Archives for 2006

NOTE: A much more current version of this post can be found here.

A GPS receiver discerns your position on the surface of the earth by measuring the length of time it takes to receive signals from satellites. It cannot, however, tell what direction you are facing while standing still (or moving slowly). So if you are navigating to a waypoint, a basic GPS can only point you in the correct direction once you are moving.

This is where an electronic compass comes in handy. It can tell what direction you are facing, even while standing still. Not only does this make navigating easier, it also helps with projecting waypoints and orienting paper maps. Units with an electronic compass usually have a barometric altimeter as well.

Some of the latest models even have a tri-axial compass, meaning you don’t even have to hold it level.

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UPDATE: Here’s my 2010 take on SiRFstar III, which is rarely available these days.

There are a lot of hot new GPS receivers that use the SiRFstar III chipset, but unless you’re a heavy-duty GPS aficionado, you may be wondering, what the heck is this thing and what is the big deal? Simply put, it is a GPS receiver chipset. This is the little piece of silicon responsible for receiving GPS signals and passing the coordinate information along to a miniature computer in your GPS unit.

Why is it a big deal? Fast acquisition times and processing power. This translates into less likelihood of lost signals under canopy and in urban (or natural) canyons. In canyon-like environments, your GPS receives signals directly from satellites whenever it can, but it also receives reflected signals, bouncing off hard surfaces (multipath reflection). Your GPS determines your
position by calculating how long it takes the satellite signal to reach your receiver, so reflected signals are a source of error. The SiRFstar III chipset has the processing power to do a lot of "what if’s" with these reflected signals. This processing power also means that the chipset can consider weak signals that were ignored by previous chipsets. The SiRFstar III also has faster acquisition times, making for a faster time to first fix (TTFF), and a quicker reacquisition if the signal is lost.

All of this translates into amazing reception, under canopy, in urban centers and even indoors. And that is why the new Garmin units with this chipset are so hot.

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