Frequency Counters
SR625 Rubidium stabilized frequency counter
· Rubidium atomic timebase
· 2 GHz prescaler input
· 11-digit frequency resolution (1 s)
· Short 10 minute warm-up period
· Portable operation
· 10 MHz Rb timebase output
· Statistical analysis & Allan variance
· Hardcopy to printers and plotters
· GPIB and RS-232 interfaces
· SR625 ... $14,850
(U.S. list)
Stanford Research Systems phone: (408)744-9040
www.thinkSRS.com
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 SR620 Time
Interval/Frequency Counter plus a high-accuracy rubidium
timebase and 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 second gate. The rubidium timebase ensures both
excellent short-term stability (<2 × 10
−11
Allan variance (1 s))
and low 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 such as 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.
SR625 Time Interval/Frequency Counter
www.thinkSRS.com
The SR625 combines a SR620 Time Interval/Frequency
Counter with a rubidium timebase and a 2.2 GHz prescaler.
The following specifications relate to the 2.2 GHz prescaler
and the rubidium timebase only. Please see the section on the
SR620 for general specifications relating to the counter.
Rubidium Timebase
Frequency 10 MHz
Accuracy at shipment ±5 × 10
−11
One day stability 4 × 10
−11
/day
Long-term drift <5 × 10
−11
/month, <5 × 10
−10
/year
Short-term stability
1 s Allan variance <2 × 10
−11
10 s Allan var. <1 × 10
−11
100 s Allan var. <2 × 10
−12
Warm-up interval 10 minutes to meet short-term
stability specification
Power consumption 70 W (at warm-up),
100/120/208/240 VAC,
50/60 Hz
Output 10 MHz, 1 Vpp sine wave
Prescaler
Frequency ratio 10:1
Input impedance 50 Ω
Max. input level +23 dBm
Input freq. range 50 MHz to 2.2 GHz
Input sensitivity See graph
Output
Output load 50 Ω
Output amplitude 700 mVpp square wave
Output offset 500 mV
General
Size 17" × 3" × 14.5" (WHD)
Weight 15 lbs.
Warranty One year parts and labor on defects
in materials and workmanship
SR625 Specifications
Stanford Research Systems phone: (408)744-9040
www.thinkSRS.com
Ordering Information
SR625 Frequency counter $14,850
(w/ Rb timebase and rack mount kit)
SR625 rear panel
20.000
10.000
Prescaler Sensitivity (Typical)
Maximum Amplitude
0.000
-10.000
-20.000
-30.000
Input Amplitude (dBm)
-40.000
1000 1200 1400 1600 1800 2000
Minimum Amplitude
Input Frequency (MHz)
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