stroke-level modulations were in effect sampling the SIM waveform at a high rate (i.e., 

10,000 samples per stirrer revolution). We believe that this allowed the field strength amplitude 

experienced by the node in each test to follow closely the profile of the SIM waveform. It seems that it is 

not only the total coverage that matters, but also how that coverage is distributed in time. Also, it is 

known that for some electronic systems, the dwell time is an important determinant of susceptibility [22]. 

Evidently, the shortest dwell time of 20 μs on-time with pulse modulation was larger than the minimum 

dwell time needed to trigger HIRF-induced effects in our prototyping platform nodes. Report [23] offers 

additional insight into the effect of signal modulation on the measured susceptibility threshold of a device. 

Figure 16: Measured susceptibility thresholds with variation in the chamber’s input modulation 

If the reasoning described above is correct, some of the differences in the measured susceptibility 

thresholds probably had little to do with the modulation pattern and may be due to other still unexplained 

phenomena. For example, there is a range of variation of 180 V/m in the susceptibility thresholds 

measured at 161.56 MHz and 140 V/m at 195.73 MHz. The sudden drop in the threshold at 908.52 MHz 

and 1000 MHz for pulse modulation is also interesting. These variations are probably not related to the 

power cable routing because the tests used the same node with the same layout at the same position in the 

chamber. We suspect that these differences were due to the SIM waveforms being different in profile and 

peak amplitude in each of the tests. This experiment used a calibrated field-strength technique by which 

the recorded field strength during a radiation test was determined from a pre-test calibration of the input 

power required to generate a desired field-strength level at the receive antenna some distance away from 

where the nodes were positioned (see Figure 2 and Section 4.3 of report [1]). Thus, if the SIM waveforms 

during calibration and test were different, the actual field strength during a test could be different from the 

Susceptibility Threshold: Node 5, Position 5, Modulations: CW, SW, Pulse

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

450.0

500.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

CW

Square Wave

Pulse

Hardware Configuration: HC3

Maximum Field Strength: 300.0 V/m CW, 400.0 V/m SW, 500.0 V/m Pulse
18

calibrated strength. Likewise, if different tests had different SIM waveforms, the measured susceptibility 

threshold could be different. 

The next step is to find a plausible explanation for variations in the SIM waveforms of different tests. 

For this, it helps to consider a radiated field inside a reverberation chamber and what happens when the 

field stirrers rotate. As described in report [1], a reverberation chamber is modeled as a large cavity 

resonator characterized by three-dimensional stationary wave patterns determined by the boundary 

conditions in the chamber (i.e., the relative position of the reflective surfaces inside chamber). The two 

mechanical field stirrers with reflective paddles (see Figures 2 and 3) change the boundary conditions and 

create different field structures as they rotate. The SIM waveform at a point in the chamber is the peak 

field-strength amplitude as the stirrers go around. Because of the complex field structure inside the

chamber, the SIM waveform will be different at different points in the chamber. Furthermore, different 

angular offsets of the stirrers (see Figure 17) correspond to different boundary conditions, which create 

different field structures, which in turn produce different SIM waveforms. During the tests, the stirrers 

rotated at the same rate and maintained a constant angular offset relative to each other. Other than that, 

none of the HSTC tests controlled or specified this variable, and the tests did not measure the relation 

between the SIM waveforms and the relative angular offset of the stirrers. A future report will examine 

the relation between the SIM waveform characteristics and the angular offset of the stirrers using data 

collected after the HSTC test was completed. 

Figure 17: Illustration of relative angular offset for a pair of field stirrers rotating at the same speed 

 

4.3. Physical Nodes 

Figure 18 shows the susceptibility threshold results for HSTC tests 1 to 8 for physical nodes 1 to 8. 

The figure shows that there were three frequency intervals with susceptibility at or below the 300 V/m

maximum nominal field strength with CW modulation. The interval from 100 MHz to 195.73 MHz had 

the lowest susceptibility thresholds and there is a common trend of minimum thresholds near 100 MHz 

and increasing with frequency. The variability of the susceptibility threshold in this interval seems to 

increase as the average susceptibility threshold increases. There is additional susceptibility in the interval 

from 316.23 MHz to 510.9 MHz, and at frequency 908.52 MHz, but there is no obvious pattern to the 

susceptibility at these frequencies. There was no measured susceptibility for 11 of 25 tested frequencies. 

