LTE-Lite GPSDO Evaluation Kit

© Brooke Clarke 2014

    GPS Antenna
    Synthesized PLL Clock Output
    What's in the Box  
    Manuals & Software Etc.
    Features & Limitations


Got this as part of my interest in GPS (Wiki) and GPSDOs (Wiki).



This is a new GPS Disiplined Oscillator (Wiki) with specifications that are higher than the surplus ones that are on eBay, yet is reasonably priced, i.e. a bargain.
It's made by Jackson Labs - LTE-Lite  The LTE-Lite is a small SMT module (1.18" x 0.7").  The LTE-Lite Eval kit mounts that module on a 2.95" x 1.788" Eval PCB.  The eval board has almost all the glue circuitry needed to use the LTE-Lite in a number of applications.  This evaluation kit is incomplete because how it's connected to the final application depends on what specifications are more important.

Note: The reference designations are different for the SMT module and for the Eval board, this can be confusing.  I'll use the Eval Board designations and will specifically state when I'm using the SMT module designations.

This unit can be used as the basis of an Open Traceable Time Platform - other options use: BeagleBone Black Single Board Computer, a Field Programmable Gate Array (FPGA), or the NVS NV08C GPS timing receiver.


The LTE-Lite SMT board has it's own TCXO which is the "internal" one and the Eval Board has the DIP-14 oscillator which is the "external" one.

The Eval board has a socket for a standard DIP-14 unit oscillator.  There is a large selection of oscillators in that form factor ranging for fixed frequency Plain Jane types to Temperature Compensated (TCXO) and even Oven-controlled (OCXO) (Wiki: osc abbreviations).  This particular version has a 10 MHz TCXO, but there are a number of frequency options.

Since this is a GPSDO the unit oscillator needs to have an Electronic Frequency Control (EFC) input.  That allows the oscillator to be part of a feedback loop (Wiki) that keeps the oscillator on frequency.  Prior to the GPSDO ordinary crystal oscillators needed to be "calibrated" every year or so.

The output from the CMOS DIP-14 oscillator is part of an analog feedback loop which includes the GPSDO module.  The GPSDO module has a CMOS (3.3V) digital output that's connected directly to J2 "20 MHz Out".  Note the actual output frequency on J2 depends on which DIP-14 oscillator is installed.  This is a high impedance CMOS square wave and so how it's buffered depends on how it's going to be used.  That circuitry will be different for frequency multiplication or for use to drive 50 Ohm coax as a frequency standard.

In order to get good Allan Deviation (Wiki) and Phase Noise (Wiki) performance analog control circuitry is used to drive the EFC input of the unit oscillator rather than using a Numerically Controlled Oscillator (Wiki NCO).  When working with 1 Pulse Per Second (PPS) signals the time domain (Wiki) measure Allan Deviation is used and when working with frequency multipliers the frequency domain (Wiki) measure of phase noise is commonly used, but they are really different ways of expressing the same thing and there's a way to convert from one to the other.

Using with lab grade oscillators:  In terms of external oscillators, you just need to feed your 10MHz or 20MHz INTO J2 (make sure to remove the DIP-14 TCXO from the board first!) and grab the 0V to 5V EFC from pin 1 of the DIP-14 socket. We tried that here with various DOCXO units (with CMOS output!) and it worked really well.


The GPS receiver is based on the SkyTraq - Venus838LPx GPS module.  The module is much more than just a GPS receiver.
Note that the GPS receiver has an internal oscillator and a provision to use an external oscillator.  The LTE-Lite Eval board has a switch to allow using either the oscillator in the GPS receiver (probably poor quality) or the external DEP-14 oscillator on the Eval board.

SkyTraq also make a GPS/GLONSS module that might be in a future eval kit?
Ans:  We evaluated a Glonass unit for 1PPS and it was really quite bad. Unless you are near the poles or get jammed a lot I would not see much advantage.

One of the output streams is NMEA 0183 (Wiki) data consisting of a number of different sentences.
The other option is a single propitiatory NMEA type sentence.
In both cases there is only NMEA output, there are no commands supported to the Eval Kit.

It is possible to use the ISP feature of the GPS module by means of the JP1 2x8 0.1" header, but that's not supported as part of the Eval Kit although it may be supported through SkyTraq.

