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GPS Time and Frequency Time Transfer
The Quartzlock E8000-GPS TT represents a breakthrough in very low noise, traceable, calibration-free GPS Time Transfer, frequency & time standards. These cost effective references maintain the high frequency and time accuracy required for demanding applications. Low distortion 10MHz Sine & 1PPS outputs. The E8000-GPS TT uses a 3 state Kalman filter algorithm to measure & correct the frequency offset of the oscillator with respect to the 1PPS input. Time-tagged 1PPS to 200ps resolution & <12ns jitter. Using two E8000-GPS TT units enables GPS Time Transfer to within ns.
After the successful launch and delivery of the new sub miniature atomic clock (SMAC). Quartzlock is pleased to announce the launch of its new compact portable rubidium frequency reference.
With the growing telecoms infrastructure and increasing number of remote and underground sites requiring high accuracy references for maintenance and service Quartzlock has developed a compact light weight portable rubidium frequency reference with a size of 103(w)x55(h)x122(d)mm and weighing less than 500g. The E10-P can be used as a hand held rubidium frequency reference.
The E10-P is a new, low-cost portable timing reference source based on Quartzlock’s SMAC Rubidium clock technology. It is designed for telecom and metrology test and measurement applications. The Rubidium clock provides highly accurate, stable and reliable output signal. Its fast warm-up eliminates the need of bulky backup batteries.
The Standard 10 MHz reference source is provided for metrology and calibration laboratory equipment such as universal counters, spectrum analyzers and synthesized signal generators.
Quartzlock A7-MX Frequency Analyser
A quasi real time plot of the Phase Spectral Density (PSD) has been added to the A7-MX virtual front panel. This shows phase noise as a graph of L(f) in units of dBc against offset frequency on a log scale. Various window functions and averaging modes are provided. The routines are identical to those used in the Industry standard software "Stable32".
The user can select the basic length of the FFT, and also the degree of overlap. As data is accumulated, new FFTs are performed on a mix of old and new data depending on the overlap parameter. For example, with an FFT length of 256 points, and an overlap of 50%, with a tau (sample rate) of 10ms, a new FFT will be available every 1.28 seconds.
Each FFT result can either replace the last graph, be added to a block average, or be used in a continuous or exponential average.
All FFTs are correctly normalised for bin noise bandwidth, window coherent gain, and nominal frequency.
Frequency data always has a fixed offset removed before being used for the FFT calculation. Phase data has a fixed slope ramp removed by linear regression. This avoids a large component in the lower frequency bins which will distort the result, even when windowing is used.
Phase noise measurement at very small frequency offsets
Identification of spurious components in the data which can distort an Allen variance plot
Maximum offset frequency 500Hz (at 1ks/s)
Close-in Phase Noise floor typically
-105dBc/Hz @ 50mHz offset (0.05Hz offset)
-115dBc/Hz @ 100mHz offset (0.1Hz offset)
-135dBc/Hz @ 1Hz offset
-150dBc/Hz @ 100Hz offset.
New: passive and active hydrogen maser frequency standards and associated instruments are excellent technologies available today. These units have been built in substantial quantities and by special request; the performance of the instruments can be independently certified by NIST (USA), PTB (Germany) or NPL (UK).
The Active Hydrogen Maser technology provides the best known frequency stability for a frequency generator commercially available today. Active masers will be used when the best stability is needed in a time domain of 1 sec. to a day. At a 1-hour averaging time, the Active Maser exceeds the stability of the best known cesium oscillators by a factor of at least 100. Unlike cesium oscillators, Hydrogen Masers have no physics wear-out mechanism. They have the inherent ability to operate for 10 years, although failures earlier than 10 year can be attributed to ion pumps, the dissociator, and the hydrogen source. Even if such maintenance is needed, the costs will be a factor of 10 less than the cesium beam tube replacement, which will occur in the five to ten years life of the equipment.