Based on the results shown in Figure 16, we would expect the susceptibility thresholds for most of those 

11 frequencies to be at around 500 V/m or less. 

Relative Angular Offset 

Stirrer 1 Stirrer 2 
19

Figure 18: Measured susceptibility thresholds for all physical nodes using CW 

Figures 19 and 20 separate the measured susceptibility thresholds for nodes 5 to 8 and 1 to 4, 

respectively. Each of the nodes 5 to 8 was programmed as RMU1 while being tested in configuration 

HC3, and nodes 1 to 4 were programmed as BIU1 in configuration HC4. All the nodes were tested at 

position 5 in the chamber. The RMUs showed susceptibility in three separate test frequency intervals and 

there was no susceptibility at 12 of the 25 test frequencies. The BIUs showed susceptibility below 200 

MHz and at 383.12 and 510.9 MHz, and no susceptibility was observed at 15 test frequencies. The data 

does not offer any additional insight into differences between nodes programmed as RMUs or BIUs. 

Overall, the differences in measured susceptibility thresholds are probably due to slight differences in the 

routing of the power cables or the SIM waveforms generated by the chamber. Another possible cause for

the differences in measurements could be the power output from the amplifier driving the transmit 

antenna. A diagram of the chamber test setup is shown in Figure 7 of report [1]. The power amplifier is 

designed to maintain a constant input-output gain, but this is complicated by the time-varying 

electromagnetic characteristics of the chamber as the stirrers rotate [23]. No data was collected during 

this experiment to examine this possible source of error in measured susceptibility thresholds. 

Table 4 shows the analysis for ranking the physical nodes by their measured susceptibility threshold. 

At each frequency, the nodes were ranked by increasing susceptibility threshold by assigning order 

indices from 1 to 8. Nodes with the same susceptibility threshold were assigned the same ranking index. 

A no-upset result at a specific frequency was assigned a ranking of 8. The frequencies at which none of 

the nodes showed susceptibility were removed from consideration. Nodes 5 and 7 had the same mean 

ranking. The overall ranking of nodes was as follows, by node id: 1, 8, 4, 6, 2, (5, 7), 3. Nodes 1 to 4 as 

BIUs ranked as follows: 1, 4, 2, 3. For nodes 5 to 8 as RMUs, the ranking was: 8, 6, (5, 7). 

Susceptibility Threshold: All Nodes, Position 5, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

Node 5

Node 6

Node 7

Node 8

Node 1

Node 2

Node 3

Node 4

Hardware Configuration: HC3 for Nodes 5-8 and HC4 for Nodes 1-4, Modulation: CW

Maximum Field Strength: 300.0 V/m

No upsets
20

Figure 19: Measured susceptibility threshold for physical nodes 5 to 8 programmed as RMUs 

Figure 20: Measured susceptibility threshold for physical nodes 1 to 4 programmed as BIUs 

Susceptibility Threshold: Nodes 5-8, Position 5, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

Node 5

Node 6

Node 7

Node 8

Hardware Configuration: HC3, Modulation: CW

Maximum Field Strength: 300.0 V/m

No upsets

Susceptibility Threshold: Nodes 1-4, Position 5, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

Node 1

Node 2

Node 3

Node 4

Hardware Configuration: HC4, Modulation: CW

Maximum Field Strength: 300.0 V/m

No upsets
21

Table 4: Worksheet for ranking physical RSPP nodes by measured susceptibility threshold 

All nodes at position 5, Modulation: CW

Susceptibility Threshold Field Strength (V/m) Susceptibility Threshold Rank (Lowest = 1 to Highest = 8)

Frequency Node 1 Node 2 Node 3 Node 4 Node 5 Node 6 Node 7 Node 8 Node 1 Node 2 Node 3 Node 4 Node 5 N

