Novus NR300 User manual

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NR300
Portable Battery Powered Rubidium Reference
All information provided herein is the property of Novus Power Products
LLC. The information included may be reproduced without the permission of Novus
Power Products LLC for the purpose of operating the equipment.

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Contents
Overview ...............................................................................................................................................4
GNSS Receiver.................................................................................................................................8
Rubidium Clock .............................................................................................................................10
Power.............................................................................................................................................11
Operation ............................................................................................................................................ 12
GNSS Lock......................................................................................................................................13
Rubidium Discipline......................................................................................................................14
Rubidium Discipline Achieved .....................................................................................................14
Holdover (Portable Calibrator) ....................................................................................................14
GNSS Lock (Reacquire) .................................................................................................................14
Frequency Verification .................................................................................................................14
Functional Controls and Indicators....................................................................................................... 15
LED Indicators...................................................................................................................................... 15
Power.............................................................................................................................................15
Lock................................................................................................................................................15
Ready .............................................................................................................................................16
Holdover........................................................................................................................................16
Battery ...........................................................................................................................................17
Power Good ..................................................................................................................................17
Battery Charge ..............................................................................................................................17
Status Banner/Notification Bar ............................................................................................................ 18
GPS Lock Status and PPS ..............................................................................................................18
Rubidium Status –Lock State ......................................................................................................19
Rubidium Status –Discipline State .............................................................................................20
Temperature .................................................................................................................................21
NR300 Display and Menu Navigation................................................................................................... 22
NEXT and SELECT Buttons, LCD Menus................................................................................................. 22
GNSS Status...................................................................................................................................23
Frequency......................................................................................................................................24

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Rubidium Status............................................................................................................................25
Battery Fuel Gauge.......................................................................................................................26
Battery Charger.............................................................................................................................27
Onboard Sensors ..........................................................................................................................28
User Settings .................................................................................................................................29
Alerts..............................................................................................................................................31
Accelerometer ..............................................................................................................................32
DB9 –RS232/RS485............................................................................................................................. 33
USB Port (Mini B) ................................................................................................................................. 34
USB Power........................................................................................................................................... 34
Frequency Reference Output ............................................................................................................... 35
PPS ...................................................................................................................................................... 35
IRIG-B Output ...................................................................................................................................... 36
AUX ..................................................................................................................................................... 37
IRIG-B Sine........................................................................................................................................... 37
Quick Start Guide................................................................................................................................. 38
Programming Guide (RS232 Port) ........................................................................................................ 40
Accessories.......................................................................................................................................... 43
Antenna .........................................................................................................................................43
Power.............................................................................................................................................44
Technical Specifications ....................................................................................................................... 45
LIMITED HARDWARE WARRANTY ...............................................................................................47

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Overview
The NR300 is a sophisticated timing instrument that has a GNSS disciplined
Rubidium source to provide 10 MHz frequency source with holdover of less <0.5
ppb for over six hours. The unit contains a 26-channel GNSS receiver and
antenna to acquire navigation time to discipline the Rubidium. The unit is factory
configurable to have three 10MHz sine outputs, IRIG-B, and PPS. Unit may also
be used to capture timing events to within 1 usec.
The NR300 is a portable time source for GNSS and GNSS denied environments
with the following capabilities:
●10 MHz output locked to GNSS or atomic holdover.
●NMEA simulator that continues to provide NMEA data even after GNSS loss.
●PPS output that is GNSS derived with atomic holdover.
●Battery powered to provide > 5 hours field use.
●Optional IRIG-B output, modulated and unmodulated.
●Optional auxiliary output.
●Optional event input, with 1us timestamping.
●Built-in drift estimation and measurement.
●Rugged shock protected case.
When locked to the GNSS, the NR300 operates as a standard GNSS locked
frequency reference and PPS source with an accuracy 20 nS. While locked to
the GNSS, the Rubidium internal reference is continually being disciplined in
frequency and its internal PPS is aligned to UTC PPS within <200 ns. If GNSS is
lost, the unit uses the disciplined Rubidium as the master time reference. The
PPS remains aligned to UTC PPS with a drift rate of <40µS/day (procedure
allows for better drift performance).

