SXBlue GPS Reference Manual
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broadcast ionospheric model until it has downloaded the SBAS map, which can result in
lower performance as compared to when the map has been downloaded. This will be the
case for any GPS product supporting SBAS services.
Caution – When the map has been downloaded, you may observe a position jump due
to the potential difference between the GPS ionospheric model and the ionospheric
SBAS map. To minimize the impact of this issue on your use of the SXBlue GPS, you
may wish to wait up to five minutes before using the SXBlue GPS or issue the
$JQUERY,GUIDE<CR><LF> message to ‘ask’ the SXBlue GPS if it feels performance
will be sufficient for operation.
2.3 COAST™ Technology
The SXBlue GPS receiver incorporates the COAST
TM
technology that allows it to operate
with old correction data for up to 30 to 40 minutes or more without significant accuracy
degradation. The feature’s performance is attributed to sophisticated algorithms that are
able to anticipate how errors change during a period of correction loss.
Traditional receiver technology would experience an increasing degradation with increasing
age of corrections, resulting in less than adequate performance over a shorter period of
time. COAST technology provides more consistent positioning during periods when signal
loss occurs, thus bridging the gap to when the signal is reacquired. This means that the
SXBlue GPS is more tolerant than competing products to loss of SBAS or externally input
RTCM SC-104 corrections.
2.4 e-Dif – Extended Differential Option
The SXBlue GPS receiver is designed to operate with the optional e-Dif software. e-Dif is a
mode where the SXBlue GPS can perform with differential-like accuracy for extended
periods without the use of a differential service. It models the effects of ionosphere,
troposphere, and timing errors for extended periods by computing its own set of pseudo-
corrections.
e-Dif may be used anywhere geographically and is especially useful where SBAS networks
have not yet been installed, such as South America, Africa, Australia, and Asia. Since e-Dif
is an option, it will either come pre-installed inside your SXBlue GPS, or you may order the
option at a later time. It can be easily installed in the field using a PC computer and some
simple software if not pre-installed.
Positioning with e-Dif is relatively jump-free, provided that the SXBlue GPS maintains lock
on at least four satellites at one time. The accuracy of positioning will have a slow drift that
limits the use of e-Dif for approximately 30 to 40 minutes, however, it depends on how
tolerable your application is to drift, as e-Dif can be used for longer periods.
You should test this mode of operation and determine if it’s suitable for your application and
for how long you’re comfortable with its use. As accuracy will slowly drift, you need to
determine at what point you would like to recalibrate e-Dif in order to maintain a certain level
of accuracy.