100.000 40.0 40.0 40.0 40.0 60.0 40.0 60.0 40.0 1 1 1 1 7 110.069 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 1 1 1 1 1 121.153 60.0 100.0 100.0 80.0 80.0 100.0 100.0 40.0 2 5 5 3 3 133.352 80.0 80.0 60.0 80.0 100.0 60.0 120.0 40.0 4 4 2 4 7 146.780 60.0 60.0 100.0 80.0 120.0 100.0 120.0 60.0 1 1 5 4 7 161.560 100.0 180.0 180.0 140.0 100.0 240.0 120.0 100.0 1 6 7 5 1 177.828 140.0 180.0 240.0 220.0 280.0 No upset No upset 180.0 1 2 5 4 6 195.734 180.0 240.0 240.0 220.0 No upset 180.0 No upset 260.0 1 4 4 3 8 215.443 No upset No upset No upset No upset No upset No upset No upset No upset237.137 No upset No upset No upset No upset No upset No upset No upset No upset261.016 No upset No upset No upset No upset No upset No upset No upset No upset287.298 No upset No upset No upset No upset No upset No upset No upset No upset316.228 No upset No upset No upset No upset No upset 180.0 300.0 No upset 8 8 8 8 8 348.070 No upset No upset No upset No upset No upset No upset No upset No upset383.119 220.0 No upset No upset No upset 260.0 280.0 260.0 No upset 1 8 8 8 2 421.697 No upset No upset No upset No upset No upset No upset No upset 280.0 8 8 8 8 8 464.159 No upset No upset No upset No upset No upset No upset No upset No upset510.897 300.0 No upset No upset 180.0 280.0 No upset No upset 260.0 4 8 8 1 3 562.341 300.0 No upset No upset 300.0 No upset No upset No upset No upset 1 8 8 1 8 618.966 No upset No upset No upset No upset No upset No upset No upset No upset681.292 No upset No upset No upset No upset No upset No upset No upset No upset749.894 No upset No upset No upset No upset No upset No upset No upset No upset825.404 No upset No upset No upset No upset No upset No upset No upset No upset908.518 No upset No upset No upset No upset No upset 280.0 220.0 240.0 8 8 8 8 8 

1000.000 No upset No upset No upset No upset No upset No upset No upset No upset

Count of 1 8 3 2 4 2 Count of 2 1 1 1 0 1 Count of 3 0 0 0 2 2 Count of 4 2 2 1 3 0 Count of 5 0 1 3 1 0 Count of 6 0 1 0 0 1 Count of 7 0 0 1 0 3 Count of 8 3 6 6 4 5 Total Number of Rankings 14 14 14 14 14 Sum (Rank*Count) 42 72 78 59 77 

Mean Rank 3.00 5.14 5.57 4.21 5.50 Overall Relative Susceptibility 1 5 8 3 6 BIU Relative Susceptibility 1 3 4 2 ** *RMU Relative Susceptibility **   **  3 
22

4.4. Chamber Positions 

Figure 21 shows the measured susceptibility thresholds for nodes 1 to 8 at their default positions in the 

chamber by which the position id is the same as the node id. As in Figure 18 for position 5, susceptibility 

was detected in three frequency intervals: below 200 MHz, from 316.23 MHz to 510.9 MHz, and at 

frequency 908.52 MHz. The basic trends for the full set of positions remain the same compared to the 

trends at position 5 only. The most remarkable feature in Figure 21 compared to Figure 18 is the large 

variability in measured susceptibility thresholds between 146.78 MHz and 195.73 MHz. There is also a 

significant drop in the average susceptibility threshold at 195.73 MHz. Obviously, this simply means that 

average field strength at positions other than 5 was lower than at position 5 for frequencies around 146.78 

MHz, and that the opposite was true near 195.73 MHz. (Recall that the reported field strength for a test 

round was the calibrated value, which represented an expected average throughout the chamber. The 

field was not measured and reported for each position individually.) However, we do not have insight 

about why this was so. We speculate that this may be due to inherent differences in the SIM patterns at 

the various positions and the limitations of the stirrers in achieving field uniformity throughout the

chamber. 

