In spite of being a member of the Europa Club since its birth I am a
newcomer on the forum-scene.
What prompted me to enter this scene is interference problems twixt my
Skymap IIIC and my KX125 radio.
Similar problems, I can see from browsing the archive-index, have been
discussed between Bryan Allsop and
Fred Fillinger a year ago, but there is some mysterious (to me)
variation in my case which I hope that Bryan or someone else
might be able to advise me about. But, please, slowly. I'm extremely
dim-whitted.
The problem, a chainsaw-like noise in the headphones when the GPS is on,
presented itself already in the distant past
with a Skymap-I, mounted in my Pa28. The solution was easy: I sold the
Piper, GPS included. Then built my present Europa
in which I mounted a Skymap II. All was bliss, until the noise after 3-4
years recurred. Yes, after 3-4 years! And only on some
frequenses, 119.52 where the interference was in bursts, and 118.5 (
and a few others), where the noise was continuous.
The Skymap II was then replaced by the IIIC. Ah, peace and quiet again -
for a while- until the problem recurred. First on the
old 119,25 (my home base), then increasingly on many other frequenses,
predominantly in the lower half range.
As with Bryan receiving and transmitting cancels out the noise more or
less, but not intercom, and it is absolutely enough to
render you insane and deaf. The interference also vanishes when the GPS
is removed from the panel and strapped to my
thigh, but that is a bit awkward.
The antenna line to the GPS runs from the spine of the Europa forwards
under the left door to the panel, and the one to the
Radio along the right hand side of the aircraft. The antenna coax to the
radio (and the TXP) are rather long and are coiled-up
inside the right hand side of the panel. Further, it doesn't matter
whether I use the fixed antenna or a loose one on top of the
panel.
My friendly avionics Wizart at Billund has after much head-scrtatching
applied a choise of his wizardry to the problem:
Making sure that connections on the GPS-coax are OK, even surrounded
said connection with some foil-like screening-material,
decreasing the squelch of the radio, applying some ferrite-pearls on
the individual leads of the power-lead to the GPS, all to
no avail. He has also expressed thoughts about some electronic component
in the GPS being ailing after some years' use.
The owner of a neighbouring helicopter-company whose helicopters use the
Skymap IIIC too, had the same problem which,
so he told me, was found to originate from the blower in the GPS due to
Worn bearings. Be that as it may, the Skymap I and
II do not have blowers, and were still beset with the problem!
It may well be an antenna/screening problem. But why does this problem
arise after a some years' impeccable service, and
then seem to increase?
Can anybody help with an explation which even I might grasp, and a
solution?
Niels Kock,
Odense, Denmark
OY-ODA
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