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Typical drift measurement of Rb PPS [s]
Time and position stamping are optionally available through the event function. A
programmable rising/falling edge causes the current time and position to be
recorded. This data is stored in non-volatile memory and can be read via the
local display. The event data can also be downloaded as a file to be manipulated
off-line. Events are captured and stored to a resolution of 100 ns.
Battery life is a function of configuration and use. The NR300, in its base
configuration, can achieve well over five hours of battery life. The battery
recharges in approximately six to eight hours. Charge status and battery
remaining capacity indicated on the front panel. The battery is accessible and
easily replaced through a removable panel.
Power is provided by either a power adapter (PA0003) or nominal 5Vdc. The
PA0003 operates from 90 to 264 Vac and has a splash proof housing. When not
in use, the power adapter can be stored in the carrying case storage
compartment. The battery is being charged when power is present in the 5Vdc
input port.

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The NR300 case is an extruded aluminum case with impact protection. The
timing platform is shock protected from the case with isolators.
Critical elements in the design are located on a shock/vibration isolated
subassembly.
An active GNSS antenna is provided which is mounted to the top the unit
(Antenna 2). It has a 17 dB LNA to provide gain in low signal environments. The
antenna can be used for GNSS/Rb synchronization in open-air environments.
The antenna input to the GNSS can be easily switched to the external SMA
antenna input (Antenna 1) and a different active antenna can be used. Antenna
status is presented on the front panel screen “GNSS Status”.
To switch between antenna inputs, use the SELECT button on the GNSS
STATUS screen or the USER SETTINGS screen. When the “ANT” field is
highlighted, use the AUXILIARY button to change inputs.
The following output options are available:
●NMEA - RS232, RS485, 115200 Baud, or USB VCOM Port
●10 MHz sine wave - BNC
●PPS - BNC 3.3 Volt CMOS
●Auxiliary Output - BNC (other frequencies) (Event-In)
●IRIG-B (modulated 1kHz or DCLS)
●Event Inputs (1): BNC

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Key Functional Elements

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GNSS Receiver
The receiver and companion elements generate the GNSS sine wave, PPS and
NMEA serial link. The serial link conforms to NMEA 0183 protocol. The GNSS
receiver leverages 12,288 correlators in the baseband processor for low signal
acquisition and tracking. The unit comes with a GNSS antenna with a built- in 28
dB LNA. The local antenna may be detached, and an external antenna used.
The receiver needs at least four satellite vehicles (SVs) visible to obtain an
accurate 3-D position fix. When travelling in a valley, or built-up area, or under
heavy tree cover, you will experience difficulty acquiring and maintaining a
coherent satellite lock. Complete satellite lock may be lost, or only enough
satellites (3) tracked to be able to compute a 2D position fix, or a poor 3D fix due
to insufficient satellite geometry (i.e. poor DOP). It may not be possible to update
a position fix inside a building or beneath a bridge. The receiver can operate in
2D mode if it goes down to seeing only 3 satellites by assuming its height
remains constant. But this assumption can lead to very large errors, especially
when a change in height does occur. A 2D position fix is not considered a good
or accurate fix; it is simply “better than nothing”.
The receiver’s antenna must have a clear view of the sky to acquire satellite lock.
Remember, it is the location of the antenna that will be given as the position fix. If
the antenna is mounted on a vehicle, survey pole, or backpack, allowance for
this must be made when using the solution.
To measure the range from the satellite to the receiver, two criteria are required:
signal transmission time and signal reception time. All GNSS satellites have
several atomic clocks that keep precise time and are used to time-tag the
message (i.e. code the transmission time onto the signal) and to control the
transmission sequence of the coded signal. The receiver has an internal clock to
precisely identify the arrival time of the signal. Transit speed of the signal is a
known constant (the speed of light), therefore: time x speed of light = distance.
Once the receiver calculates the range to a satellite, it knows that it lies
somewhere on an imaginary sphere whose radius is equal to this range. If a
second satellite is then found, a second sphere can again be calculated from this
range information. The receiver will now know that it lies somewhere on the circle
of points produced where these two spheres intersect.

