AirTalk.org Aviation discussions newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  GPS WEIRDNESS          AirTalk.org Forum Index -> Instrument Flight Rules View previous topic :: View next topic   Author Message Guest Posted: Wed Feb 23, 2005 6:59 pm    Post subject: GPS WEIRDNESS Flew my 172M today and experienced some truly bizarre GPS behavior. On preflight my portable GPS (Garmin 296), with external antenna and aircraft power securely attached, initialized just fine, acquired several satellites and went right into NAV mode. After runup and right before takeoff, it showed total loss of satellite signals and even after cycling power several times, would not pick them up again. With the utmost confidence in my pilotage skills (sarcasm intended) I took off and hoped to see valid GPS signals in flight. No dice. we fired up the copilot's Garmin 195 portable, and with a fresh load of batteries and the external antenna connected tried to pick up a signal. Once again, nothing. This persisted on both portable units for a good 10 minutes, including a climb up to 4500' MSL. I tried individually cycling power on the vast avionics array (dual ancient NARCOs, King DME, pre-Cambrian ADF and King XPNDR) and lo and behold, when the transponder was turned off and then back on, both portable GPS units came to life, acquired multiple satellites and worked perfectly. Looking back, the 296 probably pooped out when the transponder went on in the runup area. On the trip back, there was no problem on either portable unit when the transponder was turned on. Has anybody ever seen the 296 (or their own portable) act like this?? Back to top Dan Luke Guest Posted: Wed Feb 23, 2005 7:34 pm    Post subject: Re: GPS WEIRDNESS <nospam (AT) ih (DOT) com> wrote: Quote: Looking back, the 296 probably pooped out when the transponder went on in the runup area. On the trip back, there was no problem on either portable unit when the transponder was turned on. Has anybody ever seen the 296 (or their own portable) act like this?? On a couple of occasions I've had a Garmin portable (a GPS III Pilot first, later a 296) "flatline" due to interference from a Cessna NAV-Com, but only during transmission. Both times I swapped out the radio and that fixed the problem. -- Dan C-172RG at BFM Back to top Dave Butler Guest Posted: Wed Feb 23, 2005 8:00 pm    Post subject: Re: GPS WEIRDNESS Quote: nospam (AT) ih (DOT) com> wrote: Has anybody ever seen the 296 (or their own portable) act like this?? My Garmin 196, and before it, my Garmin 90 would both crap out when the NAV radio was tuned to a certain VOR frequency. Back to top aluckyguess Guest Posted: Tue Mar 01, 2005 4:42 am    Post subject: Re: GPS WEIRDNESS My 296 did that the other day also. It was only finding 2 sats. It did this of and on the whole trip. I have never even and a blip with this unit before. <nospam (AT) ih (DOT) com> wrote Quote: Flew my 172M today and experienced some truly bizarre GPS behavior. On preflight my portable GPS (Garmin 296), with external antenna and aircraft power securely attached, initialized just fine, acquired several satellites and went right into NAV mode. After runup and right before takeoff, it showed total loss of satellite signals and even after cycling power several times, would not pick them up again. With the utmost confidence in my pilotage skills (sarcasm intended) I took off and hoped to see valid GPS signals in flight. No dice. we fired up the copilot's Garmin 195 portable, and with a fresh load of batteries and the external antenna connected tried to pick up a signal. Once again, nothing. This persisted on both portable units for a good 10 minutes, including a climb up to 4500' MSL. I tried individually cycling power on the vast avionics array (dual ancient NARCOs, King DME, pre-Cambrian ADF and King XPNDR) and lo and behold, when the transponder was turned off and then back on, both portable GPS units came to life, acquired multiple satellites and worked perfectly. Looking back, the 296 probably pooped out when the transponder went on in the runup area. On the trip back, there was no problem on either portable unit when the transponder was turned on. Has anybody ever seen the 296 (or their own portable) act like this?? Back to top L. R. Du Broff Guest Posted: Thu Mar 17, 2005 1:37 am    Post subject: Re: GPS WEIRDNESS I had a Garmin 95 XL that lost signal every time the VOR was tuned to 108.8. Finally figured out that it was the associated DME channel. ie, when my DME transmitted, a harmonic wiped out GPS reception. Another wierd one: Apollo (ii Morrow) UPSAT GarminAT (they keep changing names) GX-60, IFR installation. Whenever I started up on the north ramp at SFB (Orlando-Sanford), the GPS would not initialize. I had to wait until airborn, turn it off and back on again, and no problem. Starting up anywhere else on that airport, or at any other airport, no problem. The dealer at the north ramp of SFB could never figure the problem. I finally cured the problem when I stopped using that FBO (for other reasons). "" <nospam (AT) ih (DOT) com> wrote in news:FKCdnZHrBfcUT4HfRVn-vA (AT) comcast (DOT) com: Quote: Flew my 172M today and experienced some truly bizarre GPS behavior. On preflight my portable GPS (Garmin 296), with external antenna and aircraft power securely attached, initialized just fine, acquired several satellites and went right into NAV mode. After runup and right before takeoff, it showed total loss of satellite signals and even after cycling power several times, would not pick them up again. Back to top Dave Butler Guest Posted: Fri Mar 18, 2005 6:33 pm    Post subject: Re: GPS WEIRDNESS L. R. Du Broff wrote: Quote: I had a Garmin 95 XL that lost signal every time the VOR was tuned to 108.8. Finally figured out that it was the associated DME channel. ie, when my DME transmitted, a harmonic wiped out GPS reception. 108.8 is/was also one of the freqs that would cause my old Garmin 90 and current Garmin 196 to lose reception. 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