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GPS Antenna Failure(s)

K

KTOA

Member
Earlier this week I flew into Hailey, ID (KSUN) late one night. It's essentially tucked into a valley with high mountainous terrain on three sides surrounding it.

While on the visual approach 10 miles out, all three of my GPSs lost their signal. This includes the 530W, 430W, and the 696 which is mounted on the panel with velcro. Surprised...yes. Fortunately we were VFR and landed without issues.

On the ground, all three GPSs regained their signals. OK. Great. Intermittent problems are always easy to troubleshoot...

The next night, on approach into Willows, CA (KWLW), we again lost all three GPSs. Landed without issue in VFR conditions.

To get to the end of the story, the 530 antenna went south with a vengeance. It ended up sending out some kind of 'signal' that blanked out the other two antennas.

Could this have been an issue while on an approach while IMC? A strong YES. I have never heard of this scenario before so I'm just trying to get the word out of this being a possibility.

The antenna was approximately four years old from when we upgraded to WAAS. The avionics shop that made the repair had seen this scenario once before in a King Air. All the other approximately 30 antennas they have seen had just 'died' and stopped working.

Be careful out there.
 
Test

Check NOTAMs to see if GPS outages expected in that area. Sometimes govt conduct tests which play havoc to GPS. Having vor/ILS backup is nice sometimes.
 
The NOAA Space Weather observations only showed R0, S0, and G0 level activity over the last several days, so it doesn't look like a solar radiation event.
 
NOTAMS

The first thing I checked after each landing was any NOTAMS that I may have missed (yes I do read the NOTAMS prior to flying...). There was nothing published, including all the FAA/GPS/DoD sites I could find/check.

The offending 530W antenna was the root cause. Verified.
 
Please contact Garmin with your issue. I had similar issues and Garmin went out of their way to fix my problem. I am sure they are tracking these issues and would love to have all your details first hand.

Since they fixed me up and I later upgraded to the GTN650 (same antenna), all has been well.

This and other forums show a history of this issue going back several years with similar failure modes like you describe. Last I was told, it was mostly isolated to a certain range of antenna serial numbers which makes sense because reports of issues with the newer units are scarce.
 
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I did call Garmin tech and will report what they say.

Antenna
Model: GA 35
Garmin P/N: 013-00235-00
D.O.W: 07/10

I have the antenna in my possession. I did a quick attempt at opening it. No joy - denied. I strongly suspect it will be epoxied. Not that I have a clue of what I would be looking at. I will hold off in case Garmin wants it.
 
This happened to me once too. Surprisingly of all of the GPS receivers that I had in the aircraft only the one built into an iPad survived.

How did you verify that it was the 530 antenna? Is there a way to trigger the problem if it is intermittent?
 
The avionics shop needed to identify the problem antenna because the 530 & 430 antenna are adjacent to each other.

They covered the antenna with aluminum. That allowed the other antennas to see the satellites. After that, I covered the antenna with my hand and that had the same result. I should try the same hand covering experiment now that the new antenna is installed.

During each event my Blackberry (I know, I know) and my friend's Iphone GPSs were fully functional.
 
Same issue

I had the same issue but it was intermittent at first then became more frequent. One way I used to isolate it was to turn off GPS items one at a time, when you turn off the culprit you will see the signal strength on the other GPS units jump.

There seems to be some idea that people are tightening the antenna mounting screws too tight. I installed mine and I know they were torqued correctly. After trying all kinds of trouble shooting, Garmin replaced my antenna. So far so good and I have not had any issues.

Cheers
 
Go to fltplan.com and check the RAIM for the area you were in.
You might not had reliable signal coverage in that area.

Jack
 
RVG8tor said:
I had the same issue but it was intermittent at first then became more frequent. One way I used to isolate it was to turn off GPS items one at a time, when you turn off the culprit you will see the signal strength on the other GPS units jump.

There seems to be some idea that people are tightening the antenna mounting screws too tight. I installed mine and I know they were torqued correctly. After trying all kinds of trouble shooting, Garmin replaced my antenna. So far so good and I have not had any issues.

