Low Noise Rubidium GNSDO RELEASE NOTES Rev. 1.0
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1. Jackson Labs J ackson Labs Technologies Inc 1635 Village Ctr Cir Suite 150 Las Vegas NV 89134 Phone 1 702 233 1334 support jackson labs com DATE AUGUST 18 2015 Low Noise Rubidium GNSDO RELEASE NOTES Rev 1 0 Document Number 80200527 ITEM 1 Automatic Initialization of Position Hold Auto Survey Mode N B The LN Rb GNSDO supports automatic Position Survey and Position Hold mode for the GNSS receiver Position Hold mode requires the GPS Glonass antenna to be stationary The unit will not work properly if the GNSS antenna is moved while Position Hold mode is enabled This stationary mode is enabled by default when the unit is shipped from the factory as the GNSS is able to provide better timing stability and operation with only a single Satellite in Position Hold mode Solution If the GNSS 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 it is stored in EEPROM GPS TMODE OFF The unit can then be set to Automatic Dynamic mode which will adjust the GPS Kalman filter parameters based on vehicle velocity To enable Automatic Dynamic mode send the following command GPS DYNAMIC MODE 8 Automatic Dynamic mode is explained in detail in section 3 3 14 in the LN Rb GNSDO user manual To re enable Auto Survey mode after power on send the following command GPS TMODE RSTSURV This is described in furt2. e without excessive ringing or over undershoot The principle of series terminating coax cables transmission lines or micro strip lines driven by CMOS outputs 1s explained in detail in the literature see for example the PCI bus system Specification info jackson labs com Copyright 2012 2015 Jackson Labs All rights reserved Last updated 08 18 15
3. her detail in section 3 3 19 in the LN Rb GNSDO user manual info jackson labs com Copyright 2012 2015 Jackson Labs All rights reserved Last updated 08 18 15 ITEM 2 Driving 50 Ohms coax cables with the 1PPS and 5MHz CMOS outputs N B The 5V CMOS IPPS and 5MHz outputs of the LN Rb GNSDO are designed to drive open ended 50 Ohms coax cables The drivers can supply up to 15mA of output current These outputs should not be terminated by 50 Ohms terminations as this would cause short circuiting inside the output driver Driving 5V into 50 Ohms requires a minimum current of 0 1A which these drivers are not capable nor designed to drive Solution To reduce power consumption to a minimum CMOS outputs such as the IPPS and 5MHz outputs on the LN Rb GNSDO are designed to drive 50 Ohm 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 50 Ohms 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 IK Ohms or higher end terminations Signals will travel down the coax cable be reflected 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 edg
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