GPS failures

Regarding portable GPS devices....

I did a liitle searching around in regards to GPS interference. I am finding that the G296 is fairly unreliable in congested airspace. I've had episodic failures over LAX, and in the South Bay with repeated episodes of signal loss near RHV. The outages are complete and typically 1 to 2 minutes in duration. Almost never occurs in the boonies. Curiously my panel mounted Apollo GPS seems much less problematic.

It appears that these units are suseptible to radio interference (this is Garmin's explanation).

Sooo....I'm curious, are you guys using portables and if so are you having this kind of trouble?

Jeez

Antenna Dependent?

For me, it depends on the antenna I'm using. I got two portable antennas with my 396 - a small one and a tiny one. When I am using the small one, I have not had any problems. When I use the tiny one (sorry for the vague descriptions - I don't have them here at home....), I lose lock every single time I flew by the big antenna farm on the southwest side of Houston (Missouri City). Never had a problem elsewhere.

Paul

I've flown in between the Cedar Hill antenna farms with the stock (little 2" stick) antenna on my 296 without any signal outage.

Did have an outage once flying near the large antenna north of Reklaw.

Been flying for a couple of years all over Texas and the DFW area, including the Cedar Hill towers, with my 296 and never lost signal. Of course, now that I've said that..........

My luck

Yea I have never lost a signal but there are notams for GPS.

s_tones said:

I did a liitle searching around in regards to GPS interference. I am finding that the G296 is fairly unreliable in congested airspace. I've had episodic failures over LAX, and in the South Bay with repeated episodes of signal loss near RHV. The outages are complete and typically 1 to 2 minutes in duration.

[...]

Sooo....I'm curious, are you guys using portables and if so are you having this kind of trouble?

Click to expand...

in the little flying I've done in South Bay a few months ago with my 296, I have never lost lock, and I've been flying quite a bit in every direction around RHV since I was preparing my single-engine commercial checkride and needed spots for my eights on pylons, chandelles and lazy eights...

I've always used the suction cup antenna in every flight, and found it quite reliable.

Could it be that your airplane has a spurious emission coming from another piece of avionics that interferes with the GPS? Maybe it's a local oscillator harmonic that you get when you tune a specific frequency on your COM or NAV, who knows...

Ciao, Luca

GPS Signal Dropping

The new owner of my Cherokee contacted Garmin about the 496 losing it's signal. They told him that it's a known issue with some radios, that certain frequencies will jam the GPS signal. One of the radios on the list is the mk12d, which is the nav/com2 in that airplane.

So instead of an outside signal causing the problem, it might be something in your cockpit.

DBone said:

The new owner of my Cherokee contacted Garmin about the 496 losing it's signal. They told him that it's a known issue with some radios, that certain frequencies will jam the GPS signal. One of the radios on the list is the mk12d, which is the nav/com2 in that airplane.

So instead of an outside signal causing the problem, it might be something in your cockpit.

Click to expand...

That's very interesting. The one time I lost signal with my Garmin 296 I was flying with a Mark 12D in the panel.

CraigH@KRPH said:

That's very interesting. The one time I lost signal with my Garmin 296 I was flying with a Mark 12D in the panel.

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ah! Then, without knowing, looks like I was right!

Well, what can you expect from "Not A Radio COmpany"...

Ciao, Luca

P.S. Just kidding, don't mean to offend all of the many happy NARCO users out there.

thanks ya'll

Thanks for the input on this.
Not sure what the deal is. I've got the antenna on the glare shield.
It's about 2 feet from my PCAS device. Maybe an issue?
I'm gonna try a higher gain antenna or, if possible, hooking into my external GPS antenna (which currently serves my SL60 GPS).

Jeez

s_tones said:

Not sure what the deal is. I've got the antenna on the glare shield.
It's about 2 feet from my PCAS device. Maybe an issue?

Click to expand...

PCAS is a purely passive system, as far as I know, but since a receiver inherently has a small transmitter on board (its local oscillator), it could very well be that some spurious signal interferes with the 296.

Have you tried to turn off the PCAS and see if the 296 still loses lock? That is a good indication on whether there is an interaction between the two systems.

I'm gonna try a higher gain antenna or, if possible, hooking into my external GPS antenna (which currently serves my SL60 GPS).

Click to expand...

be careful when doing this kind of stuff! GPS antennas are typically powered by the receiver thru a phantom power (normally 5V, but 3.3V is more and more common), and you can't simply split the signal without taking care of the DC coming from the other receiver.

I've bought for real cheap at Radio Shack a satellite TV splitter and a DC block connector, and it works fine. Actually it's a 4-to-1 unit, so I can hook up up to 4 GPS, and of course I need 3 DC blocks to filter the DC from the secondary GPS receivers. Unfortunately the unit has F connectors, so I had to also connect a few F-to-BNC connectors, but it was a simple task.

This is setup is not flying yet, I am planning on installing it on my Pipistrel Virus sometimes in the future, to share the Garmin antenna with a Bluetooth GPS that I will hide behind the panel, so I can use stuff like PocketFMS easily in my cockpit.

Ciao, Luca

396 Lost Signal

While bringing my plane home to Calif. from New York my new 396 lost signal three times and all 3 were crucial.
I kept the stick antenna handy the second day and used it when signal was lost. When I got home I told Garmin and they sent me a new antenna. Problem solved.

It's never happened to me in the air despite a few years of regular use - but my 196 loses it's mind in my pickup everytime I put my truck radio (factory 2006 Chevrolet) into AM mode. FM and XM - no problem, but AM wipes it out completely every time. Must be the IF oscillator in the radio. Even having the radio in AM mode and pushing the on/off button still keeps the GPS out of lock, though you aren't actually powering down the radio by doing that, just stopping the audio output. It does this with both the stick and remote antenna, and the effect disappears about 5-6 feet from the pickup.