The Passive Hydrogen Maser principle of operation is based on a 5 MHz quartz crystal oscillator, frequency locked to the hyperfine transition of the hydrogen atom. The Passive Maser is specifically designed to provide an alternative technology to the high performance option cesium oscillators -- the Maser's stability specification is a factor of 10 better than the best known cesium oscillator. The Maser's 5-year overall accuracy of <1.5x10-12, exceeds the best cesium specifications of 1.5x10-12 accuracy in light of the 3-year life warranty of the beam tube.
Replacement costs of a cesium beam tube generally are costly. Hydrogen Masers, however, have no physics wear-out mechanism. The maser has the intrinsic capability to operate for ten years, although failures earlier than 10 years are sometimes related to ion pumps, the dissociator, and the hydrogen source. Even if replacement of these components should prove necessary, they would cost a factor of 10 less than cesium beam tube replacement. In light of the above, the Passive Maser may be the number one choice over high performance option cesium oscillators when better stability and competitive accuracy are needed at a comparable sales price, while at the same time reducing the 10-year life cycle costs.
In conclusion, a great deal of research is underway to improve present frequency standards. The challenge, however, continues to lie in the ability to improve crystal oscillators and low-cost atomic standards such as rubidium. Meeting this challenge is crucial for 21st century communication systems, computer networks, navigation and transportation systems including avionics, electric power systems, space exploration, astronomy and astrometry, geodesy, geology, earthquake monitoring and many others.
The A7-MX has isolated inputs and the world's highest frequency/phase resolution plus phase noise measurement (50fs single shot, very low noise s1s<5x10-14).
Automatic high resolution (50fs) frequency and phase comparator, the Quartzlock A7 MX, enables fast comparisons (1000 readings /sec) and adjustment between frequency standards and oscillators. Close in phase noise to low levels of measurement is also featured. Easy to operate, the A7-MX is for lab or production test use. Selectable filters, resolutions and tau's are standard. Just press 'ON' for instant plots in real time.
Updates from 1ms to 1000s gate times.
Quartzlock's new version of the national lab A7-MX (metrology) comparator enables 1x10-16 resolution of the frequency difference between two standards. The A7-MX has noise reduction filters which are selectable by simple front panel control, as is resolution ranging from 1x10-6 to 1x10-13 for analogue meter reading and resolution to 1000x with the internal time interval counter (A7-MX forms a National Laboratory level metrology system suitable for leading research projects with x10-17 resolution at 104 averaging time). Measurement times to 1000s enable drift tests to >1 year. A7-MX stores 32,000 data points internal and is unaffected by pc crashes. 24V dc BBU enables long term testing.
The new units have isolated inputs to avoid local lab noise problems and earth loops. Counter discrimination is 12.2 picoseconds and 15 to 32 femtosecond single shot resolution, limited only by instrument noise. 1ps/hour drift is typical with 2ps/C temp stability and 5ps/day drift.
A7-MX ATE version enables test solution system development and automatic production test use.
Crash proof "inside A7-MX data storage" does not rely on the PC software.
Glitchless, uninterruptible PSU facility has low noise 115/230 V as PSU, external 24 V input dc (BBU) for auto seamless switching in case of ac failure, or select dc in case of lab supply noise problems to ensure trouble free long measurement runs. External computer enables you to update PC in future to take advantage of higher processing speeds and large display.
Another new Quartzlock development is the GPS disciplined BVA oscillator frequency standard/calibration reference.
The new quad helix antenna and down converter in 2nd generation carrier phase tracking GPS eliminates multipath timing errors and has microphase stepper with 1ns steps built-in to offset ant/cable and ionospheric delays. The latest A8-MX (2006) from Quartzlock exhibits timing accuracy and short-term stability previously unheard of in telecoms and calibration lab applications. The Quartzlock A8-MX GPS Frequency and Time Standard is probably the smallest and lightest unit available. Long term performance equal to UTC @ 5x10-14 offset (long term), NIST and NPL traceable by satellite time transfer techniques.
