6688/6689
High Stability Frequency Standards
- Category: High Stability Frequency Standards
- Manufacturer: Pendulum Instruments
- Frequency outputs (10 MHz): 5 (668X/011) or 10 (668X/021) sine outputs
- Frequency output (5 MHz): 1 sine output
- Output level / impedance: sine > 0.6 Vrms in 50 Ω
- 6688 calibration uncertainty (+23 ±3 °C): 5×10⁻⁹
- Data sheet: Download PDF
- External link: Official product page
Overview
The Pendulum Instruments 6688/6689 High Stability Frequency Standards are stand-alone units designed for test environments where several instruments have to share one precise reference. The 6688 uses a high-stability SC-cut oven-controlled crystal oscillator (OCXO), reaching a calibrated frequency uncertainty of 5×10⁻⁹, a short-term stability (Allan deviation, τ=1 s) better than 5×10⁻¹² and a monthly aging rate of only 3×10⁻⁹; the 6689 has a built-in rubidium clock with a calibration uncertainty of 5×10⁻¹¹, a monthly aging rate as low as 5×10⁻¹¹ and total aging of no more than 1×10⁻⁹ over ten years, so it can serve as a laboratory primary reference. Both models offer 5 or 10 buffered and isolated 10 MHz sine outputs (> 0.6 Vrms in 50 Ω) plus one 5 MHz output, accept any supply from 100 to 240 V automatically, and comply with CE safety and EMI requirements. At only 315×86×395 mm and 4.8 kg, they make an ideal frequency distribution core for test systems and calibration laboratories.
Key features
- Multiple buffered, isolated outputs — The standard configuration provides 5 10 MHz outputs (/011 version) or 10 10 MHz outputs (/021 version) plus one 5 MHz output. The outputs are isolated from one another, so up to eleven instruments can be driven at once without interference.
- Very high short-term stability — The Allan deviation of the 6688 OCXO is better than 5×10⁻¹² at τ=1 s; the 6689 rubidium clock reaches 3×10⁻¹¹ (τ=1 s), meeting the demands of exacting frequency measurement and calibration work.
- Rubidium primary reference (6689) — The 6689 has a built-in rubidium clock whose total aging over ten years is no more than 1×10⁻⁹ (about 0.001 ppm), so it can act as the primary reference for frequency counters, synthesizers and similar equipment in a calibration laboratory.
- Fast warm-up, usable in the field — The 6688 OCXO needs only 10 minutes to warm up to 5×10⁻⁹ stability and the 6689 rubidium clock locks in about 5.4 minutes. Warm-up that short also makes the units practical to carry out to a measurement site.
- Automatic wide-range supply — The supply accepts 100 to 240 V (±10%) worldwide without a manual selector, and complies with CE safety certification (EN 61010-1) and EMI requirements (EN 55011 ISM Class B).
- Core of an automatic test or calibration system — Designed for automatic test systems (ATS) on telecommunications production lines and for calibration laboratories, a single unit acts as the frequency distribution centre for a whole test rack, simplifying the system and keeping every instrument on the same frequency.
Typical applications
- Automatic test systems in telecommunications manufacturing — On a telecommunications production line, one 6688/6689 supplies a stable 10 MHz reference shared by as many as 11 automatic test instruments, so results from every line are comparable and traceable and no instrument needs a reference of its own.
- A stand-alone frequency reference where there is no GPS signal — In a shielded room or a basement metrology laboratory where GNSS satellite signals cannot be received, the 6688/6689 acts as a stand-alone high stability frequency standard, providing long-term stable 10 MHz and 5 MHz reference outputs with no dependence on external satellite timing and meeting traceability requirements for calibration and measurement.
- R&D bench and portable field frequency reference — An R&D engineer needs one common reference clock on the bench for frequency counters, signal generators and network analyzers. The 6689's built-in rubidium clock meets specification after a 10 minute warm-up and can also be carried to site for high stability measurements, cutting the wait before on-site calibration considerably.
Key specifications
Key specifications for 6688/6689, as published by Pendulum Instruments. For the full datasheet or a customized configuration, please get in touch.
| Frequency outputs (10 MHz) | 5 (668X/011) or 10 (668X/021) sine outputs |
|---|---|
| Frequency output (5 MHz) | 1 sine output |
| Output level / impedance | sine > 0.6 Vrms in 50 Ω |
| 6688 calibration uncertainty (+23 ±3 °C) | 5×10⁻⁹ |
| 6688 aging rate (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, +25 °C) |
| 6689 calibration uncertainty (+23 ±3 °C) | 5×10⁻¹¹ |
| 6689 aging rate (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) |
| Supply voltage / power consumption | 100 to 240 V ±10%; 6688 <20 W at warm-up / <7 W continuous; 6689 <70 W at 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 | 315×86×395 mm / 4.8 kg (net) |
Frequently asked questions
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