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When a third satellite is detected and a range determined, a third sphere
intersects the area formed by the other two. This intersection occurs at just two
points. A fourth satellite is then used to synchronize the receiver clock to the
satellite clocks.
In practice, just four satellite measurements are sufficient for the receiver to
determine a position, as one of the two points will be totally unreasonable
(possibly many kilometers out into space). This assumes the satellite and
receiver timing to be identical. In reality, when the receiver compares the
incoming signal with its own internal copy of the code and clock, the two will no
longer be synchronized. Timing error in the satellite clocks, the receiver, and
other anomalies mean that the measurement of the signal transit time is in error.
This, effectively, is a constant for all satellites since each measurement is made
simultaneously on parallel tracking channels. Because of this, the resulting
ranges calculated are known as “pseudo-ranges”.
To overcome these errors, the receiver then matches or “skews” its own code to
become synchronous with the satellite signal. This is repeated for all satellites in
turn, thus measuring the relative transit times of individual signals. By accurately
knowing all satellite positions and measuring the signal transit times, the user’s
position can be accurately determined.

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Rubidium Clock
The Rubidium reference employs a coherent trapping (CPT) technique to
interrogate an atomic frequency. A laser illuminates atoms in a resonant cell with
polarized radiation. The laser excitation significantly reduced Rb power
consumption compared to a conventional Rb source plasma cell. A microwave
synthesizer provides the energy for the two sub-bands. Light passing through the
resonant cell is modulated at resonance and the intensity of the light
transmissibility is used to control the microwave frequency. Locked to the atomic
frequency, the microwave frequency is the basis for the 10 MHz generated. The
stability of the source is less than 1 ppb/year which is almost two orders of
magnitude better than a typical OCXO. It is successfully used in applications
where long-term stability is a necessity, but GNSS may not be accessible.
During GNSS lock, the Rb atomic clock output frequency of 10 MHz is
synchronized to the GNSS PPS. The 10 MHz clock drives a counter to generate
a PPS signal. That counter is initially synchronized to the GNSS PPS to within
200 ns. During the discipline period, the Rubidium generated PPS will then
follow the GNSS PPS until “Discipline Good” status is achieved. During this
discipline period, the Rubidium status will show “Discipline Wait” while the
Rubidium source adjusts its frequency output.
Once the full synchronization and discipline has taken place, the PPS accuracy is
dictated by the atomic clock.

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Power
The primary battery pack is a two cell Lithium ion that can be easily replaced
through an access panel.
The internal charger operates either from an external 5Vdc source (4.8 to
5.25Vdc) or a splash-proof charger that operates from 90 to 264Vac.
The charger is housed within the unit. The NR300 is fully functional during
charging with the PA0003 adapter. A full charge takes approximately six to eight
hours.

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Operation
The NR300 is built to provide hours of accurate Rubidium holdover after a period
of GNSS discipline. During this holdover period, the GNSS receiver can be
powered off to reduce power consumption and extend battery life. This is done
with HOLDOVER mode. During Holdover, the Rb module maintains frequency
accuracy of ±0.5ppb/day, providing an ideal source for calibrating systems where
a GPS signal is unavailable. After the NR300 has been used as a calibrator, the
unit can be returned to an area where GNSS signal is available, and the GNSS
can be restarted without disciplining the Rubidium. When the GNSS signal is
reacquired, the Rb frequency can be measured, to verify the integrity of the Rb
source.

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GNSS Lock
On power-up, the first menu “GNSS Status” provides information about the lock
status of the GNSS receiver.
The right side of the display provides UTC time and date indication, as well as a
bar graph showing relative signal-to-noise (SNR) values for each satellite in the
GPS and GLONASS satellite constellations.
The left side of the display includes a tag for both GPS and GLONASS satellite
count, as well as the average SNR of both groups.
Both of these indicator groups provide a quick reference for measuring the
quality of the GNSS lock status. When GNSS lock is achieved, the LOCK LED
indicator is solid green, and Rubidium discipline begins.
PPS Est. Accuracy vs Accuracy Threshold “18/40” [ns]
If the unit indicates “LOCKED”, but the PPS accuracy is not within range, the
“STAT” indicator will flash “ACCY” to indicate the accuracy indicator is beyond
the threshold. The PPS estimated accuracy is listed next to the GAIN indicator
when the unit has GNSS lock. The first number is the GNSS estimate of PPS
accuracy. The second number is threshold, over which the PPS will not be used
for discipline or measurement. If the estimate is greater than the threshold, the
GNSS antenna does not have adequate access to a view of the open sky.