Figure 21: Measured susceptibility threshold for physical nodes 1 to 8 at their corresponding default positions 

Susceptibility Threshold: All Nodes, Default Position Assignment, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

Node 5, Position 5

Node 6, Position 6

Node 7, Position 7

Node 8, Position 8

Node 1, Position 1

Node 2, Position 2

Node 3, Position 3

Node 4, Position 4

Hardware Configuration: HC3 for Nodes 5-8 and HC4 for Nodes 1-4, Modulation: CW

Maximum Field Strength: 300.0 V/m

No upsets
23

Table 5: Worksheet for ranking chamber positions by measured node susceptibility thresholds 

Field Scaling Ratio (wrt Position 5) Field Strength Ranking (Lowest = 1 to Highest = 8)

Frequency Position 1 Position 2 Position 3 Position 4 Position 5 Position 6 Position 7 Position 8 Position 1 Position 2 Position 3 Position 4 Position 5 P

100.000 1.000 1.000 1.000 2.000 1.000 1.000 1.500 1.000 1 1 1 8 1 110.069 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1 1 1 1 1 121.153 1.500 1.667 1.000 1.000 1.000 1.667 1.667 0.500 5 6 2 2 2 133.352 1.333 1.333 1.000 1.333 1.000 0.750 1.200 0.500 6 6 3 6 3 146.780 0.600 0.333 0.556 0.667 1.000 1.250 1.500 1.000 3 1 2 4 5 161.560 0.556 1.000 < 0.6 0.467 1.000 1.200 1.000 0.714 2 5 3 1 5 177.828 0.778 0.750 < 0.8 0.846 1.000 ≈ 1.0 ≈ 1.0 0.750 3 1 4 5 6 

195.734 1.125 1.000 2.000 1.100 ≈ 1.0 0.900 > 1.0 1.182 6 2 8 5 3 

215.443237.137261.016287.298316.228 ≈ 1.0 ≈ 1.0 ≈ 1.0 ≈ 1.0 ≈ 1.0 0.900 < 1.0 ≈ 1.0 3 3 3 3 3 

348.070383.119 1.000 > 1.0 ≈ 1.0 > 1.15 1.000 1.273 1.182 ≈ 1.0 1 5 3 6 1 

421.697 ≈ 1.0 ≈ 1.0 ≈ 1.0 > 1.0 ≈ 1.0 ≈ 1.0 ≈ 1.0 < 0.93 2 2 2 8 2 

464.159510.897 < 1.0 ≈ 1.0 > 1.0 0.600 1.000 ≈ 1.0 > 1.0 1.000 2 5 7 1 3 

562.341 < 1.0 ≈ 1.0 ≈ 1.0 < 1.0 ≈ 1.0 ≈ 1.0 ≈ 1.0 ≈ 1.0 1 3 3 1 3 

618.966681.292749.894825.404908.518 ≈ 1.0 ≈ 1.0 > 1.0 ≈ 1.0 ≈ 1.0 1.077 1.000 0.800 4 4 8 4 4 

1000.000

Count of 1 4 4 2 4 3 Count of 2 3 2 3 1 2 Count of 3 3 2 5 1 5 Count of 4 1 1 1 2 1 Count of 5 1 3 0 2 2 Count of 6 2 2 0 2 1 Count of 7 0 0 1 0 0 Count of 8 0 0 2 2 0 Total Number of Rankings 14 14 14 14 14 Sum (Rank*Count) 40 45 50 55 42 Mean Rank 2.86 3.21 3.57 3.93 3.00 Overall Field Strength Ranking 2 4 5 6 3 Ranking for Positions 1-4 1 2 3 4 ** *Ranking for Positions 5-8 **   **  2 
24

Table 5 shows the analysis performed to rank the chamber positions by the relative average of their 

local field strength as inferred from the measured susceptibility thresholds. The empty rows are for 

frequencies for which no node at any position or field strength experienced an upset. These frequencies 

were removed from consideration in the ranking analysis of the positions. Section 5.5 in report [1] 

describes the model and reasoning supporting this analysis. It is assumed that the susceptibility threshold 

with respect to the actual local field strength experienced by a node is an inherent property of the node in 

the sense that whether the node is susceptible or not is determined by the strength of the field relative to 

the threshold of the node. Therefore, ignoring errors due to the measurement being carried out in a modestirred reverberation chamber, the difference in susceptibility thresholds measured at two different 

positions in the chamber is directly related to the relative strength of the field at these positions. A lower 

field strength will result in a higher measured susceptibility threshold, and vice versa. The ratio of the 

susceptibility thresholds is inversely proportional to the ratio of the field strengths. The field scaling ratio 

