CSAC Release Notes 1.2 - Jackson Labs Technologies, Inc.
Contents
1. Jackson Labs J ackson Labs Technologies Inc 475 Alberto Way Suite 120 Los Gatos CA 95032 Phone 1 408 354 7888 support jackson labs com DATE J ANUARY 30 2012 CSAC GPSDO RELEASE NOTES Rev 1 2 Document Number 80200505 ITEM 1 Automatic Initialization of Position Hold Auto Survey Mode Issue The CSAC GPSDO supports automatic Position Survey and Position Hold mode for the GPS Position Hold mode requires the GPS antenna to be stationary The unit will not work properly if the GPS antenna is moved while Position Hold mode is enabled This mode is enabled by default when the unit is shipped from the factory as the GPS 1s able to provide better timing stability and operation with only a single Satellite in Position Hold mode Solution If the GPS antenna is to be moved in a mobile application the user needs to disable Position Hold mode with the following SCPI command this command only needs to be issued once GPS TMODE OFF The unit can then be set to Automatic Dynamic mode which will adjust the GPS Kalmann filter parameters based on vehicle velocity To enable Automatic Dynamic mode send the following command GPS DYNAMIC MODE 8 Please note that the syntax for this command has change slightly in revision 0 48 and later firmware releases Automatic Dynamic mode is explained in detail in section 3 3 11 in the CSAC GPSDO user manual To re enable Auto Survey mode after power on send the following command GP2. S TMODE RSTSURV This is described in further detail in section 3 3 17 in the CSAC GPSDO user manual info jackson labs com Copyright 2012 Jackson Labs All rights reserved Last updated 01 30 12 ITEM 2 1PPS output leakage into 1OMHz signals Issue the 1PPS output signal can leak into the 1 OMHz output signals if the CSAC GPSDO 1PPS output is not properly connected to external equipment The CSAC GPSDO uses a common 5V power supply rail for the 1PPS output driver chip as well as the 1OMHz output driver chips Connecting a 50 Ohm end terminated cable to the 1PPS output connector will cause a current surge with up to 50mA to flow out of the 1PPS connector and this can cause IPPS signal leakage into the 1OMHz outputs through power supply voltage modulation creating higher phase noise at 10Hz to 100Hz offsets and potential phase instability in the LOMHz signal Solution To reduce power consumption to a minimum CMOS outputs such as the IPPS and 5MHz outputs on the CSAC GPSDO are designed to drive 5 00hm open ended coax or PCB transmission lines without resistive end termination CMOS outputs are not designed to drive 50 Ohm resistive terminated inputs and connecting a 50Ohms resistive termination will cause a DC short circuit current to flow in the output driver chip CMOS outputs are designed to drive 50 Ohm transmission lines and coax cables with IM Ohms or higher end terminations Signals will travel down the coax cable be re
3. flected by the open ended cable and then return to the CSAC GPSDO where they are properly terminated by a 50 Ohms series termination and thus the receiver connected to the coax cable will see a very well shaped rising or falling edge without excessive ringing or over undershoot The principle of series terminating coax cables transmission lines or micro strip lines driven by CMOS outputs is explained in detail in the literature see for example the PCI bus system specification info jackson labs com Copyright 2012 Jackson Labs All rights reserved Last updated 01 30 12
Download Pdf Manuals
Related Search