Pendulum Instruments · High-Stability Frequency Standards
6688/6689
Stand-alone high-stability frequency references built around an OCXO or a rubidium clock, feeding up to eleven instruments at once
Not every site can see the sky. Basement labs, shielded rooms, ships and vehicle racks get no GNSS, so they need a reference that runs on its own signal, and that is what the 6688 is for. Choose an OCXO or a rubidium core, with 5 (668X/011) or 10 (668X/021) outputs of 10 MHz sine plus one 5 MHz output, enough to drive up to eleven instruments from one box. The 6688 is calibrated to 5×10⁻⁹ (+23 ±3 °C) and ages 3×10⁻⁹ per month. The buying question is how long you can go between calibrations, because the aging rate decides how fast it drifts out of your tolerance.
Overview
A stand-alone reference and a GNSS-disciplined one differ in time scale, not in instantaneous accuracy. A disciplined unit is corrected continuously by the satellite signal and does not wander over the long term. A stand-alone unit starts drifting at its aging rate the moment it leaves the calibration bench, so its accuracy is a function of time since the last calibration. That is a trade, not a flaw: in return you get no dependence on any external signal, ready output at switch-on, and no antenna runs or reception problems to manage. With 3×10⁻⁹ per month, 2×10⁻⁸ per year and a calibration uncertainty of 5×10⁻⁹, the 6688 covers most lab and production-line needs, and the calibration interval can be planned from those numbers. The >0.6 Vrms / 50 Ω sine output is the standard reference input of most instruments; pick 5 or 10 outputs by counting what sits in the rack. Typical homes are shielded environments, mobile platforms, and labs that want a second, independent reference to cross-check a GNSS-disciplined one.
Key specifications
| Frequency outputs (10 MHz) | 5 (668X/011) or 10 (668X/021) sine outputs |
|---|---|
| Frequency output (5 MHz) | 1 sine output |
| Output level / impedance | >0.6 Vrms / 50 Ω |
| 6688 calibration uncertainty (+23 ±3 °C) | 5×10⁻⁹ |
| 6688 aging (month / year) | 3×10⁻⁹ / 2×10⁻⁸ |
| 6688 short-term stability (ADEV, τ=1 s / τ=10 s) | 5×10⁻¹² / 5×10⁻¹² |
| 6688 warm-up time | 10 minutes (to 5×10⁻⁹ of the final value, +25 °C) |
| 6689 calibration uncertainty (+23 ±3 °C) | 5×10⁻¹¹ |
| 6689 aging (month / 10 years) | 5×10⁻¹¹ / 1×10⁻⁹ |
| 6689 short-term stability (ADEV, τ=1 s / τ=10 s) | 3×10⁻¹¹ / 1×10⁻¹¹ |
| 6689 warm-up time | 5.4 minutes to lock; 10.6 minutes to 4×10⁻¹⁰ (+25 °C) |
| Line voltage / power consumption | 100 to 240 V ±10% (90 to 264 V), 47 to 63 Hz; 6688 <20 W warm-up / <7 W continuous; 6689 <70 W warm-up / <30 W continuous |
| Operating / storage temperature | 0 °C to +50 °C / -40 °C to +70 °C |
| Dimensions (W x H x D) / weight | 315 x 86 x 395 mm / 4.8 kg (net) |
Features
No external signal needed
No antenna and no reception issues; it is ready at switch-on in shielded rooms and basement labs.
OCXO or rubidium core
Pick by the stability and budget you need; the chassis and output layout are the same.
One unit fills the rack
5 or 10 outputs of 10 MHz plus one 5 MHz output drive up to eleven instruments in step.
Aging sets the calibration interval
3×10⁻⁹ per month and 2×10⁻⁸ per year let you plan recalibration from numbers instead of habit.
Standard output interface
A sine output above 0.6 Vrms into 50 Ω connects straight to the external reference input of any brand of instrument.
The core of a system
Telecom production ATE and calibration labs need one common frequency source; a single 6688 fills that role and saves a reference at every test station.
Typical applications
Telecom production
Automatic test systems in telecom equipment production
On a telecom production line one 6688/6689 gives up to 11 automatic test instruments a shared, stable 10 MHz reference, so results from every line compare and trace back to one source without a reference at each instrument.
Metrology lab
Stand-alone frequency reference where no GPS signal is available
In shielded rooms and underground metrology labs with no GNSS reception, the 6688/6689 supplies long-term stable 10 MHz and 5 MHz outputs without any satellite timing, meeting the traceability needs of calibration and measurement work.
R&D engineering
R&D bench and portable field frequency reference
Engineers need one clock behind their counters, signal generators and network analyzers. The 6689 with its rubidium clock reaches specification after about 10 minutes of warm-up and can also travel to the field for high-stability work, cutting the wait for on-site calibration.
Options and configuration
Tick the options you need; we compile the configuration list and carry it into the quote form.
Model selection (oscillator reference)
Output and mechanical options
Calibration and warranty options
Downloads
Need pricing, specifications or lead time for 6688?
Also available for rent: 6688 is part of the Pendulum rental program, for project peaks, calibration backup and pre-purchase trials. Rental inquiry →