Cheers
Click to expand...

Was it your 430 or the X96 that had the faulty ant?
 
KTOA said:
I did call Garmin tech and will report what they say.

Antenna
Model: GA 35
Garmin P/N: 013-00235-00
D.O.W: 07/10

I have the antenna in my possession. I did a quick attempt at opening it. No joy - denied. I strongly suspect it will be epoxied. Not that I have a clue of what I would be looking at. I will hold off in case Garmin wants it.
Click to expand...

My main antenna mounted on the center of my RV-8 dash is a GA57 When I installed my GDL39 it had a GA25.

I wanted the dash to look clean so I mounted the GA25 immediately behind the bigger GA57.

I started to have all kinds of GPS reception problems! Once I moved them about a foot apart the reception was back to normal.

But it did wipe out reception just like you describe. I am glad Garmin eliminated the need for an antenna in the GDL39 ( if you use the GDU375 feed).
 
The explanation for this is pretty simple. GPS signal is tiny - like a speck of fly dirt in a pepper shaker. As a result, GPS antennas contain amplifiers. These amplifiers are powered by DC power fed up the center conductor of the coax.

If something goes wrong with the amp or the filter circuits around it, it can cause any number of problems. Often the amp will cause a broadcasting of electrical noise, and uses the actual antenna elements to radiate that noise. Any GPS antenna within a reasonable distance will be overwhelmed by that noise. Suddenly you go from having working to having non-working GPS receivers in your airplane. And it's only your airplane that will be effected.

This is a known issue with Garmin GPS antennas. Garmin should come good for replacement.
 
RVG8tor said:
I had the same issue but it was intermittent at first then became more frequent. One way I used to isolate it was to turn off GPS items one at a time, when you turn off the culprit you will see the signal strength on the other GPS units jump.

There seems to be some idea that people are tightening the antenna mounting screws too tight. I installed mine and I know they were torqued correctly. After trying all kinds of trouble shooting, Garmin replaced my antenna. So far so good and I have not had any issues.

Cheers
Click to expand...


I recently went through a similar ordeal with my GTN650. It started loosing satellites almost immediately after being airborne, but worked during taxi. I had one time where them came back when the wheels hit the pavement.

First check was to looking for wiring issues with the connectors. Problem still continued.

I then was told the same story about people over torqueing the screws and potentially cracking the case of the antenna. I know I didn't over torque the screws. I even got out a magnifying glass to look for minute cracks, found none.

I ordered a replacement GA-35 (mine was out of warranty), made the swap, and things have worked fine since. With all the recent reports, I'm wondering if Garmin just had a bad batch of antennas that are all failing with similar symptoms. I suspect there is no way to validate that speculation.
 
Likely internal oscillation

KTOA said:
The avionics shop needed to identify the problem antenna because the 530 & 430 antenna are adjacent to each other.

They covered the antenna with aluminum. That allowed the other antennas to see the satellites. After that, I covered the antenna with my hand and that had the same result. I should try the same hand covering experiment now that the new antenna is installed.

During each event my Blackberry (I know, I know) and my friend's Iphone GPSs were fully functional.
Click to expand...

A well known failure mode is that the LNA (low noise amplifier) begins to fail and starts to oscillate. The LNA has about 25 dB of gain and the antenna is a nicely tuned circuit ... this would make a nice low power transmitter that could jam other receivers via close by antennas. GPS is a very weak signal, and can be easily jammed with a weak in-band signal.

If the antennas are independent, you can isolate them by turning off the receiver that the offending antenna is connected to. The antennas are powered by a DC voltage on the antenna cable; if the receiver is off, there is no power. In this way, you could have isolated the bad boy, and the other receivers would have functioned normally.

This also argues for keeping the antennas far apart to minimize interference from this failure mode.
 
A hidden message is provide dedicated switchable power to your GTN - or any other box - that doesn't have an integral on/off switch. The lack of one on my 650 has proven an irritation at times, and this thread shows it's a necessity.

