Originally Posted by KenR
...One thing that did happen yesterday has me a bit perplexed.
I have a Garmin 276c mounted on the bike. At two different times yesterday the GPS seemed to lose it's position, presumably after I hit the OK button of the Spot. The speed was still reading correctly in the display, but the map froze up and showed me about 300 miles from my correct position. Both times I simply rebooted the GPS and it went back to working correctly.
So I'm wondering if there's a conflict between the two devices or if this was just a coincidence. I've never had that happen with my 276 before yesterday....
I'm not surprised. The GPS satellites transmit in a band at 1,559 - 1,610 mHz and GPS receivers need to be quite sensitive as they usually don't have much antenna to work with. The GlobalStar/Spot systems' handset transmits in the band 1,610 - 1,625 mHz with significant power necessary to access a satellite in an orbit 1,000 miles up (again with little help from the antenna). This probably overloads the GPS' receiver. I doubt that these civilian units are designed to reject relatively huge signals on adjacent frequencies.
A cure? Dunno -- anything you can do to separate the GPS and Spot antennas as much as posible will help. Let us know if you have any luck with this.