Everything I know about GPS

When Streets and Trips came out with a bundled GPS receiver I picked one up, ordered a CF Sled so I could use it with my antique Pocket PC and had a whirl. It was fun for a while but then we got a Prius with GPS in the dash, and S&T doesn't have maps of fun places like New Zealand so I haven't used it often. I do want to share one thing I learned when I was first trying it out and shared with co-workers who were having similar issues.


Are you waiting long enough?

I received enlightening information on another e-mail list that it can take up to 5 minutes to get a signal. Roughly, the GPS satellites radiate big data chunks on a less frequent basis and smaller, incremental data chunks more frequently. The GPS receiver must wait until it sees a big data chunk from several satellites before it can do anything. This is called “time to first fix” (TTFF), and can take 2-5 minutes even in completely optimal conditions.

With my Dell Axim and the Pharos GPS receiver (using a CF adapter) I have to wait about 2-3 minutes after plugging it in before I get a fix. After that, everything is groovy. No drivers needed. (In my first attempts I was assuming the satellites were radiating data constantly so I only gave it ~30 seconds before giving up and yanking the card, restarting, etc.)


I picked up a shiny Verizon VX6700 (a.k.a. HTC Apache) which has Bluetooth and EVDO so I might pick up a Bluetooth GPS adapter, just so I can play with Virtual Earth Mobile.