Garmin 430W problem

Pa28-140

Pa28-140

Pre-takeoff checklist
Joined
Dec 6, 2009
Messages
192
Location
Kansas City suburb
Display Name
Display name:
Gordon Shumway
This is going to sound crazy, but please bear with me. I had a Garmin 430W installed in my Cherokee. Also installed a cooling fan and new WAAS antenna. I have tested it on numerous GPS approaches. Between 12-7 miles from my home airport (OJC) I lose all GPS signal. When I am within a mile or two of my airport the signal begins to come back and by the time I am on the ground it's all good. Note: I can fly any and all LNAV GPS approaches at my surrounding airports. I have tested this at least 20 times and the result is the same. I borrowed a non-WAAS Garmin 430 and no problems. The avionics shop has never seen this before. Nobody else at OJC is having this problem. What is going on and what do I do now? Thanks, but frustrated.
 
High probability your WAAS antenna is bad. Known issue.
 
Does it happen only at that airport? Happen to have an older ELT installed?
 
If it's happening only in one place I think your getting interference from some ground based transmitter in that area. The first thing I would do is remove the ELT IAW FAR 91.207(f)(10) then fly the airplane in that same area and verify it is or isn't the ELT.

Here is an example of what ELTs are known to do. It just may be that it's wiping your gps signal.

https://www.pilotsofamerica.com/community/threads/heres-one-for-all-the-experts.96675/

If it's not the ELT causing it, then I'd look at the com radio connected to the com antenna nearest the WAAS antenna, and disconnect it and go flying.
 
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What do other GPS receivers without external antennas do in the same location?
 
bnt83 said:
If it's happening only in one place I think your getting interference from some ground based transmitter in that area. The first thing I would do is remove the ELT IAW FAR 91.207(f)(10) then fly the airplane in that same area and verify it is or isn't the ELT.

Here is an example of what ELTs are known to do. It just may be that it's wiping your gps signal.

https://www.pilotsofamerica.com/community/threads/heres-one-for-all-the-experts.96675/

If it's not the ELT causing it, then I'd look at the com radio connected to the com antenna nearest the WAAS antenna, and disconnect it and go flying.
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At only one location?? Good everywhere else.
 
Pa28-140 said:
Probably an older ELT, but not transmitting. How can that interfere at only one location?
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A high powered ground based radio station, such an FM radio station you listen to in your car. You fly close enough to it that the ELT antenna picks it up and that radio frequency energy mixes with the ELT circuitry and gets reflected out in an unpredictable manner. It could wipe out all kinds of things including GPS or com frequencies.

Takes 10 minutes to remove the ELT and go test fly... A lot cheaper that replacing a $300 WAAS antenna that may not be bad.
 
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Pa28-140 said:
Two different antennae. Good everywhere else except my home base.
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That supports the hypothesis that existing equipment in your airplane is not playing well with the 430w while you fly near some ground radio station in that area.
 
1. Mount the antenna as close to level as possible with respect to the normal cruise flightattitude of the aircraft. If the normal flight attitude is not known, substitute the waterline,
which is typically referenced as level while performing a weight and balance check.

2. The GPS antenna should be mounted in a location to minimize the effects of airframeshadowing during typical maneuvers. Typically mounting farther away from the tailsection reduces signal blockage seen by the GPS antenna.

3a. The GPS antenna should be mounted no closer than two feet from any VHF COM antenna
or any other antenna which may emit harmonic interference at the L1 frequency of 1575.42
MHz. An aircraft EMC check (reference VHF COM interference check in Post Installation
Checkout procedures) can verify the degradation of GPS in the presence of interference
signals. If an EMC check reveals unacceptable interference, insert a GPS notch filter in
line with the offending VHF COM or the (re-radiating) ELT transmitter.

Note: When mounting a combination antenna (ex. GPS and COM, GPS and XM),
recommended distance of two feet or more is not applicable to the distance between the
antenna elements provided the combination antenna is TSO authorized and has been tested
to meet Garmin’s minimum performance standards.

3b. The GPS antenna should be mounted no closer than two feet from any antennas emitting
more than 25 watts of power. An aircraft EMC check can verify the degradation of GPS in
the presence of interference signals.

3c. To minimize the effects of shadowing at 5° elevation angles, the GPS antenna should be
mounted no closer than 6 inches (edge to edge) from other antennas, including passive
antennas such as another GPS antenna or XM antenna.
 
Something on the ground is triggering the interference. It may be direct or indirect by exciting your ELT. You can remove your ELT antenna and conduct a flight test to see if the problem is still there. Monitor the satellite page. Interference will show the satellite signal bars diminish or disappear all together.

