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andre.beusch(at)bluewin.c
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 Posted: Sun Dec 10, 2006 1:45 pm Post subject: Garmin GNS430 Nav board repaired twice |
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I have a Garmin GNS430 in my Glasair Super II.
The comm is connected to a dipole antenna in the vertical stabilizer,
the nav is connected directly (no splitter) to the dipole antenna in the
horizontal stabilizer.
Both are the antennas that were provided by Stoddard Hamilton, the kit
manufacturer, and were installed as per the instruction manual. The
antennas perform well.
Both times, the VOR/LOC lost 30 dB of sensitivity, apparently the input
stage was destroyed.
The first repair cost me about $1000, the second was warranty.
I wonder if someone had this problem with any kind of nav receiver.
Garmin said that it could have been overloaded by the comm transmission
because the antennas are to close to each other.
(they don't say anything about this in the installation manual)
Many people use a splitter for NAV/glideslope, so their receiver gets
less signal and would perhaps not be exposed to this problem.
As an electronics engineer, I'd like to understand this and will make a
measurement of the power that actually gets in the Nav receiver. I have
a 250 MHz oscilloscope for that.
This nav receiver should pass RTCA DO-196, if someone has these
documents handy, I'd be interested to see what the damage input power
should be.
I also consider putting a 6dB attenuator or an RF limitter on the Nav
antenna input.
Any opinions?
Thanks, --Andre Beusch
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bakerocb
Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA
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| Posted: Tue Dec 12, 2006 5:00 am Post subject: Garmin GNS430 Nav board repaired twice |
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12/12/2006
Hello Andre, I am trying to better understand your antenna connections.
You wrote: "The comm is connected to a dipole antenna in the vertical
stabilizer,
the nav is connected directly (no splitter) to the dipole antenna in the
horizontal stabilizer."
The GNS 430 box has two separate inputs for VHF nav and glide slope. As you
say this is frequently done by using one VHF nav antenna and then splitting
that input just before it enters the GNS 430 box.
When you say that your nav is connected directly (no splitter) to the
antenna does that mean that you are also feeding the glide slope input
directly from some separate glide slope antenna?
What is the status of the unit now? You have it back repaired and are not
using it for concern over damaging it again with comm transmissions or ---?
Comant industries has a wide array of couplers that you might consider using
to combine and or split inputs to your GNS 430 from nav / glide slope
antennas in order to protect the input stages from excessive comm
transmission inputs.
http://www.comant.com/home.cgi?ua=sgroup&crit=Couplers/Diplexers/Combiners
OC
| Quote: | Time: 01:45:56 PM PST US
From: =?ISO-8859-1?Q?Andr=E9_Beusch?= <andre.beusch(at)bluewin.ch>
Subject: Garmin GNS430 Nav board repaired twice
I have a Garmin GNS430 in my Glasair Super II.
The comm is connected to a dipole antenna in the vertical stabilizer,
the nav is connected directly (no splitter) to the dipole antenna in the
horizontal stabilizer.
Both are the antennas that were provided by Stoddard Hamilton, the kit
manufacturer, and were installed as per the instruction manual. The
antennas perform well.
Both times, the VOR/LOC lost 30 dB of sensitivity, apparently the input
stage was destroyed.
The first repair cost me about $1000, the second was warranty.
I wonder if someone had this problem with any kind of nav receiver.
Garmin said that it could have been overloaded by the comm transmission
because the antennas are to close to each other.
(they don't say anything about this in the installation manual)
Many people use a splitter for NAV/glideslope, so their receiver gets
less signal and would perhaps not be exposed to this problem.
As an electronics engineer, I'd like to understand this and will make a
measurement of the power that actually gets in the Nav receiver. I have
a 250 MHz oscilloscope for that.
This nav receiver should pass RTCA DO-196, if someone has these
documents handy, I'd be interested to see what the damage input power
should be.
I also consider putting a 6dB attenuator or an RF limitter on the Nav
antenna input.
Any opinions?
Thanks, --Andre Beusch
|
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