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Rubidium Discipline
During Rubidium discipline, the Rubidium module updates internal loop
coefficients to provide optimal frequency tuning.
When the sample period extends long enough, the Rubidium reports discipline
good.
Rubidium Discipline Achieved
The NR300 illuminates the READY LED indicator. The Rubidium module is now
able to be used as a calibration source in holdover mode.
Holdover (Portable Calibrator)
At this point, the user can press the HOLDOVER button. After confirming with a
long press of the button, the HOLDOVER LED indicator illuminates, and the unit
suspends power to the GNSS receiver, reducing power consumption. The LOCK
indicator shuts off, and the READY and HOLDOVER indicators are lit.
The unit can be taken away from the area where GNSS signal is available and
used as a Rubidium source.
GNSS Lock (Reacquire)
When the NR300 has completed its calibration duties, the unit can be returned to
an area where GNSS signal is available and reacquire GNSS lock. To do this,
press and hold the HOLDOVER button. The screen prompts for confirmation,
then indicates that GNSS power up has been started.
It is important at this point to ensure the unit has adequate GNSS signal to
achieve lock. To verify, return to the GNSS Status menu.
Frequency Verification
Once the GNSS has reacquired lock, the user can navigate to the FREQUENCY
screen by pressing the NEXT button. This screen reports the frequency of the
source as measured against the GNSS PPS.

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Functional Controls and Indicators
LED Indicators
Power
The “Power” LED indicator is illuminated green if the unit is active. If the unit is
not active, the battery status indicators are still operational.
Lock
The “LOCK” indicator is a bi-color LED which provides a quick reference for the
status of the GNSS lock. There are three LOCK conditions which are indicated
as follows by varying green blinking:
When the GNSS is locked and is producing a disciplining PPS to the Rubidium
oscillator, the “GNSS LOCK” indicator will be illuminated solid green. This
indicates that the frequency of the Rubidium is within the threshold loop variance.
A single blink in a green GNSS “LOCK” illumination indicates that the GNSS is
locked and is producing a disciplining pulse to the Rubidium, but the loop
variance is outside the specified parameters, or the Rubidium is not locked. On
startup, one blink indicates the GNSS receiver has acquired a sufficient number
of satellites to generate the PPS pulse. Once acquired, timing can be
maintained with a single satellite.
A double blink in a green “GNSS LOCK” illumination indicates that the GNSS
receiver is not locked, does not have enough satellites for lock, or is tracking
towards lock. The receiver is not producing a PPS to discipline the Rubidium, so
there is insufficient information to determine health of the frequency loop.

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The user should ensure that the unit has access to an open view of the sky, or
the attached antenna has access to open sky.
The GNSS STATUS screen has immediate indication of satellite count, relative
signal strength, and general GNSS lock status.
The Status Banner has indication of presence of PPS. “►” indicates a pulse is
provided to the Rubidium from the GNSS.
Ready
The “Ready” indicator is illuminated if the GNSS has successfully completed
discipline of the Rubidium oscillator. This happens when, after a period of time,
the disciplined Rubidium reports “Discipline Good”. The “Ready” indicator
illuminates, and the status banner shows “DGOOD”. The NR300 is now ready to
enter HOLDOVER.
Holdover
Holdover is mode the unit needs to be in if the instrument is to be used in a
GNSS denied environment. The unit will hold frequency accuracy for < 0.5 ppb.
Actual holdover performance will be measured when the unit is returned to a
GNSS environment. At this point, the unit will measure the actual drift of the
NR300 against the now restored GNSS. If the actual drift exceeds the required
performance, the unit may have been exposed to excessive shock and vibration
or excessive temperature range. Restabilize the Rb by allowing the GNSS to
relock the Rb. The Holdover LED provides a quick indicator that shows if the
Rubidium source has successfully disciplined and is in holdover