on the top left part of Table 5 measures the strength of the field at position x relative to position 5, which 

is the reference position. To handle cases in which no susceptibility was detected at a particular test 

frequency, it is assumed that the threshold was 300 V/m to compute the ratio, which is then 

complemented with a smaller than (<), larger than (>), or approximately equal (≈) sign depending on 

whether the denominator, numerator, or both are assumed to be 300 V/m. These signs are used in ranking 

the field ratios at each particular frequency, as shown on the top right side of Table 5. The average

ranking results are shown on the bottom right part of Table 5. The overall ranking was as follows, with 

positions 4 and 6 tied in sixth place: 8, 1, 5, 2, 3, (4, 6), 7. For position 1 to 4 which are used for nodes 1 

to 4, the computed average ranking was: 1, 2, 3, 4. For positions 5 to 8 used for nodes 5 to 8, the ranking 

was: 8, 5, 6, 7. 

An interesting observation is that the mean of the field strength ratios in Table 5 is 1.014, with a 

maximum of 2.000 and a minimum of 0.333. This gives a better sense of the performance of the modestirred reverberation chamber relative to the uniformity of the peak field strength and the error range in 

measurements of susceptibility thresholds. 

It is known that the large measurement errors in the mode-stirred reverberation chamber make 

unreliable the computed rankings of nodes and positions and that using them to match the susceptibility 

thresholds of the configurations in the HEC part of the experiment may not produce the desired effect of 

reducing possible biases in the HEC data due differences in susceptibility thresholds. Still, this approach 

was used because it is a simple methodical way of assigning ROBUS-2 functions to physical nodes and 

physical nodes to chamber positions. The configurations and results of the HEC experiment will be 

presented in a future report. 

5. Final Remarks 

An important motivation for the HSTC experiment was to have an opportunity to familiarize ourselves 

with the intricacies of using a reverberation chamber to generate functional system upsets suitable for the 

study of fault response in safety-critical systems. In the HSTC experiment, we examined how the layout 

of a physical node determines its susceptibility to HIRF and how the susceptibility profile of a node 

changes with the radiation frequency and modulation. We also examined differences in the susceptibility 

threshold profiles of a set of physical nodes due to slight differences in the way the nodes are assembled 

and laid out in the chamber. Additionally, we investigated differences in the local HIRF environment at 

various locations in the chamber. The HSTC experience enabled us to uncover the field amplitude 

modulation mechanism by which the mode stirrers homogenize the HIRF environment. This experience 
25

has given us a better understanding of the operation of the reverberation chamber and allowed us to 

develop a safe and reliable test methodology that has already proven its value in a collaborative research 

effort [19, 20, 21]. 

The results of the HSTC were used in the planning of the HEC experiment. The results of the HEC 

will be presented in a series of future reports. We will also report on analysis carried out to characterize 

the SIM phenomenon with respect to various parameters, including the angular offset of the mode stirrers. 

The Appendix presents the susceptibility threshold data collected during the HSTC experiment. 
26

Appendix A. Test Data 

Figures A.1 to A.22 show the susceptibility threshold measurements for the HSTC tests. Empty 

markers in the figures indicate that the susceptibility threshold was larger than the maximum field 

strength of 300 V/m. 

Figure A.1: Measured susceptibility profile for HSTC Test 1 

Susceptibility Threshold: Node 5, Position 5, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 1, Hardware Configuration: HC3, Modulation: CW

Maximum Field Strength: 300.0 V/m
27

Figure A.2: Measured susceptibility profile for HSTC Test 2 

Figure A.3: Measured susceptibility profile for HSTC Test 3 

Susceptibility Threshold: Node 1, Position 5, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 2, Hardware Configuration: HC4, Modulation: CW

Maximum Field Strength: 300.0 V/m

Susceptibility Threshold: Node 2, Position 5, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 3, Hardware Configuration: HC4, Modulation: CW

Maximum Field Strength: 300.0 V/m
28

Figure A.4: Measured susceptibility profile for HSTC Test 4 

Figure A.5: Measured susceptibility profile for HSTC Test 5 

Susceptibility Threshold: Node 3, Position 5, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 4, Hardware Configuration: HC4, Modulation: CW

