GPS Mystery

[tony roberts]

Hi
I own a Garmin 196 GPS. When I turned it on today it would not find any
satellites. I took off and during the flight swithched it on and off
several times, unplugged and replugged the cables without success. I
landed at my destination and saw a friend who also owns a 196. I took
mine over to his aircraft, plugged it into his antenna and it worked
right away. So - faulty antenna right?
I went back to my plane, tested it again and it worked right away.
A while later I took off and it wouldn't work. I landed at my next
airport and shut down. I then tested the GPS and it worked fine.
Later I took off and it wouldn't work.
When I returned to my home airport I left the aircraft running and
swithched off all of the electrics and switched on the GPS and it
worked., then I started turning the electrics/electronics on one by one.
It kept working until I turned on the DME and then it lost satellite
reception. The DME was tuned to 109.5 - I don't know what that is - it
had been switched during the annual.
I turned off the DME, rebooted the GPS and it worked fine. Turned the
DME back on - the GPS lost reception. Then I turned the DME tuner up one
to 110.5 anfd the GPS worked fine. I tried it on several other settings
and it worked fine. Each time the DME was tuned back to 109.5 the GPS
lost its satellites.
Just thought I'd share that in case anyone has a GPS loss of reception
in flight. It could just be something as crazy as this.

Tony

--

Tony Roberts
PP-ASEL
VFR OTT
Night
Almost Instrument :)
Cessna 172H C-GICE

[J. Severyn]

"tony roberts" > wrote in message
news:nospam-AC03C5.18041801022004@shawnews...
snip
> Each time the DME was tuned back to 109.5 the GPS
> lost its satellites.
> Just thought I'd share that in case anyone has a GPS loss of reception
> in flight. It could just be something as crazy as this.
>
> Tony
>
> --
>
> Tony Roberts
> PP-ASEL
> VFR OTT
> Night
> Almost Instrument :)
> Cessna 172H C-GICE

Sounds like a harmonic of the DME receiver's local oscillator just happens
to be at the GPS frequency. GPS runs on very low signal-to-noise ratios, so
even a low-power source can swamp the GPS receiver. Thanks for the
heads-up. Hope I can remember it if the GPS seems to quit.

J. Severyn

[C J Campbell]

This sort of problem used to crop up much more frequently. Garmin has been
improving their software over the years so it is not as bad as it once was.
I had a 195 that would not work in several different aircraft when the
radios were on at all. A software update fixed that.

[tony roberts]

I now have the answer.

Check out - http://www.scn.org/%7Ebk269/gps.html

Tony



In article <nospam-AC03C5.18041801022004@shawnews>,
tony roberts > wrote:

> Hi
> I own a Garmin 196 GPS. When I turned it on today it would not find any
> satellites. I took off and during the flight swithched it on and off
> several times, unplugged and replugged the cables without success. I
> landed at my destination and saw a friend who also owns a 196. I took
> mine over to his aircraft, plugged it into his antenna and it worked
> right away. So - faulty antenna right?
> I went back to my plane, tested it again and it worked right away.
> A while later I took off and it wouldn't work. I landed at my next
> airport and shut down. I then tested the GPS and it worked fine.
> Later I took off and it wouldn't work.
> When I returned to my home airport I left the aircraft running and
> swithched off all of the electrics and switched on the GPS and it
> worked., then I started turning the electrics/electronics on one by one.
> It kept working until I turned on the DME and then it lost satellite
> reception. The DME was tuned to 109.5 - I don't know what that is - it
> had been switched during the annual.
> I turned off the DME, rebooted the GPS and it worked fine. Turned the
> DME back on - the GPS lost reception. Then I turned the DME tuner up one
> to 110.5 anfd the GPS worked fine. I tried it on several other settings
> and it worked fine. Each time the DME was tuned back to 109.5 the GPS
> lost its satellites.
> Just thought I'd share that in case anyone has a GPS loss of reception
> in flight. It could just be something as crazy as this.
>
> Tony




--

Tony Roberts
PP-ASEL
VFR OTT
Night
Almost Instrument :)
Cessna 172H C-GICE

[[email protected]]

On Mon, 02 Feb 2004 02:00:50 GMT, tony roberts >
wrote:

Cut- - -

>It kept working until I turned on the DME and then it lost satellite
>reception. The DME was tuned to 109.5 - I don't know what that is - it
>had been switched during the annual.
>I turned off the DME, rebooted the GPS and it worked fine. Turned the
>DME back on - the GPS lost reception. Then I turned the DME tuner up one
>to 110.5 anfd the GPS worked fine. I tried it on several other settings
>and it worked fine. Each time the DME was tuned back to 109.5 the GPS
>lost its satellites.
>Just thought I'd share that in case anyone has a GPS loss of reception
>in flight. It could just be something as crazy as this.
>
>Tony

We get 'No Fix Possible' when DME on 108.6 MHz with our Skyforce II.
The DME is a combined VOR/ILS/DME type Narco IDME 825.

Before replacing a faulty internal GPS antenna to an exteral antenna
the GPS was being blocked on more frequencies. In particular out local
VOR 109.2, but that's now ok with the external antenna.

Interestingly enough my handheld Flightmate Pro GPS ALWAYS works at
the same time using an antenna on the top of the instrument panel.




E-mail (Remove Space after pilot): pilot

[[email protected]]

On 1-Feb-2004, tony roberts > wrote:

> I now have the answer.
>
> Check out - http://www.scn.org/%7Ebk269/gps.html
>
> Tony


The cited article discusses interference from the local oscillators of VHF
nav and com receivers, not UHF DME systems. The interference mechanism from
DME is possibly quite different.

--
-Elliott Drucker