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mode. The NR300 provides holdover mode to save power when GNSS lock is
not available. To enter holdover mode, the unit will have successfully achieved
GNSS lock, completed Rb discipline, and the READY indicator illuminated. If the
battery is below 15% capacity - a warning will be shown that you are going into
holdover with a low battery.
Battery
The battery is a 3-cell Lithium ion. It is designed to provide approximately five
hours of service. To achieve maximum service, start with a charged battery
(about six to eight hours of charge time). Be certain you have charged the battery
sufficiently to perform the required holdover time.
Power Good
The “Power Good” indicator illuminates when the adapter input is in an
acceptable range for the charger to provide charge to the battery and run the
system power. If the “Power Good” LED indicator is not illuminated, the power
input is either not present or not in the correct range for the battery charger to
operate correctly. The input power is 5Vdc.
Battery Charge
The “Battery Charge” indicator illuminates when the battery is being charged
from the adapter input power. After a complete charge, the “Battery Charge”
indicator will turn off.
Both the “Power Good” and “Battery Charge” indicators operate whether or not
the unit is powered on.

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Status Banner/Notification Bar
GPS Lock Status and PPS
The status bar has a quick reference indicator for the GPS Lock and its PPS
output. If the GPS is locked, the “GPS” indicator will remain on solid, without
blinking. If the GPS is powered on, but is not locked, the “GPS” indicator will
blink. If no GPS indicator is present, the GNSS receiver is inactive.
When the PPS is detected, the status bar will indicate that the PPS is currently
being provided to the Rubidium for discipline by showing a flashing arrow that
feeds the Rubidium Discipline State indicator.
If the flashing arrow is not present, no PPS is yet available to discipline the
Rubidium. Consider moving the unit to get a better view of the sky.
After the holdover period, and when the GNSS has been powered on again and
GNSS lock has been achieved and the PPS is used to verify the Rubidium
frequency (without discipline enabled), the GPS indicator will show a stopwatch
icon to indicate that the PPS is timing the Rb.
In this mode, the PPS is compared to the Rubidium frequency and therefore is
not provided to the Rubidium for discipline. The user can navigate to the
FREQUENCY menu and verify the current frequency of the Rubidium source. If
the actual drift exceeds the requirement, the ALARM screen may indicate
excessive temperature and or excessive shock and vibration.

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Rubidium Status –Lock State
The status bar provides a snapshot of the current Rubidium status, and its
relationship to the GNSS PPS input.
The status bar will report both Discipline State and Lock State as reported by the
Rubidium module. The default status for the PPS input discipline is Holdover,
until a valid PPS is detected. The Lock State will progress through stages.
Upon power up, the Rubidium enters a heating and initialization period, during
which the status bar reports “INIT” for the Rubidium Lock State. Until the
Rubidium reaches Lock State, the border of the Lock State indicator will flash.
When the Rubidium has initialized, it will begin laser lock, and report “LSRL” on
the status bar. The border around the Lock State will remain flashing.
Within approximately fifteen minutes, the Rubidium module acquires lock,
meaning the output frequency is now locked to the Rb package relative to its
known tuning constants. The status bar Lock State is now “Lock” and the border
no longer flashes.

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Rubidium Status –Discipline State
For reference, the Rb oscillator derives its frequency tuning algorithm constants
from its reference to the GNSS PPS discipline. When the algorithm has sufficient
averaging time from the available PPS, it indicates “DGOOD” for discipline good.
At this point, the NR300 is ready to enter holdover mode.
Prior to discipline good, the Rubidium indicates “DISCP”, which indicates a valid
PPS signal is present, and tuning is in process.
When no valid PPS is present, the Rubidium indicates that the unit is in holdover
condition. The Rubidium considers holdover to be the default state any time a
PPS reference is absent.