SR625 Frequency Counter —
with Rb Timebase
Features:
Rubidium atomic timebase
2 GHz prescaler input
11-digit frequency resolution (1 s)
10 MHz Rb timebase output
Statistical analysis & Allan variance
GPIB and RS-232 interfaces
The SR625 Frequency Counter is a NIST traceable frequency counting standard for calibrating base stations, transmitters and many other types of communication systems. It combines the high resolution and wide variety of features found in the SR620 counter with the atomic accuracy of a rubidium timebase.
Low Drift, High Accuracy
The SR625 Frequency Counter consists of a frequency counter (SR620), a high-accuracy rubidium timebase (PRS10), and a 2 GHz input prescaler. The combination of the SR620 and the prescaler allows direct frequency measurements up to 2 GHz with twelve digits of resolution in a 100 s measurement.
The rubidium timebase ensures excellent short-term stability (<2 × 10-11 Allan variance (1 s)) and long-term drift (<5 × 10-11/month).
Simple, Portable Operation
The SR625's warmup time is less than ten minutes making it ideal for field applications. An additional back-panel output provides a rubidium stabilized 10 MHz signal which can be used to drive other test equipment (e.g., synthesizers or spectrum analyzers). The standard GPIB and RS-232 interfaces allow for complete control and data acquisition from any laboratory computer. The SR625's performance makes it the standard for remote applications or laboratory calibration.
Specification:
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The following specifications relate to the 2.2 GHz prescaler and the rubidium timebase of the SR625. Please see the section on the SR620 for general specifications relating to the counter.
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Rubidium Timebase
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Frequency
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10 MHz
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Accuracy at shipment
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±5 × 10-11
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One day stability
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4 × 10-11/day
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Long term drift
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<5 × 10-11/month, <5 × 10-10/year
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Short term stability
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1 s Allan variance
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<2 × 10-11
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10 s Allan variance
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<1 × 10-11
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100 s Allan variance
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<2 × 10-12
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Warmup interval
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10 minutes to meet short-term stability specification
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Power consumption
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70 W (at warmup), 100/120/208/240 VAC, 50/60 Hz
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Output
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10 MHz, 1 Vpp sine wave
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Prescaler
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Frequency ratio
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10:1
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Input impedance
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50 Ω
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Max. input level
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+23 dBm
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Input freq. range
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50 MHz to 2.2 GHz
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Input sensitivity
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See graph in Features section
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Output
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Output load
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50 Ω
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Output amplitude
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700 mVpp square wave
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Output offset
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500 mV
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General
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Size
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17" × 3" × 14.5" (WHL)
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Weight
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15 lbs.
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Warranty
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One year parts and labor on defects in materials and workmanship
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SR620 Frequency Counter
Features:
25 ps single-shot time resolution
1.3 GHz frequency range
11-digit frequency resolution (1 s)
Statistical analysis & Allan variance
Graphical output to XY scopes
GPIB and RS-232 interfaces
Ovenized timebase (opt.)
The SR620 Time Interval Counter performs virtually all of the time and frequency measurements required in a laboratory or ATE environment. The instrument's single-shot timing resolution and low jitter make it the counter of choice for almost any application.
SR620 Measurements
The SR620 measures time interval, frequency, pulse-width, rise and fall time, period, phase and events. Time intervals are measured with 25 ps rms resolution, making the SR620 one of the highest resolution counters available. Frequency is measured from 0.001 Hz to 1.3 GHz, and a choice of gates ranging from 1 period to 500 seconds is provided. The SR620 delivers up to 11 digits of frequency resolution in one second, making it suitable for measurement applications ranging from short-term phase locked loop jitter, to the long-term drift of atomic clocks. All measurement modes are supported by a wide variety of flexible arming and triggering options.
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