Performance of today's GPS-OCXO now equals or exceeds primary cesium reference (commercial) clocks. Production test of Quartzlock A8 GPS series calls for the Active Hydrogen Maser Quartzlock use to give quality assurance departments confidence in measured values. Short-term stability is to 8x10-14 and one-day drift / offset figures, typically 5x10-14. Sine and Square 1MHz, 5MHz, 10MHz and 1pps outputs are provided. Time and date, position to ±2m, SAT DATA, 1pps micro phase step, DAC#, ESTDt + Df are all displayed.
The Quartzlock Time and Frequency Standards Laboratory is one of very few commercial laboratories in the world able to certify performance to this level using a maser based timing system.
(This article appeared in the March 2004 edition of Microwave Product Digest – www.mpdigest.com)
Rubidium Time and Frequency Standards - Instruments & Components
The first Rubidium frequency standard originated from the work of Carpenter (Carpenter et al, 1960) and Arditi (Arditi, 1960). It was a few years until the first commercial devices appeared on the market and this was primarily due to the work of Packard and Schwartz who had been strongly influenced by the work of Arditi on Alkali atoms (of which Rb87 is one), a few years before. Unlike much of the research done on frequency standards at that time, practical realization of a rubidium maser was high on the researchers agenda. This was mainly due to an understanding that such a device would have extremely good short-term stability relative to size and price. In 1964, Davidovits brought such research to fruition, with the first operational rubidium frequency standard.
A rubidium frequency standard owes its outstanding accuracy and superb stability to a unique frequency control mechanism. The resonant transition frequency of the Rb87 atom (6,834,682,614 Hz) is used as a reference against which an OCXO output is compared. The OCXO output is multiplied to the resonance frequency and is used to drive the microwave cavity where the atomic transition is detected by Electro-optical means. The detector is used to lock the OCXO output ensuring its medium and long-term stability.
The Rubidium frequency standard essentially consists of a voltage controlled crystal oscillator, which is locked to a highly stable atomic transition in the ground state of the Rb87 atom. The rubidium frequency standard may be thought of as consisting of a cell containing the rubidium in its vapor state, placed into a microwave cavity resonant at the hyperfine frequency of the ground state. Optical pumping ensures state selection. The cell contains a buffer gas primarily to inhibit wall relaxation and Doppler broadening.
Like its more expensive cousin, the hydrogen maser, it may be operated either as a passive or as an active device. The passive rubidium frequency standard has proved the most useful, as it may be reduced to the smallest size while retaining excellent frequency stability. The applications for such a device abound in the communication, space and navigation fields.
There are several reasons why Rb has an important role to play as a frequency standard. Perhaps most significantly is its accuracy and stability. Accuracy is comparable with that of the standard caesium with an operating life approximately 5 times that of Cs. Furthermore, the cost of a replacement physics package is minimal. In addition, the stability of an Rb frequency standard over short time-scales -100s of seconds- betters that of Cs (Cs are more stable over longer time periods, in the regions of hours to years). At 100s the frequency stability of the best performing Quartzlock Rb is 3 x 10-13, better than a standard caesium beam tube. The phase noise of the Quartzlock Rb is -150 dBc/Hz @ 10 kHz from the carrier.
A draw of Rb as a frequency standard in the past, included the limited life of the Rb lamp, however, this has since improved to >10 years. Thermal stability of the Rb is also slightly inferior to that of Cs or H Masers. The cost of a rubidium frequency standard, however, is significantly less expensive than a Cs, with a much reduced size and weight. Due to its small size, low weight and environmental tolerance, the Rb frequency standard is ideal for mobile applications. Indeed, Rb atomic clocks are being used in the new generation of GPS satellites. This is in part due to the extended life of the Rb physics package. The Rb is also extremely quick to reach operational performance, reaching 5x10-10 within 5 minutes.
The Quartzlock A10 is the only rubidium frequency standard providing the user with 1, 5 and 10 MHz sinewave and squarewave outputs from the front panel. Also included on the front panel is a 1pps output, enabling the user to turn the Rb frequency standard into a clock. At the rear of the device, six 10 MHz highly buffered outputs are provided. Although the rear panel outputs are factory set at 10 MHz, simple alterations made inside the unit (easily performed by even the novice) can turn this into either 5 or 1MHz. The flexibility afforded by the A10 is unsurpassed.