Maximum Field Strength: 300.0 V/m

Susceptibility Threshold: Node 4, Position 5, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 5, Hardware Configuration: HC4, Modulation: CW

Maximum Field Strength: 300.0 V/m
29

Figure A.6: Measured susceptibility profile for HSTC Test 6 

Figure A.7: Measured susceptibility profile for HSTC Test 7 

Susceptibility Threshold: Node 6, Position 5, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 6, Hardware Configuration: HC3, Modulation: CW

Maximum Field Strength: 300.0 V/m

Susceptibility Threshold: Node 7, Position 5, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 7, Hardware Configuration: HC3, Modulation: CW

Maximum Field Strength: 300.0 V/m
30

Figure A.8: Measured susceptibility profile for HSTC Test 8 

Figure A.9: Measured susceptibility profile for HSTC Test 9 

Susceptibility Threshold: Node 8, Position 5, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 8, Hardware Configuration: HC3, Modulation: CW

Maximum Field Strength: 300.0 V/m

Susceptibility Threshold: Node 5, Position 5, Pulse AM

0.0

100.0

200.0

300.0

400.0

500.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 9, Hardware Configuration: HC3, Modulation: Pulse

Maximum Field Strength: 500.0 V/m
31

Figure A.10: Measured susceptibility profile for HSTC Test 10 

Figure A.11 Measured susceptibility profile for HSTC Test 11 

Susceptibility Threshold: Node 1, Position 1, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 10, Hardware Configuration: HC4, Modulation: CW

Maximum Field Strength: 300.0 V/m

Susceptibility Threshold: Node 2, Position 2, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 11, Hardware Configuration: HC4, Modulation: CW

Maximum Field Strength: 300.0 V/m
32

Figure A.12: Measured susceptibility profile for HSTC Test 12 

Figure A.13: Measured susceptibility profile for HSTC Test 13 

Susceptibility Threshold: Node 3, Position 3, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 12, Hardware Configuration: HC4, Modulation: CW

Maximum Field Strength: 300.0 V/m

Susceptibility Threshold: Node 4, Position 4, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 13, Hardware Configuration: HC4, Modulation: CW

Maximum Field Strength: 300.0 V/m
33

Figure A.14: Measured susceptibility profile for HSTC Test 14 

Figure A.15: Measured susceptibility profile for HSTC Test 15 

Susceptibility Threshold: Node 6, Position 6, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 14, Hardware Configuration: HC3, Modulation: CW

Maximum Field Strength: 300.0 V/m

Susceptibility Threshold: Node 7, Position 7, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 15, Hardware Configuration: HC3, Modulation: CW

Maximum Field Strength: 300.0 V/m
34

Figure A.16: Measured susceptibility profile for HSTC Test 16 

Figure A.17: Measured susceptibility profile for HSTC Test 17 

Susceptibility Threshold: Node 8, Position 8, CW

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

HSTC Test: 16, Hardware Configuration: HC3, Modulation: CW

Maximum Field Strength: 300.0 V/m

Susceptibility Threshold: Node 5, Position 5, SW AM

HSTC Test: 17, Hardware Configuration: HC3, Modulation: Square Wave

Maximum Field Strength: 400.0 V/m

0.0

100.0

200.0

300.0

400.0

500.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)
35

Figure A.18: Measured susceptibility profile for HSTC Test 18 

Figure A.19: Measured susceptibility profile for HSTC Test 19 

Susceptibility Threshold: Node 8, Position 5, CW

HSTC Test: 18, Hardware Configuration: HC3, Modulation: CW

Power Cable Rounting: 1, Maximum Field Strength: 300.0 V/m

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

Susceptibility Threshold: Node 8, Position 5, CW

HSTC Test: 19, Hardware Configuration: HC3, Modulation: CW

Power Cable Rounting: 2 , Maximum Field Strength: 300.0 V/m

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)
36

Figure A.20: Measured susceptibility profile for HSTC Test 20 

Figure A.21: Measured susceptibility profile for HSTC Test 21 

Susceptibility Threshold: Node 8, Position 5, CW

HSTC Test: 20, Hardware Configuration: HC3, Modulation: CW

Power Cable Rounting: 3 , Maximum Field Strength: 300.0 V/m

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)

