+RoyalRed Posted March 31, 2004 Share Posted March 31, 2004 (edited) I have been Geocaching a little over one month and have logged 50 finds so far. I was quite amazed at GPS performance under power lines. Last weekend we were searching for a cache located directly underneath the approach for Philly airport. Seemed like every time a plane came ovehead the GPS would go crazy. Has anyone else seen this or am I the crazy one? Edited March 31, 2004 by RoyalRed Quote Link to comment
+IVxIV Posted March 31, 2004 Share Posted March 31, 2004 Well I haven't had that experience but,, I have used my GPSr while INSIDE a plane in flight (get a window seat & be patient for a lock lol) and it worked fine Quote Link to comment
+NightPilot Posted March 31, 2004 Share Posted March 31, 2004 I don't think the plane will be overhead long enough to affect GPS reception. It will only be between you and a satellite for an instant. You're likely seeing something else. Quote Link to comment
+GEO*Trailblazer 1 Posted March 31, 2004 Share Posted March 31, 2004 Yea I had it happen. Where are you looking.??????????.......They got your #you know!!! Quote Link to comment
+Wacka Posted March 31, 2004 Share Posted March 31, 2004 I had one case wher the GPr was pointing about 40 ft away from where the cache was . A plane was on its approach overhead (about 3-4000 ft up) and the GPSr switched to saying the cache was 10 ft away, which was where it was. Quote Link to comment
+Criminal Posted March 31, 2004 Share Posted March 31, 2004 I wonder if the plane's radar altimeter, which is shooting a signal straight at the ground, may be causing interference. I don't know the frequency of radar altimeters and if it or an image may be doing this. It is certainly feasible though. Quote Link to comment
+tirediron Posted March 31, 2004 Share Posted March 31, 2004 Depending on the application, RADALTs can operate at frequencies between 500 MHz and 9.8Ghz. While the signal could easily mess with your GPSr's mind, these use very narrow beamwidths, so any interference would be short lived. There are also a number of other emitters on any large aircraft, including IFF, Wx radar and approach radar which could contribute as well. Don't forget that any large airport is a virtual zoo of emissions over a huge part of the RF spectrum, so whether there is an actual plane overhead or not, reception could easily be "interesting" anywhere in that general area! Quote Link to comment
+Criminal Posted March 31, 2004 Share Posted March 31, 2004 Depending on the application, RADALTs can operate at frequencies between 500 MHz and 9.8Ghz. While the signal could easily mess with your GPSr's mind, these use very narrow beamwidths, so any interference would be short lived. There are also a number of other emitters on any large aircraft, including IFF, Wx radar and approach radar which could contribute as well. Don't forget that any large airport is a virtual zoo of emissions over a huge part of the RF spectrum, so whether there is an actual plane overhead or not, reception could easily be "interesting" anywhere in that general area! Yes, but the description made it appear that this was a short lived interference. Radar Alt is also the only beam directed (almost) straight down. Quote Link to comment
+tirediron Posted March 31, 2004 Share Posted March 31, 2004 Depending on the application, RADALTs can operate at frequencies between 500 MHz and 9.8Ghz. While the signal could easily mess with your GPSr's mind, these use very narrow beamwidths, so any interference would be short lived. There are also a number of other emitters on any large aircraft, including IFF, Wx radar and approach radar which could contribute as well. Don't forget that any large airport is a virtual zoo of emissions over a huge part of the RF spectrum, so whether there is an actual plane overhead or not, reception could easily be "interesting" anywhere in that general area! Yes, but the description made it appear that this was a short lived interference. Radar Alt is also the only beam directed (almost) straight down. Well.... a RADALT is probably the most downward looking emitter, but don't forget that a lot of large airliners use a CCA (Close-control Approach) system which is transmitted from a chin-dome and tends to be pushed downward as well. I agree that RADALT is the most likely candidate, but I think the short asnwer is: GPSr + Airport = Quote Link to comment
+NightPilot Posted April 1, 2004 Share Posted April 1, 2004 The weather radar, especially in ground-mapping mode, shoots pretty far down also. Close to an airport, I would tend to suspect the ATC radar, or maybe the Doppler weather/windshear radar, since they will be transmitting with much higher power than an aircraft does. More likely, just another anomaly received all the time on any GPSr. Coincidences happen all the time. An airplane flying overhead, especially one going as fast as an airliner, just won't be overhead long enough to do much to the GPS signals, either by blocking or interference via some transmitter. I could hover my helicopter over you and wouldn't block your GPS. Our GPS antennas receive through the rotor blades with no problem at all, and they're always turning above us. Quote Link to comment
+RoyalRed Posted April 2, 2004 Author Share Posted April 2, 2004 Thanks for all of your inputs. Will keep on caching as best as I can! Quote Link to comment
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.