Due to Quartzlock's wide range of products and expertise, a further improvement is possible using the Quartzlock A8 carrier phase tracking GPS. By inputting a 1pps signal from the A8 GPS to the rear of the unit, the A-10 may be transformed into an extremely accurate and stable GPS disciplined Rubidium.
Recently Quartzlock has been awarded a major European research and development award. The CRAFT project, for example, among others, will enable further research and development of the company's Rb frequency standard. Just recently, an entirely new electronics package has been developed in Falmouth and it is estimated that Quartzlock's production of Rubidium will expand rapidly.
Naturally, the applications for such a low cost, small size device with excellent short-term accuracy are many. It may be used in frequency calibration, telecom network synchronization, cellular phone base stations, satellite navigation and GPS receivers, TV broadcasting, radio transmitters, ground and satellite communications, time base and calibration, secure communications and spread spectrum techniques and radio navigation.
(This article first appeared in the March 2006 edition of Microwave Product Digest – www.mpdigest.com)
Recent Design Innovations in Rubidium and BVA Based Time and Frequency Standards
In a world dominated by technology, the need for accurate and reliable frequency and time standards has risen dramatically. The market consists of a variety of devices varying in accuracy, stability and price, including traditional oscillators to medium and high performance atomic frequency standards, including GPS, Rubidium, Cesium Beam and Hydrogen Masers.
Crystal oscillators are among the most important electronic components in use today and are second only to the atomic sources as the most stable frequency devices. Most complex electronic systems rely on a crystal oscillator to provide a stable reference so that other frequencies of the system can be compared to or generated from this reference. More than 1 billion quartz crystal oscillators are produced annually for a variety of applications.
The BVA SC cut OCXO is the most stable quartz oscillator available. When the very high short term stability of BVA is added to a carrier phase tracking GPS and quad helix antenna to avoid multi-path, then near passive hydrogen maser performance is realized.
The range of different oscillator types includes simple uncompensated oscillators (XO), temperature compensated (TCXO), microcomputer compensated (MCXO), voltage compensated (VCXO) and oven controlled (OCXO), including double-oven designs.
Each has advantages and disadvantages. The best oscillator for a given application is determined by a variety of factors, including frequency and accuracy, drift, phase deviation, phase noise, warm-up time and perhaps most important, price. The cost of crystal oscillators varies greatly between the simple XO and the much more accurate and stable OCXO or BVA OCXO.
When a higher degree of accuracy is required, however, atomic clocks easily outperform any traditional oscillator except only in the case of a GPS disciplined BVA.
A rubidium frequency standard owes its outstanding accuracy and superb stability to a unique frequency control mechanism. The resonant transition frequency of the Rb87 atom (6,834,682,614 Hz) is used as a reference against which an OCXO output is compared. The OCXO output is multiplied to the resonance frequency and is used to drive the microwave cavity where the atomic transition is detected by electro-optical means. The detector is used to lock the OCXO output, ensuring its medium and long-term stability.
The rubidium frequency standard essentially consists of a voltage controlled crystal oscillator, which is locked to a highly stable atomic transition in the ground state of the Rb87 atom. The rubidium frequency standard may be thought of as consisting of a cell containing the rubidium in its vapor state, placed into a microwave cavity resonant at the hyperfine frequency of the ground state. Optical pumping ensures state selection. The cell contains a buffer gas primarily to inhibit wall relaxation and Doppler broadening.
The rubidium frequency standard may be operated either as a passive or as an active device. The passive rubidium frequency standard has proved the most useful, as it may be reduced to the smallest size while retaining excellent frequency stability. The applications for such a device abound in the communication, space and navigation fields.
Through the years, advances in rubidium standards have increased dramatically; now very low power (3W) small size 144cc are available with latest XT Rb.