Susceptibility Threshold: Node 8, Position 5, CW

HSTC Test: 21, Hardware Configuration: HC3, Modulation: CW

Power Cable Rounting: 4 , Maximum Field Strength: 300.0 V/m

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)
37

Figure A.22: Measured susceptibility profile for HSTC Test 22 

Susceptibility Threshold: Node 7, Position 5, CW

HSTC Test: 22, Hardware Configuration: HC3, Modulation: CW

Power Cable Rounting: 2 , Maximum Field Strength: 300.0 V/m

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

100.000110.069121.153133.352146.780161.560177.828195.734215.443237.137261.016287.298316.228348.070383.119421.697464.159510.897562.341618.966681.292749.894825.404908.518

1000.000

Frequency (MHz)

Field Strength (V/m)
38

References

[1] Torres-Pomales, W.; et al: Plan for the Characterization of HIRF Effects on a Fault-Tolerant Computer 

Communication System. NASA-TM-2008-215306, May 2008. 

[2] Torres-Pomales, W.; et al: Design of Test Articles and Monitoring System for the Characterization of 

HIRF Effects on a Fault-Tolerant Computer Communication Systems. NASA-TM-2008-215322, July 

2008. 

[3] http://shemesh.larc.nasa.gov/fm/spider/ 

[4] Ramaker, R.; Krug, W.; and Phebus, W.; Application of a Civil Integrated Modular Architecture to 

Military Transport Aircraft. 26th Digital Avionics Systems Conference (DASC ’07), October 21-25, 

2007, pp. 2.A.4-1 - 2.A.4.10. 

[5] Yeh, Y. C.: Design considerations in Boeing 777 fly-by-wire computers. The 3rd IEEE International 

Symposium on High-Assurance Systems Engineering (HASE ‘98), 1998, p. 64. 

[6] Yeh, Y. C.: Safety Critical Avionics for the 777 Primary Flight Controls System. 20th Digital Avionics 

Systems Conference (DASC ‘01), October 14 – 18, 2001, pp. 1C2/1 - 1C2/11 vol.1. 

[7] Yeh, Y. C.: Triple-Triple Redundant 777 Primary Flight Computer. 1996 IEEE Aerospace 

Applications Conference, volume 1, 1996, pp. 293 - 307. 

[8] Kopetz, Hermann. Real-Time Systems: Design Principles for Distributed Embedded Applications. 2nd

Edition, Springer, 2011. 

[9] Driscoll, Kevin, et al.: Data Network Criteria Evaluation Report. Federal Aviation Administration, 

DOT/FAA/AR-09/27, July 2009. 

[10] Fuller, Gerald L.: Understanding HIRF – High Intensity Radiated Fields. Aviation Communications, 

Inc., Leesburg, VA, 1995, p. 7-2. 

[11] Hess, Richard: Computing Platform Architectures for Robust Operation in the Presence of Lightning 

and Other Electromagnetic Threats. 16th Digital Avionics Systems Conference (DASC), 1997. 

[12] Arlat, Jean; et al: Comparison of Physical and Software-implemented Fault Injection Techniques. 

IEEE Transaction on Computers, Vol. 52, No. 9, September 2003, pp- 1115 - 1133. 

[13] Karlsson, J.; et al: Application of Three Physical Fault Injection Techniques to the Experimental 

Assessment of the MARS Architecture. Proc. 5th IFIP Working Conference on Dependable Computing 

for Critical Applications (DCCA-5), IEEE Computer Society Press, Urbana-Champaign, IL, USA, 

September 1995, pp. 267 - 287. 

[14] Belcastro, Celeste M.: Laboratory Test Methodology for Evaluating the Effects of Electromagnetic 

Disturbances on Fault-Tolerant Control Systems. NASA Technical Memorandum 101665, November 

1989. 

[15] Torres-Pomales, Wilfredo; et al: ROBUS-2: A Fault-Tolerant Broadcast Communication System. 

NASA/TM-2005-213540, March 2005. 
39

[16] Torres-Pomales, Wilfredo; et al: Design of the Protocol Processor for the ROBUS-2 Communication 

System. NASA/TM-2005-213934, November 2005. 

[17] Perry, Douglas: VHDL. Third Edition, McGraw-Hill, 1998. 

