Which GA-35 antenna is connected to GIA63W #2?

Any DA40 related topics

Moderators: Rick, Lance Murray

Post Reply
User avatar
MarkA
3 Diamonds Member
3 Diamonds Member
Posts: 92
Joined: Mon Aug 23, 2010 4:58 am
First Name: Mark
Aircraft Type: DA40
Aircraft Registration: N123MZ
Airports: KHIO
Has thanked: 57 times
Been thanked: 68 times

Which GA-35 antenna is connected to GIA63W #2?

Post by MarkA »

How can I figure out which GPS GA-35 antenna is connected to GIA63W #2 and which one is connected to GIA63W #1?
Attachments
IMG_20220112_161833558.jpg
User avatar
mhoran
3 Diamonds Member
3 Diamonds Member
Posts: 111
Joined: Fri May 23, 2014 11:56 pm
First Name: Matt
Aircraft Type: DA40
Aircraft Registration: N269RB
Airports: KLDJ
Has thanked: 26 times
Been thanked: 50 times

Re: Which GA-35 antenna is connected to GIA63W #2?

Post by mhoran »

There is a procedure in the maintenance manual: cover one antenna and see which GIA drops out. Of course, you probably can't do that as effectively in the hangar.

i appreciate that you also have one new antenna and one old antenna. I thought this was my plane for a second.
User avatar
Boatguy
5 Diamonds Member
5 Diamonds Member
Posts: 908
Joined: Mon Jan 22, 2018 4:48 am
First Name: Russ
Aircraft Type: DA40NG
Aircraft Registration: N454M
Airports: KSTS
Has thanked: 486 times
Been thanked: 585 times

Re: Which GA-35 antenna is connected to GIA63W #2?

Post by Boatguy »

With the hangar doors open I get pretty good GPS reception. Certainly good enough to tell which one is covered up.
User avatar
MarkA
3 Diamonds Member
3 Diamonds Member
Posts: 92
Joined: Mon Aug 23, 2010 4:58 am
First Name: Mark
Aircraft Type: DA40
Aircraft Registration: N123MZ
Airports: KHIO
Has thanked: 57 times
Been thanked: 68 times

Re: Which GA-35 antenna is connected to GIA63W #2?

Post by MarkA »

Thanks for the suggestions.

I pulled the plane out of the hanger this afternoon and turned one GIA63W on at a time then covered each antenna separately with a "fool proof GPS shield" (below) :). I then looked at the satellite signal AUX page to see which antenna was active.

In my case, it was clear the pilot side GA-35 is connected to GIA63W #1 and the passenger side is connected to GIA63W #2.
Attachments
2021-01-14 two pan psngr covered (17).jpg
User avatar
Steve
5 Diamonds Member
5 Diamonds Member
Posts: 1580
Joined: Thu Aug 12, 2010 1:23 am
First Name: Steve
Aircraft Type: DA40
Aircraft Registration: N432SC
Airports: 1T7
Has thanked: 53 times
Been thanked: 311 times

Re: Which GA-35 antenna is connected to GIA63W #2?

Post by Steve »

Mark: Don't let your wife find out that you are using her "tools". ;)
User avatar
Hooker
1 Diamond Member
1 Diamond Member
Posts: 2
Joined: Sat Feb 23, 2019 8:56 pm
First Name: Troy
Aircraft Type: DA40
Aircraft Registration: N969GL
Airports: KBNO

Re: Which GA-35 antenna is connected to GIA63W #2?

Post by Hooker »

Mark

Are you still having issues with your GPS reception?

I had similar issues 1 year ago with a GA35 antenna on my 2010 DA40 XLS. My GPS2 antenna was yellowed like your GPS1 antenna. There was an issue when the mount bolts are over torqued, it turns the GA35 into a transmitter. The intermittent problem would disable both GPSs. The simple fix is reducing the torque on the mounting bolts. Garmin has since redesigned the GA35 to be more resistant to this issue.

I have not had GPS1 fail since, however I am still troubleshooting intermittent reception with GPS2. A new GA35 did not fix the issue.
User avatar
MarkA
3 Diamonds Member
3 Diamonds Member
Posts: 92
Joined: Mon Aug 23, 2010 4:58 am
First Name: Mark
Aircraft Type: DA40
Aircraft Registration: N123MZ
Airports: KHIO
Has thanked: 57 times
Been thanked: 68 times

Re: Which GA-35 antenna is connected to GIA63W #2?

Post by MarkA »

Tory,

Thanks for sharing your experience - it sounds similar to mine.

In my case, I've been having intermittent loss of all GPS signal on the G1000 - it has happened about 3 times in the last 20 or so flights over the past 5 months. The problem did not reliably reproduce itself until last week when it started happening more often. After some additional test flights, log analysis, and testing the GPS antenna outside the hangar, I've concluded that the GPS2 GA-35 antenna (the white one on the passenger-side on my plane) has a hardware problem.

During the tests outside the hangar, I reset the circuit breaker on one GIA63W at a time and booted the system. The first thing I noticed was that GPS1 reliably connects to the satellites in about a minute after it's powered on whereas GPS2 takes 3+ minutes to get connected . The satellite signal strength AUX page also displays more satellites with stronger signals for GPS1 vs GPS2.

With the "two pot" metal shield on GPS1's antenna, GPS1 continued to connect to the satellites in 3DDiff resolution even though the signal strength as expected was reduced by the metal shield. In contrast, as soon any metal is placed over GPS2's antenna, the signal level for all satellites immediately drops to zero and GPS2 reverts back to "acquiring" mode for 3 or 4 minutes again.

I also reproduced the problem on the ground where GPS1 was connected and working fine when I closed the circuit breaker on GIA63W #2 and shortly thereafter both GPS1 and GPS2 lost signal for all satellites. In that case, both GPSs went back into acquiring mode. This seems to be an indication that the GPS2 antenna had turned into a transmitter problem you mention earlier.

I found several internet articles that describe this problem where a GA-35 antenna can sometimes fail and start oscillating and generating RF interference that effectively jams any other nearby GPS antennas. One of the causes is over torqueing the mounting bolts that may damage the internals as described in the following responses posted by Trek Lawler at Garmin:

“… In short what was happening is the ground plane was coming loose from the internal circuit board in the GA-35 unit and it was turning from a receiver to a transmitter oscillating at its tuned frequency of 1.575 GHz which as you now know is the frequency of the GPS data. We went through a couple of different shell changes with the vendor and did change to a different material that is intended to be more robust and less susceptible to the cracking if the screws are overtightened, plus there is also a big notice in the packaging about the max tightening of the fasteners in the package that has to be removed before you can install the new antenna.”

Sooo... my plan is to replace the GPS2 GA-35 antenna. I just received a new one today and it is scheduled to be installed later this week. I'm hopeful this will fix my problems but we will see. I'll let you know what I find out.
Post Reply