You can also see if you are getting interference from one of your Com units. Watch the satellite page and key the mike for 25 seconds or so on frequencies in the vicinity of 121.2 +/- .25 MHz and 131.3 +/- .25 MHz. If keying the mike causes the GPS bars to collapse and not immediately restore to a good signal, then your com unit is interfering with the GPS and you need to get this resolved.
 
What shop are you working with on your install? I'm familiar with a few of the local ones.
 
Everyone is hung up on the ELT. The interference may simply be ground based and directly on L1, too. There's ways to find out. Usually based on grabbing a directional antenna, appropriate filters, and a spectrum analyzer, and going for a drive near the area.
 
denverpilot said:
Everyone is hung up on the ELT. The interference may simply be ground based and directly on L1, too. There's ways to find out. Usually based on grabbing a directional antenna, appropriate filters, and a spectrum analyzer, and going for a drive near the area.
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When no other pilots at his home airport are reporting problems?
 
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I believe somewhere in the installation instructions for the 430W there is a reference to possible interference from legacy 121.5 ELTs. I was told about it, was skeptical and later found it in the documentation. The advice I got was go to a 406Mhz ELT.
 
denverpilot said:
And where is this magical place where all the complaints are collected for correlation? Here on PoA? ROFL...
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Pa28-140 said:
I can fly any and all LNAV GPS approaches at my surrounding airports. I have tested this at least 20 times and the result is the same. I borrowed a non-WAAS Garmin 430 and no problems. The avionics shop has never seen this before. Nobody else at OJC is having this problem.
Click to expand...
 
It's certainly most likely it's on board the aircraft. That's how tiny annoying RF interference works. The closer to it you are...

Mount all the antennas and the exact same radios on an identical airframe and see how that does -- if you're worried about figuring out if it's a malfunctioning part on only one airframe.

Here's the operations engineer in me talking: You're going to have to do or change something to find it. :-)

(From the guy who's been hunting an RF interference source somewhere near particular location for roughly ten years... I can tell you what it isn't! But we haven't found what it is, yet. It'd be a lot easier to change the receiver frequency at that location or place the receivers elsewhere, but one isn't easily done for various reasons, and the other was cost-and-time-prohibitive until the relatively recent advent of VOIP transport in voted receiver systems... So Door #2 is likely to finally be taken...)
 
John Collins said:
Something on the ground is triggering the interference. It may be direct or indirect by exciting your ELT. You can remove your ELT antenna and conduct a flight test to see if the problem is still there. Monitor the satellite page. Interference will show the satellite signal bars diminish or disappear all together.

You can also see if you are getting interference from one of your Com units. Watch the satellite page and key the mike for 25 seconds or so on frequencies in the vicinity of 121.2 +/- .25 MHz and 131.3 +/- .25 MHz. If keying the mike causes the GPS bars to collapse and not immediately restore to a good signal, then your com unit is interfering with the GPS and you need to get this resolved.
Click to expand...
Thanks John. I'll certainly give the ELT issue a try and also keying the other com. Did not have any issues when I tried a non-WAAS replacement 430. My shop now has another WAAS 430 for me to try. Will post updates.
 
Pa28-140 said:
Higginsville Avionics Lab
Click to expand...

If all else fails, you might consider having Kings (Butler) look at it. I've had my issues with them, but I think they've got a little deeper bench than Higginsville does. Don't get me wrong, I've used Higginsville and like them, but in some instances there is something to be said for having a larger staff with varied experience, etc.
 
bnt83 said:
That supports the hypothesis that existing equipment in your airplane is not playing well with the 430w while you fly near some ground radio station in that area.
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Could be, but the the various initial approach fixes where the GPS fails are 20+ miles apart. On the ground at home airport the signal is strong and reliable.
 
bnt83 said:
1. Mount the antenna as close to level as possible with respect to the normal cruise flightattitude of the aircraft. If the normal flight attitude is not known, substitute the waterline,
which is typically referenced as level while performing a weight and balance check.

2. The GPS antenna should be mounted in a location to minimize the effects of airframeshadowing during typical maneuvers. Typically mounting farther away from the tailsection reduces signal blockage seen by the GPS antenna.

3a. The GPS antenna should be mounted no closer than two feet from any VHF COM antenna
or any other antenna which may emit harmonic interference at the L1 frequency of 1575.42
MHz. An aircraft EMC check (reference VHF COM interference check in Post Installation
Checkout procedures) can verify the degradation of GPS in the presence of interference
signals. If an EMC check reveals unacceptable interference, insert a GPS notch filter in
line with the offending VHF COM or the (re-radiating) ELT transmitter.

