Avionics News January 2018 - 31

CAPABILITY,
Tramper explained that because of
that difference, the industry standard
RG-58 coaxial cable won't work
well for ADS-B installations.
"Not many technicians realize
that," he said. "They see an aircraft
that already has good RG-58 in it, so
they pull out the Mode C and install
the Mode S transponder. When they
test it on the ground it works fine,
but then they find they have limited
range at altitude. All the manuals
state that you need to replace the
RG-58 with RG-400 coaxial cable,
but sometimes that step gets missed.
Another thing to look at are the
connectors themselves. Make sure
you always look up the specific loss
specifications for any connector you
use to terminate RG-400. Then factor
that into the total insertion loss for
the system."
Antenna system
troubleshooting
If you suspect an antenna
problem, other than checking the
connectors and the baseplate for
corrosion, there's not a lot you can
do with your standard tools.
"Technicians always want to put
an Ohm meter on the center pin and
read it to ground to see if they can
get a reading on how it is working,"
Jeckell said. "That doesn't help
at all in most cases. You need a
specialized antenna tester to see how
the antenna system is working."
According to Pacheco, sometimes
an antenna problem isn't an antenna
problem and is, in fact, a problem
with electrostatic noise or P-static.
"It is widely known that
electrostatic charging of the aircraft
in-flight generates radio frequency
noise, which disrupts navigation and
communication," he said. "This type
of charging can result from several
sources on the aircraft. When
P-static problems occur, they can be
difficult to trace."

Pacheco explained that the
"noise" can often be generated by
nonconductive devices such as
radomes, fiberglass winglets, and
other nonmetal panels, or an isolated
(unbounded) piece of metal, other
antennas, or static dischargers. You
can see why troubleshooting these
type of problem is a royal pain.
"As the aircraft charges, it reaches
a potential at which a spark jumps the
gap from aircraft structure to isolated
metal," he said. "The spark can
produce broadband noise extending
through 1,000 MHz. These trouble
spots are difficult to find because they
are usually hidden by paint, buried
inside the airframe and nonconductive
areas not coated with antistatic
material. Checking with ohmmeter
may be difficult because aluminum
joints can show a ground, but have
resistance to radio frequencies."
To help technicians get an
accurate look at what's happening
with today's every-increasingly
complex antenna systems,
Dayton-Granger has created the
DG Electrostatic Diagnostic Test
Instrument.
"It is used to electrically charge
an aircraft on the ground to simulate
the charging phenomena that
aircraft encounter during flight,"
Pacheco said. "This test instrument
can simulate streaming current
noise, sparking noise, and corona
noise, allowing the problem to
be identified so that corrective
measures can be taken to eliminate
those sources of electrostatic noise
on the aircraft being tested. To
locate this problem, the aircraft can
be probed with the EDTS set while
monitoring aircraft receivers for
arcing noise. When the noise area
is identified, physical identification
can isolate the piece of metal.
This can greatly lessen the effect
of environmentally-induced noise
while in-flight." q

GIS 25 years' experience provides
quality service of instruments, specializing in altimeters, panel mounted
and remote gyros, including:
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KEA-346
KVG-350
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RELIABILITY,
Experienced and trained technicians embody a dedicated focus to the customer
expectations that is key to GIS reliability
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enables efficient operations. A family atmosphere is fostered at GIS that insures
the shop runs as a team effort. It is reminiscent of what customers embraced in
the aviation industry years ago.

QUALITY.

Competitive prices, high-quality workmanship, quick turnaround time and
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GEORGETOWN
INSTRUMENT SERVICES
FAA CRS# GTNR482X
210 Airport Road * Taylor, Texas 76574

512-352-9000

www.georgetowninstruments.com
avionics news

*

january

2018

31
http://www.georgetowninstruments.com
Table of Contents for the Digital Edition of Avionics News January 2018
