GPS (Garmin) signal loss ... Seeking help

[jclark]

Not quite RV but ...

A friend of mine called to tell me he lost GPS signal to BOTH his Garmin 430 AND his Garmin 496.
(He was flying in a Bonanza ...metal like RV's )

Seems he experienced it after about 12 minutes of flight. They both came back eventually but it was clear to him that the GPS signal got "weaker and weaker" until there was none being "received". Not sure yet as to what caused it to come back. A series of tests will be done later but I figure I would appeal to this group for opinions. Some RV flyer MIGHT experience this one day as well.

Two points of note:
1. Plane recently waxed
2. Runway/taxiway recently repaired/"blacktopped"
And thus, there was a layer of wax and then a layer of "carbon" on the metal plane.

Has anyone in RV-land experienced this?

Any ideas as to what may have happened?

James

[flickroll]

A number of years ago while a flying a Beech A36 in OK I had a sudden and complete loss of GPS signal at about 4,000' agl. I could descend and get the signal back, then climb and lose it again. After a lot of test flying I could not figure out what was going on. Even called FSS to see if there was some sort of GPS signal degradation that day; there was not. Finally I called my avionics tech back in Virginia. He said....

Do you have a cell phone?

Yup

Is it turned on

Yup

Is it a Samsung model xxxx?

Yup

TURN IT OFF!!

I turned it off and the problem went away. Turns out when the phone went to high power mode at altitude (searching for a tower) it would swamp the receiver. This was on a UPS AT CNX80, but the tech said it happens to Garmin 430's too.

Don't know if this is the source of your problem but would be worth checking out.

[jclark]

Thanks.

I will check into this.

Any other ideas out there?

James

[bryan12]

while taking my captains license course in Charleston SC at Sea School. My instructor an x navy ship captain and longtime sea tow captain, told us that the pentagon will at-will and can reduce accuracy of the gps signal nationwide or in regions for reasons of national security. He said while in the channel on his sea tow boat on september 11th his regularly extremely accurate gps's were reduced dramatically in accuracy.

not really an answer to your question but something interesting to think about.

[cfiidon]

I starting flying in Florida a couple of years ago and noticed something new for me. Whenever I got withing five miles or so of television broadcast towers I would lose my Garmin 396 signal. It was consistent. Haven't seen it happen again since they went all digital, but then again I haven't really been close enough.

The point is that if you get close enough to an interference source the high power overwhelms the filters and there goes your signal.

Don

[airguy]

I cannot use my Garmin 196 in my truck with the antenna on the windshield if my truck radio is receiving an AM station. If I switch the radio to XM or FM, I get the GPS signal just fine, but there is some intermediate frequency generated within the radio in the AM mode that swamps my GPS receiver. I can switch the radio back and forth and watch the signal strength on the 196 fade in and out immediately. This is a 2006 model Chevy factory radio - I'd be curious to see if others can duplicate this.

[tomcostanza]

Here is a clip from a thread on the AeroElectric Connection's Matronics site.

There are a number of tests required in the Garmin installation
manual, including transmitting with each radio on the following
frequencies for 35 seconds, while watching the satellite reception
screen:

121.150, 121.175, 121.200, 121.225, 121.250
131.200, 131.225, 131.250, 131.275, 131.300, 131.325, 131.350

In my case the 131MHz frequencies interfered. Not just slightly, but
completely killed reception of all GPS satellites. The strength bars
went to zero immediately. The 430W required more than a minute to
recover after unkeying the transmitter.

The entire thread is here.

A nav/com can interfere with a GPS in transmit or receive mode. More info can be found here.

Please let us know if you find any more info.

Clear skies,

[vasrv7a]

A couple of other things to consider:

1. If the antenna cable is RG58, there could be an antenna cable issue. the correct GPS antenna cable to use is the RG400 or RG142 (both are amber in color). I had an issue a few years ago with RG58 and when I installed the other type of cable, the problem was solved.

2. The integrity of the antenna cable may have been compromised in some way. Have your friend check the cable from end to end.

Good luck.

Victor

[airman]

I have lost my 396 gps signal when tuning into certain vor frequencies. My antenna in on the dashboard.

Mike

[ScottHess]

Had a 496 in my Citabria with the antenna stuck on the greenhouse that would flatline (no bars at all) whenever I tuned to the ATIS (119.95) on my KY97. I moved the antenna 3 inches and it was fine. But then again that was a portable unit...