Note: When mounting a combination antenna (ex. GPS and COM, GPS and XM),
recommended distance of two feet or more is not applicable to the distance between the
antenna elements provided the combination antenna is TSO authorized and has been tested
to meet Garmin’s minimum performance standards.

3b. The GPS antenna should be mounted no closer than two feet from any antennas emitting
more than 25 watts of power. An aircraft EMC check can verify the degradation of GPS in
the presence of interference signals.

3c. To minimize the effects of shadowing at 5° elevation angles, the GPS antenna should be
mounted no closer than 6 inches (edge to edge) from other antennas, including passive
antennas such as another GPS antenna or XM antenna.
Click to expand...
Wow! Sorry, but a lot of this is over my head. I do understand 3b and 3c and the location of the antenna is in compliance with those specs.
 
A lot of good responses. Some of it over my head but I will pass along to the avionics shop. They now have a loaner 430W they want me to try. Needless to say, if this one works fine then the problem is probably in my unit. I will post results. Thanks!
 
bradg33 said:
If all else fails, you might consider having Kings (Butler) look at it. I've had my issues with them, but I think they've got a little deeper bench than Higginsville does. Don't get me wrong, I've used Higginsville and like them, but in some instances there is something to be said for having a larger staff with varied experience, etc.
Click to expand...
Maybe. Mixed results with Butler in the past. Only sure thing is my wallet is a lot lighter when I leave. Gonna try the loaner 430W tomorrow. If all is well, then have to believe that it is my unit. Probably the next step would be to send it to Garmin. Will definitely have a thin wallet if that happens.
 
kontiki said:
I believe somewhere in the installation instructions for the 430W there is a reference to possible interference from legacy 121.5 ELTs. I was told about it, was skeptical and later found it in the documentation. The advice I got was go to a 406Mhz ELT.
Click to expand...
If this is the issue I guess the big question is why is it only an issue for one airport. ???
 
kontiki said:
I believe somewhere in the installation instructions for the 430W there is a reference to possible interference from legacy 121.5 ELTs. I was told about it, was skeptical and later found it in the documentation. The advice I got was go to a 406Mhz ELT.
Click to expand...
If this is the issue I guess the big question is why is it only an issue for one airport. ???
 
Pa28-140 said:
If this is the issue I guess the big question is why is it only an issue for one airport. ???
Click to expand...

Because there might be a specific radio source that is radiating near your airport, and that radio source may be getting into the antenna on the 121.5 ELT. And it may only be an issue for your aircraft because of the specific way your aircraft and the legacy ELT are set up.
 
The one takeaway up in the clip from the Garmin document is that there are notch filters that can help if it's the ELT or the Comm radio reradiating a mix that they shouldn't.

Downside is, most notch filters have insertion losses, so if installed on an ELT antenna system, the ELT will be weaker. Same issue with the Comm radio, actually.

The "snipping the ELT antenna" length shorter trick also may decrease the effective range of the ELT by quite a lot.

The good news is, hardly anyone is listening for 121.5 ELTs anymore. Haha.

Losing 3dB to filter insertion loss probably isn't the end of the world on the ELT with nobody really listening much for them anymore, anyway. Losing 3dB on the Comm would likely be slightly more annoying more often, but only at long ranges from the ATC antenna sites.

But if a specific comm radio or the ELT are suspects, it's at least easy to try out and test with. They just plug in via standard RF connectors in-line pigtailed on to th resisting coax at the radio end.
 
Pa28-140 said:
If this is the issue I guess the big question is why is it only an issue for one airport. ???
Click to expand...

The worst offender I have first hand experience with was a old old old (in nice shape) KX155 that was messed up by an Amerking AK450 ELT (older 121.50 only version). The noise was so bad from the ELT that while in the traffic pattern @ KLNK the squelch was almost always broken and constant static poring through. We went to the avionics shop twice and they found nothing wrong with KX155, even turned the squelch all the way up, then told us to remove the ELT on a test flight. That airplane did not have an onboard GPS so nothing to compare there. Replaced the ELT with a newer one and never had a problem again.

For whatever reason, its was only the Lincoln area triggering the problem. Makes me wonder if there I something wrong with the broadcasting stations (or whatever it is) that causes it.
 