GPS Antenna

The antenna connects to J4 "Ant In" which supplies 3.3 Volts at up to 60 ma for an active GPS antenna.  Note that different active GPS antennas are specified for a specific voltage usually in the range between 3.0 and 16.0 VDC and usually with positive on the center conductor.  But, most of them will work with almost any voltage in that range.  WARNING: if you use a GPS antenna at a voltage higher than that specified and burn it out it's your problem, not mine!  The military DAGR uses about 3 volts of antenna drive and here's some data on how a number of surplus antennas work there.

Synthesized PLL Clock Output

There is a built-in frequency synthesizer with three control bits, off and seven standard frequencies that depend on the frequency of the DIP-14 unit oscillator.
This output is direct from the GPSDO module to J5 "Clock Out" with a shunt diode.  This is a digitally synthesized frequency so will not have the good Allan Dev/Phase Noise that you get with the J2 output, but is useful as a clock for driving digital circuitry.

The frequency is set using up to three standard 0.1" jumpers on the top three rows of JP1.

10 MHz
15.36 MHz
MHz Out
19.2 MHz
20.0 MHz
Pin 11
Pin 10
Pin 9
- -
- - Jmp
- Jmp -
- Jmp Jmp
Jmp - -
Jmp - Jmp
Jmp Jmp -
Jmp Jmp Jmp

What's in the Box


Manuals, FAQ, Data Sheets &Etc on the Jackson Labs LTE-Lite web page.

GPSDO Control Program (ZX38xx) on the Jackson Labs support web page.

Features & Limitations

Good Allan Deviation and Phase Noise on the J2 output, but that requires adding appropriate interface circuitry.
Low price point for the performance.
Data Outputs: You can listen to PJLTS on the USB and grab the Skytrack NMEA in TTL format from pin 13 of header JP1 at the same time..


Fig 1 Eval Kit fits small USPS Priority box
                    GPSDO Evaluation Kit
Fig 2 Eval board top
                    GPSDO Evaluation Kit
Fig 3 Eval board bottom
                    GPSDO Evaluation Kit


Alphanumeric web page index (all my web pages)
Disciplined  Oscillator Patents
HP E1938 Ovenized Crystal Oscillator
HP Z3805A Time & Frequency GPS Receiver GPSDO
Trimble ThunderBolt Timing GPS Receiver GPSDO
CSI LGBX Pro DGPS Receiver
FEI Frequency Standards
GPS antennas at DAGR and Trimpack
Lucent KS-24361 HP/Symmetricom Z3809A, Z3810A, Z3811A, Z3812A GPSDO System
PSN-8 VSN-8 GPS receiver
PSN-9 GPS receiver
PSN-10 SLGR GPS receiver (Trimpack)
PSN-11 PLGR GPS receiver
PSN-13 DAGR GPS receiver
PLGR GPS receivers
PLGR-II Rockwell HNV-2000 PLGR II SPGR GPS Receiver
DAGR GPS receivers
HNV-600 Rockwell Trooper
HNV-2000 Rockwell PLGR II SPGR GPS Receiver
Magellan GPS Commander
Magnavox MX7221 GPS Receiver
Trimpack & other Trimble GPS receivers
Thunderbolt Trimble timing GPSDO receiver
Ashtech Z12 GPS Carrier Phase Receiver
Stanford Telecom 5001A Single Satellite GPS Signal Generator
Northern Telecon GPS Satellite Simulator STR2760
Precision GPS Measurements From: "Dr Thomas A Clark (W3IWI)"
4-Way GPS Signal Splitter using Cable TV Parts
GPS & Satellite Navigation Patents
Motorola GPS Receivers
MX 4102 Transit Satellite Navigator & MX 4200 Differential GPS receiver
Quantic Q-5200/SM Timing GPS Receiver with crypto key input
URN-502 Vehicle Mount First Generation (huge) GPS Receiver System


eBay Ad LTE-Lite GPSDO Evaluation Kit with 10MHz TCXO - Jackson Labs eBay

Tindie -
Venus838FLPx GPS Breakout Board -
Venus838FLPx GPS Breakout Datasheet
Venus838FLPx Breakout Schematic
Venus838FLPx Breakout Gerbers
Venus838FLPx Datasheet v4
Application Note AN0026, 4-Hour ROM AGPS Extension, For Venus6、Venus 8 GPS Receiver Ver 0.3, February 19, 2014
Satellite Viewer Software
USB Drivers
Firmware 2014-04-16

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page page created 25 Nov 2014.