For example, Quartzlock's A10 HPRO component, or A10-M (HPRO) instrument, has 100 times better stability at 10MHz than most rubidium oscillators, lower phase noise by 10 to 20 dB and comes with certified offset (accuracy), ISO 9001, calibration certificate, C of C + NPL traceable stability plots. The 10MHz output exhibits typically 3x10-13 stability at measurement times of 200 to 2000 seconds. A space qualified version is also offered. Typically the phase noise of the space qualified and terrestrial HPRO is currently -120dBc/Hz @ 1Hz offset, 145dBc/Hz @ 100Hz and 160dBc/Hz @ 10kHz. Satcom and high stability microwave source referencing requirements are met.
Glitchless, uninterruptible PSU facilities include low noise 115/ 230V AC PSU, external DC 24 V input with seamless switching, automatically in case of AC failure, or selection in case of lab supply noise problems to ensure trouble free long measurement runs.
In addition, a low profile 10MHz rubidium frequency reference has special versions with 4x10-13/ 100s, 3x10-13/ 200 to 2000s stability, low noise to -160dBc/Hz and 10-12 offset on shipment. The A10-LPRO comes with -20 + 65°C temperature range, full CE, milspec FRS version, DKD compliance, NIST certified accuracy, ISO9001 Certificate of Conformance and NPL traceable STS. The new unit has excellent vibration resistance (Nato stock number: 5820-99-855-3030) when fitted in A10-M.
Applications include: Telecom sync, SatCom, Radio Netsync, calibration, test solutions, precise frequency referencing, calibration and cellular base station referencing.
The Economy spec telecom version has 2E-12/100s stability, 4E-10 aging/year, Tempco in 3E-10/-10 + 55°C and 22 to 30 Vdc supply at 10 Watts consumption.
The rubidium oscillator is based on new space qualified R&D work. The oscillator has high vibration and EMC resistance.
Atomic clock compatible instruments for new standards laboratories and telecoms network synchronization that require increasingly future proof solutions have also been developed. Higher stability reference performances are debilitated and corrupted by poor distribution amplifiers whose temperature stability, isolation and noise floors are not specified. The A5-32 will not become obsolete as users upgrade to cesium, H-maser or next generation H-maser, HSRO (High Stability Rubidium Oscillator) and GPS-Rb, GPS-BVA & XT Rb calibration references.
Features include: Phase stability, 10ps/C, 110dB isolation, x10-16 stability and -140 dBc/Hz @ 1Hz phase noise.
With tuned output option frequency response is equivalent to a single pole bandpass filter centered on the specified frequency and with a 3dB bandwidth of 7%. Centre frequency specified between 1 MHz and 100 MHz.
Time & frequency standards
Real-time Allan variance plotting.
The Quartzlock frequency and phase analyser, model A7-MX (broadband), compares 5MHz or 10MHz or 50kHz to 65MHz signals, plotting realtime Allan varience (AVAR), absolute & relative frequency difference and phase data for onward analysis by industry standard stable 32 into phase noise, MDEV, MTIE, etc.
Oscillator & signal source development with production test applications depend on fast measurement of phase datato realise short term stability AVAR, relative & absolute frequency & other modified AVAR.
The main benefit is a 40% reduction in oscillator R&D time with ability for many oscillator manufacturers to specify Allan Variance for the first time & enhance the users product specification in expanded terms. Other benefits include the ability to plot very close-in Phase Noise using Stable 32 from 1mHz offset. Very fast measurement time & highest resolution, <5e-14/s in 200Hz BW available because of the achievable & usable low noise level & 50fs single shot measurement with 'no dead time' stroboscopic phasemeter technology.
Realtime plotting of short term measurements selectable from 1ms to 2000s & up to 32,000 data points (i.e. up to over 2 years for Drift / Aging parametrics)
Selectable tau, filters, mode, multiplier & analog range's (10ps to 1us / E-13 to E-8 / division on the large analog meter that is unbeatable still for oscillator frequency adjustment to E-12 & E-13 resolution).
A7-MX product details