Evaluation Engineering - 18

MIL/AERO TEST

UTILIZING THE CAPABILITY OF THE VNA
FOR MIL/AERO MAINTENANCE AND
TROUBLESHOOTING
Identifying a new technical requirement on a program of
record is both a major headache for the program office
and a positive circumstance for engineers looking for a problem
to solve. As simple as it sounds, B-1 Integrated Battle Station
(IBS) was seeking a test methodology for locating deficiencies
in the digital video interface (DVI) cable runs between the
multifunction displays and the video processor. The application of a time-domain reflectometer to the problem was only
going to expose shorts and opens. More fidelity was needed
to characterize the DVI cable assembly in the cockpit-seeking
twists of twisted pair and minimum bend radius installation
issues. The treatment of the cable assembly (connectors, conductors, terminations) as a transmission line enables a wideband,
multiport S-parameter view of the problem, which opens up a
much more sensitive measurement. The challenge is to produce
test results in a repeatable, easy-to-understand GUI display that
will stand up to realistic environmental conditions.
At the core of any tester, there are three common, essential
functions: Power supply, display, and a single board processor.
All three require technical tradeoffs:
* Power supply must be robust to handle worst-case temperature and have switchable output elements for power
savings while the tester is on batteries. Additionally, a FET
bridge for output shorts-protection is a desirable feature.
Power supplies are literally the heart of the system and
typically don't receive much attention.
* Display should be LVDS sunlight-readable, color, capacitive touchscreen and rugged. HD displays are wonderful
for graphics, but the cost tradeoff isn't attractive for a test
tool. A 24-bit LVDS display simplifies the interface to the
single board computer without incurring excessive cost.
* Single board computer must be reliable with adequate
cache memory and expandable to host a wide variety of
USB-tethered modules. PMC is a reasonable form factor
(small and power
efficient) but a fullfunction single board
computer with LVDS
for the monitor and
mSATA hard drive
drives the design toward PC/104.

EVALUATION ENGINEERING AUGUST 2019

DragoonITCN

by Robert Appenzeller

PXI has been the standard for industrial and most military
test sets since VME went out of vogue (except with the Navy)
in the '90s. The backplane is rugged and there exists a wide
variety of functional modules that can be integrated. However,
reduced size, weight and prime power considerations drive test
tool designs into modular form factors. There will always be a
requirement for PXIe chassis, especially when creating new test
methods and analysis tools, but the small form factor testers
will increasingly be integrating functional blocks via USB and
PC/104 interfaces.
As the integration of tester capabilities grow beyond the basic
elements, specific requirements become apparent as the tester
design matures. For example, the insertion of high-frequency
digital video interfaces into existing aircraft platforms presents
a challenge to the test tool design effort. Beyond the basic "how
best to obtain quantifiable, repeatable results?"-the physical
reality of testing four pairs of shielded conductors efficiently
while maintaining a calibrated measurement environment
presents its own unique challenges. The block diagram below
depicts a common scenario where four channels need to be
independently analyzed with a novel hardware solution that has

DragoonITCN

Evaluation Engineering

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