Pa28-140 said:
This is going to sound crazy, but please bear with me. I had a Garmin 430W installed in my Cherokee. Also installed a cooling fan and new WAAS antenna. I have tested it on numerous GPS approaches. Between 12-7 miles from my home airport (OJC) I lose all GPS signal. When I am within a mile or two of my airport the signal begins to come back and by the time I am on the ground it's all good. Note: I can fly any and all LNAV GPS approaches at my surrounding airports. I have tested this at least 20 times and the result is the same. I borrowed a non-WAAS Garmin 430 and no problems. The avionics shop has never seen this before. Nobody else at OJC is having this problem. What is going on and what do I do now? Thanks, but frustrated.
Click to expand...

I'm going to be shooting some approaches into/around OJC tomorrow. If you'll give me a little better idea of where you're losing signal, I'll fly around that area to at least give you some piece of mind that it's not ALL 430Ws losing signal there.
 
bnt83 said:
For whatever reason, its was only the Lincoln area triggering the problem. Makes me wonder if there I something wrong with the broadcasting stations (or whatever it is) that causes it.
Click to expand...

Unlikely it's something wrong, just the perfect combination of frequencies. The "skirts" on a high power broadcast transmitter's signal, even when legally suppressed as much as they're supposed to be, are still a lot of RF signal compared to what most two-way radios are designed to receive. Mix those in an ELT with no output filters, and use the specific frequency the mix hits as the local approach control frequency...

A friend who now works for FCC always says, "Passive intermodulation is the devil's snack food."
 
denverpilot said:
A friend who now works for FCC always says, "Passive intermodulation is the devil's snack food."
Click to expand...

Amen to that. All it takes is one non-linear joint and away you go. The Navy really had (has?) a problem with this. Just imagine how many rusty joints you can have on a ship.

I maintained and upgraded a FORTRAN program back in the early 80s that performed intermodulation product analysis on systems of transmitters, receivers and antennas while I worked at Martin Marietta Denver Aerospace. NASA ran this program on all shuttle flights beforehand to see if there were likely to be any problems with the payload for a particular flight. I wasn't a ham back then, but I had the frequency the first ham on the shuttle was going to use (STS-9) as I had the data deck for that mission.
 
Ghery said:
Amen to that. All it takes is one non-linear joint and away you go. The Navy really had (has?) a problem with this. Just imagine how many rusty joints you can have on a ship.

I maintained and upgraded a FORTRAN program back in the early 80s that performed intermodulation product analysis on systems of transmitters, receivers and antennas while I worked at Martin Marietta Denver Aerospace. NASA ran this program on all shuttle flights beforehand to see if there were likely to be any problems with the payload for a particular flight. I wasn't a ham back then, but I had the frequency the first ham on the shuttle was going to use (STS-9) as I had the data deck for that mission.
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Owen Gariott. And the radio was the Intrinsically Safe version of the General Electric MP/A handheld, which had been space qualified.

I have three of them, VHF, UHF and 900 MHz. Reprogrammed to be front face programmable.

Great radios. You could also beat a suspect to death with one in a pinch, for the cop-shops that used them, and they'd sill work afterward. Haha.

I never managed to work a SAREX (Shuttle Amateur Radio Experiment) mission or get a QSL card. My CFI did. I'm still jealous. LOL.

I did make sure one of our local repeaters carried the Shuttle Comm audio for about a decade after the first audio feed location went away. We had it fed in such that if the repeater went active with a local QSO, it'd mute until they were done and then come back, except during launch and landing when we disabled the mute so doofuses kerchunking wouldn't mess it up for all of us listening.

Sure was fun listening to them do stuff. Way better drive-time entertainment than broadcast crap! I remember having enough time to listen to almost all of the audio of the Hubble spacewalks. Amazing stuff.
 
You can also get band pass filters for the GPS receiver, IIRC....
 
denverpilot said:
I never managed to work a SAREX (Shuttle Amateur Radio Experiment) mission or get a QSL card. My CFI did. I'm still jealous. LOL.
Click to expand...

Me, neither. But I do have a pair of QSL cards from working the MIR space station on 2m packet. 25 Watts into a J-pole antenna is all it took. :-)
 
Update: after installing a new antenna, cooling fan, data card and replacement 430W provided by Garmin, the loss of signal persisted. The last thing I tried (wish it had been the first) was to disconnect the ELT antenna. Voila! No more problem. Apparently something on the ground near my airport was combining with the ELT to cancel GPS signals to my unit. I don't get it, but guess it doesn't matter. Only hope the new ELT does not do the same thing. Thanks for all of the input. Never would have resolved the problem withou your help.
 
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