5.1.3 Powering up a GNSS Receiver
If both the antenna and the power supply have been connected the system is ready to operate. Depending on
the type of oscillator installed in the receiver it takes about 10 seconds (OCXO-LQ) until 3 minutes (OCXO-MQ
/ HQ) until the oscillator has warmed up and reached the required frequency accuracy.
If the receiver has some valid almanac data in its battery buffered memory and the receiver’s position has
not changed significantly since its last operation the receiver can determine which satellites are in view. Only
a single satellite needs to be received to synchronize and generate output pulses, so synchronization can be
achieved at least one minute (OCXO-LQ) until 10 minutes (OCXO-MQ / HQ) after power-up. After 20 minutes
of operation the OCXO is fully adjusted and the generated frequencies are within the specified tolerances.
If the receiver position has changed by some hundred kilometers since last operation, the expected satel-
lites may not be in view after power-up. In this case the receiver switches to
Warm Boot
mode where it starts
scanning for all possible satellites one after the other. Once the receiver can track at least 4 satellites at the
same time it updates its own position and switches to
Normal Operation
.
If no valid data can be found in the battery buffered memory, e.g. because the battery has been discon-
nected or replaced, the receiver has to scan for satellites and collect the current almanac and ephemeris data
first. This mode is called
Cold Boot
, and it takes at least 12 minutes until all required data have been collected.
The reason is that the satellites send all data repeatedly once every 12 minutes. After data collection is com-
plete the receiver switches to
Warm Boot
mode to scan for more satellites, and finally enters
Normal Operation
.
In the default configuration neither pulse and synthesizer outputs, nor the serial ports are enabled after power-
up until synchronization has been achieved. However, it is possible to configure some or all of those outputs to
be enabled immediately after power-up.
If the system starts up in a new environment (e. g. receiver position has changed or new power supply
has been installed) it can take some minutes until the oscillator’s output frequency has been adjusted properly.
In this case the accuracy of the output frequency and pulses is also reduced until the receiver’s control loops
have settled again.
On the frontpanel ("Reference Time
→
Info GPS
→
GPS Satellites") as well as via the Web GUI ("Clock
→
Receiver Information") you can check the number of satellites that are in view (i.e. above the horizon) and
considered good (i.e. are healthy and can be tracked).
22
Date: 2nd July 2020
IMS - LANTIME M4000
