Rohde & Schwarz CMU-K20, Operating Manual

Page: 161 / 646

CMU-K20/K21/K22/K23/K24 Non Signalling: Connection Control
1115.6088.12 4.83 E-11
The associated field allows to select between two alternatives:
Int. (10 MHz) Internal synchronization by means of a 10 MHz reference
frequency (TCXO or OCXO, CMU-B11/-B12).
Ext. (at REF IN) Synchronization to external reference signal to be fed in via input
REF IN. The external reference signal can be used for synchronization of the CMU
to another instrument. Its frequency must be entered in the input field next to the
External button.
The frequency of the external reference signal must be entered in the input field
next to the left of the
Ext. (at REF IN) radio button.
The reference signal used is also routed to output REF OUT 1 so that it can be fed
to other instruments as well.
Note:
1. The header cyclically displays a warning if no synchronization could be
achieved e.g. because of missing or faulty input signal with external
synchronization selected. At the same time, bit no. 6 (RFNL, Reference
Frequency Not Locked) is set in the STATus:OPERation:CMU:SUM1:CMU1
sub-register associated to the CMU base system and the query
[SENSe:]SYNChronize :FREQuency:REFerence:LOCKed?
returns the
value
ON
.
2. In the case of external synchronization with squarewave signals (TTL) ensure
correct signal matching to avoid reflections. Otherwise, resulting overshoots
may cause trigger problems at the CMU input. A possible remedy is to use a
lowpass filter or an attenuator pad directly at the CMU input. Correct
synchronization may be checked by comparing the signal REF OUT 1 or REF
OUT 2 with the input signal.
3. This configuration is valid in all CMU function groups.
Caution: The reference frequency is set to Int. (10 MHz) whenever the base
system is reset. After switching back to Ext. (at REF IN) it is necessary to allow for
a setting time (~1 s) before the CMU can synchronize to the external reference
frequency. The delay is avoided by a partial reset of all function groups with the
exception of the base system.
Remote control
The commands for the reference frequency are part of the CMU base system (see
CMU200/300 operating manual):
CONFigure:SYNChronize:FREQuency:REFerence:MODE
INTernal | EXTernal
CONFigure:SYNChronize:FREQuency:REFerence <Frequency>
[SENSe:]SYNChronize:FREQuency:REFerence:LOCKed?
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