SiRF III: is sensitivity better than accuracy?

I recently bought a Holux 240 largely because it contained the SiRF
III chipset with high sensitivity and low power consumption. I have
been trying for a week to find out how to enable WAAS support in this
device. Turns out that SiRF does not claim it *has* WAAS support!
Basically SiRF said that the OEMs (Holux) can modify the design to
suit themselves and can disable features such as WAAS.

I have not been able to get Holux to respond to requests for support
and their web site provides nothing useful in trying to use any WAAS
capabilities this unit may have. Holux provides a program called GPS
Viewer which sends a "$PSRF108,01" command when WAAS is selected in
the user interface. But this command seems to be ignored by the
device and no indication shows that WAAS capability has been
enabled.

I have been searching for a several days for information on how to use
WAAS on SiRF III based receivers and it seems there is nothing
consistent that works with any number of units. I found one post on
gpspassion that said he got a GlobalSat SiRF III unit to work, but no
details and no one else confirmed it.

It would appear that since SiRF has no control over how the OEMs
implement their receivers, there is a lot of variation in the end
products using this technology. What everyone seems to tout about the
SiRF III units is their good sensitivity. But if they don't support
WAAS, the accuracy will not be good. So which is better, sensitivity
or accuracy?

I think that bad sensitivity automatically results in bad accuracy in most
cases.

--
Andreas van Hooijdonk
http://www.gps-practice-and-fun.com

There are different versions of firmware for the Sirf III. Supposedly,
the early versions did not support WAAS, but the more recent versions
do. You may have to enable WAAS with the SirfDemo program. At any
rate, you can use SirfDemo to read your firmware number and ask Sirf
if that version supports WAAS. Remember earlier caveats and don't
issue Sirf commands to change the baud rate.

Sirf has to respect non-disclosure agreements, so they won't answer
questions if you mention the name "Holux". With my Holux 236, the
Sirf chip is "stock", and it is probably the same for the 240. Other
than setting the default configuration, Holux has no reason to use
custom firmware.

Just a double check. Are you in a location where you can track the
WAAS satellites?

I have a Holux 213 (cheapest I could find on eBay :-), and WAAS
works as advertised. I routinely see PRN 48 (Galaxy 15) and
PRN 51 (Anik F1R) in the output data.

As far as I can tell from the SiRF documentation, the device
is a totally standard SiRF III.

Laura Halliday VE7LDH "Que les nuages soient notre
Grid: CN89mg pied a terre..."
ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte

Yes, but that is a very different animal from the bluetooth
receivers. The bluetooth receivers have an extra chip to handle the
bluetooth functions and acts as a middleman in all communications.
For whatever reason, the idividual vendors seem to modify the code on
the SiRF chip to add commands I would expect. But I doubt that Holux
has done this since they don't bother to provide any documentation.
What good would additional commands be without docs?

I think Holux is simply too lazy to care if their users can use WAAS
and don't bother to add any NMEA commands to enable it. I expect SiRF
binary commands will work, but I have not been able to get it working
so far. Again, it's not like I am going to get any support from
Holux!

The only question left in my mind is just how much of an improvement
you will get from having WAAS enabled and working. The people from
SiRF seem to be saying it will only improved accuracy by 1 to 2
meters. But they only support that statement under perfect conditions
and then try to extrapolate to the real world. If I ever get WAAS to
work on this unit, I will do some real world testing.