4 GNSS Receiver
4.1.3.2 Menu Option Setup MRS
The internal reference clock of the integrated clock module with the high precision oscillator (OCXO HQ) can
be disciplined by different time sources. Possible time sources are GPS receiver, external Pulse Per Second
(PPS), IRIG 10MHz Frequency, IRIG Time Code, external NTP server or IEEE1588 Grandmaster (M400, M600,
M900). The priorities for the internal controlling can be set up in configuration. The priority will define which
reference source will be used next if the highest priority reference source will be no longer available. For each
reference source a bias (fixed offset) and a precision value can be defined.
MRS
>Set MRS & Info<
IRIG Receiver
> MRS Status <
Priorities
Fix Offsets
Precisions
0.GPS* +32.0ns
1.NTP +6.000us
2.PPS n/a
3.PTP n/a
MRS Status
> Priorities <
Fix Offsets
Precisions
0. GPS
1. PPS in
2. NTP
3. PTP IEEE1588
MRS Status
Priorities
> Fix Offsets <
Precisions
Set FixOff[ns]
PPS:
NTP:
PTP:
MRS Status
Priorities
Fix Offsets
> Precisions <
Set Precis[ns]
GPS:10
PPS:100
NTP:
OK
OK
OK
OK
OK
With the OK and arrow buttons you can choose the current status of the MRS. All possible reference clocks
will be shown with the number of priority, the name of the reference clock and the current offset to the inter-
nal reference clock (OCXO). The current master will be signed with an “*” behind the name of the reference clock.
In the next menu the user can define in which order the references will be used to control the internal os-
cillator. The reference clock with the highest priority will be used always if this is available.
The "Fixed Offsets" can be set up in the next sub menu, if you know the constant offset (bias) of an exter-
nal reference source. By default this value is 0 ns. The bias of the internal GPS receiver can not be set up –
indirectly this can be done via the antenna cable length.
This precision value will determine the hold over time when switching to the next reference clock if the current
master is not available anymore. If the precision is 0 the next reference clock will be switched at once. If the
precision value is greater then 0 the time for switching to the next reference (hold over time) will be calculated
by the following formula:
(precision of next reference) / (precision of current master) * constant [s]
The parameter „constant“ depends on the quality of the internal oscillator.
IMS-GNS181 Setup Guide
Date: 20th March 2020
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