[18] http://opensource.arc.nasa.gov/project/robus-2/ 

[19] Wang, Rui; Gray, W. Steve; and González, Oscar R.: Experimental Validation of a Performance Model 

for a Distributed Recoverable Boeing 747 Flight Control System Subject to Digital Upsets. 

Proceedings of the 43rd IEEE Southeastern Symposium on System Theory, Auburn, Alabama, 2011, pp. 

13 - 19. 

[20] Yates, A.M.; et al: Design of a High-Intensity Radiated Field Fault Injection Experiment for a FaultTolerant Distributed Computation and Communication System. Proceedings of the 2010 Digital 

Avionics Systems Conference, Salt Lake City, Utah, 2010, pp. 4.E.3-1 - 15. 

[21] Torres-Pomales, Wilfredo; Yates, Amy M.; and Malekpour, Mahyar R.: Fault Injection and Monitoring 

Capability for a Fault-Tolerant Distributed Computation Sytem. NASA/TM-2010-216834, August 

2010. 

[22] RTCA DO-160D, Change No. 1, Environmental Conditions and Test Procedures for Airborne 

Equipment, Section 20, Radio Frequency Susceptibility (Radiated and Conducted), December 2000. 

[23] Ely, Jay J.; Nguyen, Truong X.; and Scearce, Stephen A.: The Influence of Modulated Signal Risetime 

in Flight Electronics Radiated Immunity Testing with Mode-Stirred Chamber. NASA/TM-2000-

209844, January 2000. 

 

 

 
40

Acronyms 

AC Alternating Current 

ASIC Application Specific Integrated Circuit 

ASCII American Standard Code for Information Interchange 

BIU Bus Interface Unit 

CCP Controller Coordination Protocol 

COTS Commercial Off-The-Shelf 

CPU Central Processing Unit 

CW Continuous Wave 

DC Direct Current 

DSI Derivation Systems, Inc. 

EM Electromagnetic 

EMI Electromagnetic Interference 

FHSTC Fine HIRF Susceptibility Threshold Characterization 

FPGA Field Programmable Gate Array 

FSM Finite State Machine 

HC Hardware Configuration 

HEC HIRF Effects Characterization 

HFA Hub Fault Analyzer 

HIRF High Intensity Radiated Field 

HSTC HIRF Susceptibility Threshold Characterization

IVHM Integrated Vehicle Health Management 

LUF Lowest Usable Frequency 

Mbps Mega-bits per second 

NFA Node Fault Analyzer 

NIST National Institute of Standards and Technology

PE Processing Element 

RC Reverberation Chamber 

RF Radio Frequency 

RMU Redundancy Management Unit 

ROBUS Robust Bus 

RPP ROBUS Protocol Processor 

RSPP Reconfigurable SPIDER Prototyping Platform 

RTCA Radio Technical Commission for Aeronautics 

SBIR Small Business Innovation Research 

SHM System Health Monitor 

SIM Stirrer Induced Modulation 

SPIDER Scalable Processor-Independent Design for Extended Reliability 

SUT System Under Test 

TCS Test Control System 

TDMA Time Division Multiple Access 

VHDL VHSIC Hardware Description Language 

VHSIC Very High Speed Integrated Circuit 

 
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2. REPORT TYPE 

Technical Memorandum

 4. TITLE AND SUBTITLE

Characterization of HIRF Susceptibility Threshold for a Prototype 

Implementation of an Onboard Data Network 

5a. CONTRACT NUMBER

 6. AUTHOR(S)

Torres-Pomales, Wilfredo

 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Langley Research Center

Hampton, VA 23681-2199

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National Aeronautics and Space Administration

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NASA

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14. ABSTRACT

An experiment was conducted to characterize the effects of HIRF-induced upsets on a prototype onboard data network. The 

experiment was conducted at the NASA Langley Research Center’s High Intensity Radiation Field Laboratory and used a 

generic distributed system prototyping platform to realize the data network. This report presents the results of the hardware 

susceptibility threshold characterization which examined the dependence of measured susceptibility on factors like the 

frequency and modulation of the radiation, layout of the physical nodes and position of the nodes in the test chamber. The 

report also includes lessons learned during the development and execution of the experiment. 

15. SUBJECT TERMS

Avionics; Data network; High-intensity electromagnetic field; Resilience; Safety

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