GNSS and GPS Locked 10 MHz Frequency References for Time and Frequency Synchronization
Major issue for references in multi-site digital systems is site to site synchronization. This invariably leads to a GNSS locked reference. In addition to the GNSS locked 10 MHz reference, the GNSS locked reference also provides PPS pulse that is also used for synchronization.
Another concern in these applications is holdover performance. Holdover is the operating mode the reference enters when GPS is lost. The concern is: how much drift will occur during the holdover period and what will the transition from the GPS loss to GPS locked state be like? Typically, holdover tolerances are on the order of 5 ppb/day ~50 ppb/year. Obviously, better performance can be purchased. The holdover transition becomes a function of the OCXO set point when GNSS is lost. If the OCXO set point is signicantly different from 10 MHz, then there will be a frequency transient when the GNSSDO transitions.
To address this issue, Novus references incorporate a memory device that stores the latest OCXO correction coefficients in FLASH memory. The coefficients are typically less than 24 hours old and, as a result, there is a minimal frequency transistion and long-term holdover drift is effectively eliminated. To achieve reasonable noise levels an OCXO is disciplined to the GPS. There are GPSDO's available that are TCXO based and lower cost. But the holdover performance and noise is typically unacceptable for most applications.
Another important feature is the type of power used. While AC power is very common, many installations use DC power, such as -48 Vdc. Novus offers references that can be powered from -60 to +60 Vdc. All products can be purchased as a kit (kit includes GPSDO, antenna, power supply and cable -everything you need to get your reference running).
Novus GPSDO Summary- All have PPS and RS232 NMEA
|Number of Outputs||Rack Mount||Compact||PCB Assembly||Portable||Power|
|NR3620-CAL||1||•||± 60 vdc"|
|NR1110-O||4||•||85 to 260 vac|
|NT6700-NTP||4||•||85 to 260 vac|
|NR2410-O||2||85 to 260 vac|
|NT9400||2||•||85 to 260 vac|
|NR2310-G||10||•||85 to 260 vac|
*AC Power Adapter Available
Kits Available for All Models (Antenna, Cable, Power Supplies)
General purpose triple channel GNSSDO. Low noise OCXO based reference offers 10 MHz, NMEA and PPS. Status relays can be wired into an alarm panel to alert of a failed self-test condition or if the unit cannot achieve GPS lock. Wide power operating range includes -60 to +60 Vdc (in three ranges). Auto-Calibration feature stores the most current OCXO compensation coefficients.
Single Channel GPS locked OCXO, 10 MHz frequency reference with PPS, RS232. The unit features Auto-Calibration such that the most recent coefficients to compensate the OCXO for drift due to aging and/or temperature are stored and applied to the OCXO during GPS loss of lock conditions. High performance 26 channel GPS receiver that Supports GPS, GLONASS, SBAS, QZSS. By being able to receive data from multiple satellite constellations lower lock time is achieved. With twice the number of satellites in view, as a GPS only configuration, achieving and maintaining lock in poor signal environments is enhanced.
Four channel GPSDO meets the synchronization needs for more complex systems. PPS and NMEA signals come standard. Large LCD display presents time and unit status. External event input (3.3 vdc logic) causes the current time and position to be recorded and stored. The event data can also be e-mailed to a user defined IP address. Optional NTP time server provides precise timing for a local equipment network. GPSDO features low noise OCXO and Auto-Calibration.