John Siebold
 
similar issue

with the GPS puck antenna that came with my Byonics tracker - co-located on the glareshield within inches of my Garmin 296 puck, the Garmin loses signal... moved to the baggage area window, everybody gets along well.
 
GPS Antenna failure

The same failure happened on my Garmin 430 antenna during actual IFR. It causes all nearby GPS antennas to be lose signal, including your iPad and handheld GPS. It took me a while to figure out that I had to power off the Garmin 430 to get my other GPS's to work. Fortunately I had a second radio. It is a known failure mode and there is a service bulletin.
 
430w

F1R said:
Was it your 430 or the X96 that had the faulty ant?
Click to expand...

Sorry I did not make it clear, it was my 430w antenna. I isolated it by turning all GPS to signal bar screen then I would turn off a GPS if nothing happens with the other signals I would turn it back on. When I turned off the 430W my 496 and GDL 39 signals instantly went from zero to normal strength.

Good Luck
 
In the last four flights I have lost gps signals twice. Both times my 430W and my 496 lost signals. I have had this installation in the aircraft for six years with no prior issues. I have contacted my avionics shop and they suggested that it sounded like a bad antenna. Next time it happens I will turn off the 430 and see if my trusty 10 year old 496 will come back.
This is a really BAD failure mode that it takes out your back up GPS. With both units out I fired up the ForeFlight on my iPad and got a signal with no problem.
My 496 antenna is on the glare shield. The 430 is mounted forward the firewall just under the top cowling. I wonder if heat has been a factor?
 
There is a youtube video someone took on-board quite a few years ago showing how a failed 430w's antenna would wipe out the other on-board gps signals. I didn't find that one readily, but here's another ground based video.
 
Garmin 430 GPS Failure w Dynon System

I am tagging on to this thread as it appears to be the latest discussion regarding Garmin 430 GPS failures and possible causes.

My situation: For three years and 280 hours I have had some very infrequent and short lived Garmin GPS failures. I have both the Skyview Dynon GPS antenna/receiver and the Garmin antenna mounted on top of the fuselage just behind the slider canopy on my RV9. They are approximately six inches apart. In the past month, the Garmin 430 is frequently unable to acquire satellite signal unless I turn the Dynon system off, let the Garmin acquire and then turn the Dynon system on. When the Dynon system is turned on it suppresses the reception of the Garmin 430. This is seen by viewing the satellite acquisition page on the Garmin. Note regarding the discussion above in this thread, there is no apparent degradation of Dynon GPS reception. My Garmin antenna is circa 2010.

Complicating the diagnosis, the problem occurred after replacing both ADHARS locate deep in the tail cone and replacement of a circuit board on one of my Skyview screens. Note that the suppression of the Garmin signals appears to be independent of which screen is on.

I have been advised by Garmin to move one or the other antennas, something that I'd rather not do, leaving five holes in my nicely finished fuselage. Especially since for an extended period of time I did not have a problem with my configuration. Garmin also suggested that perhaps the Dynon unit was failing and emitting more EMI than when originally installed.

With what I have come across in various threads I am pursuing the following in order of priority:

Replace Garmin antenna under the assumption that my existing antenna was produced during a period where know faulty antennas were produced.

Test with a replacement Dynon antenna, addressing Garmin's suggestion above.

Replace coax, which from discussions I have read seems an unlikely culprit. This assumes that the connection and/or shielding is faulty.

Check for other sources of interference, which could be adding to the Dynon interference; e.g., the replacement ADAHRS, voltage spiking from the alternator suggested in earlier postings.

Relocate one of the antennas.

I?d appreciate any suggestions that would help me identify and correct the situation.

John
 
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Although I am not suggesting this is the problem in your case, there is an area North of Naval Air Station Fallon (KNFL) where I almost always lose GPS lock. It is just west of a MOA and Prohibited area.
I get error messages on my Dynon, Garmin 560 and Ipad! Hmmm, think they may be influencing the signal?
 
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