What makes my New GPS so much better then my old one?

I started using a Toshiba e740 PDA with a Globalsat BC307 about 2 years
ago. And in the car used it with an antenna extension and it works fine
with this. But takes a few minutes to find a lock (in London area)

More recently I got a Viewsonic V37 and bought a Hi-Com 204E GPS to use
with it and bascally I've been blown away by how much more easily I
pick up a signal with the newer GPS unit. For instance I can get a
signal lock from inside side of my bedroom window, whereas with the
BC307 even if I put the whole PDA onthe window ledge I won't get a
lock. Also inthe car it locks on within a few seconds compared to my
BC307 which can take several minutes to find a lock using and external
antenna.

I want to buy a new Compact Flash GPS for my Toshiba PDA to use when
travelling and walking in European Cities - what should I be looking
for?

I find with the BC307 it's really hard to get an inital lock on a
signal, for instance I was in very open ground in Stockholm recently
and stood outside for more then 20 minutes struggling to get a lock.

Then today I had my Toshiba in a big Van with just the Compact Flash
GPS and no extension Antenna and again took ages to get a lock and then
later in the journey it lost the lock and I just couldn't get it back.
However my friend had a Tom Tom 700 unit in the Van and that was
getting an excellent signal at all times, even when I had the unit on
my lap away from the windscreen, but my 307 right on the front
windscreen was struggling through the entire journey.

I live in London and want to travel more in European cities, so what is
the features I want to look out for in buying a new GPS?

What is it about the 307 unit that make it such a poor performer
compared to the other units I mentioned?

I've seen a haicom Hi-303III will that work much better then a BC307?

What is the benefits of Sirf 3/ III or Xtrac?

Many thanks for all help

At the moment you bascially need to look at any unit with a SRIF III
chipset. I've no idea on the technical details of why it's better, I guess
it must be just better signal processing firmware which can do something
with a low signal level that the older receivers could not.

I blieve Xtrac is one of the components of older systems and isn't in SRIF
III so you probably want to avoid those.

charlie wrote:

I sure hope you don't mean "locks on within fewer than 30 seconds",
because if you do, the GPSR's algorithm is not ensuring you have
proper ephemeris data.

Sam Wormley wrote:


I haven't broken down and bought any GPS yet.

But, I gotten the impression that if a GPS:
1. is operating.
2. is powered down.
3. power is reapplied some time later at the same location, lock will be
achieved much sooner than if power reapplied at some distant location.

Could it be newer unit is better at retaining data and thus tends more
often to "start" in "warm start"?

Richard Owlett wrote:

Suggest reading: http://www.navcen.uscg.gov/pubs/gps/gpsuser/gpsuser.pdf