Users manual
NR7000
Revision #:
B
Date:
102121
Page #:
13 of 24
www.novuspower.com
6.0 GNSS Function
The receiver needs to be able to see at least four satellite
vehicles (SVs) to obtain an accurate 3-D position fix. When
travelling in a valley or built-up area, or under heavy tree cover,
you will experience difficulty acquiring and maintaining a
coherent satellite lock. Complete satellite lock may be lost or
only enough satellites (3) tracked to be able to compute a 2-D
position fix, or a poor 3-D fix due to insufficient satellite
geometry (i.e. poor DOP). Inside a building or beneath a bridge,
it may not be possible to update a position fix. The receiver can
operate in 2-D mode if it goes down to seeing only three
satellites by assuming its height remains constant. But this
assumption can lead to very large errors, especially when a
change in height does occur. A 2-D position fix is not
considered a good or accurat
e fix; it is simply “better than
nothing”.
The receiver’s antenna must have a clear view of the sky to
acquire satellite lock. Remember, it is the location of the
antenna that will be given as the position fix. If the antenna is
mounted on a vehicle, survey pole or backpack, allowance for
this must be made when using the solution.
To measure the range from the satellite to the receiver, two
criteria are required: signal transmission time and signal
reception time. All GNSS satellites have several atomic clocks
that keep precise time and are used to time-tag the message
(i.e. code the transmission time onto the signal) and to control
the transmission sequence of the coded signal. The receiver
has an internal clock to precisely identify the arrival time of the
signal. Transit speed of the signal is a known constant (the
speed of light), therefore: time x speed of light = distance.
Once the receiver calculates the range to a satellite, it knows
that it lies somewhere on an imaginary sphere whose radius is
equal to this range. If a second satellite is then found, a second
sphere can again be calculated from this range information.
