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Garmin GNS430 Nav board repaired twice

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andre.beusch(at)bluewin.c
Guest

Posted: Sun Dec 10, 2006 1:45 pm Post 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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bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Tue Dec 12, 2006 5:00 am Post subject: Garmin GNS430 Nav board repaired twice

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

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

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