GPS PC-board 6038
hopf
hopf
Elektronik
version 03.01
page 13
Width of the DCF77-Simulation pulses
The transmitter DCF77 broadcasts a data string, which transmits the time information with one
bit per second. The lowering of the amplitude for 100 or 200 msec codes the digital information
(0/1).
Due to the narrow band nature of their antennas, some strange makes of radio controlled clocks
distort the duration of the lowering, so that the respective receiver connected on load side must
be set to a different pulse length. The value for the high pulse can be adjusted in the range of
140-230 msec and the low-pulse in the range of 50-130 msec so that those receivers can run
safely with the DCF77-simulation.
4.2.6 Time Decoding 3D / Position fix
The accuracy of the time evaluation depends on how accurately the position of the operational
location is calculated. At least the reception of 4 satellites is necessary in the 3D evaluation
mode. From the calculated position the transit time of the signal to several satellites is found and
the second marker is produced from the average transit times. The
3D
evaluation mode allows
the second marker to have an accuracy of ± 1
µ
sec.
In case of a fixed position quite often a less substantial evaluation of the second marker suffices
e.g. up to some milliseconds. In the position-fix mode the accuracy depends mainly on the pre-
cise entry of the position of the location of the installation. The calculation of the second marker
starts with one satellite and the entered position already. An entry of the position to ± 1 minute
degree achieves an accuracy of the second marker better than ± 20
µ
sec. An entry even more
precise can achieve the value ± 1
µ
sec.
The position-fix mode has the advantage that the clock synchronises with only one received sat-
ellite. The antenna may be installed somewhere where less than ¼ of the sky is visible.
Often it is possible to install the antenna indoors at the window (short cable, no lightning protec-
tion). If 4 received satellites are visible in this mode, the evaluation jumps automatically into the
3D mode and calculates the exact position improving the accuracy to ± 5
µ
sec for one satellite.
The following entry sequence set the modes
selection picture
Set mode of the GPS Evaluation
1 = 3 D Evaluation
2 = Position Fixed
MODE (1-2) =
Entering
"1"
or
"2"
switches the evaluation to the according mode. The entry can be checked in
the main menu under pt. 8. The line
Mode of GPS Evaluation:
shows the set mode:
3-D Evaluation
Position Fixed
