SR625
Frequency Counter with Rb Timebase
  • 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 Front Panel
SR625 Rear Panel
Features

The SR625 Frequency Counter is a NIST traceable frequency counting standard for calibarating 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 stablity (<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 stablized 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.
 
Specification
The SR625 combines a SR620 Time Interval/Frequency Counter with a rubidium timebase and a fast 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 variance <1 ´ 10 -11
     100 s Allan variance <2 ´ 10 -12
Warmup interval 10 minutes to meet short-term stability specification
Power consumption 70 W (at warmup), 100/120/208/240 VAC, 50/60 Hz
Output 10 MHz, 1 Vpp sine wave
Prescaler
Frequency ratio 10:1
Input impedance 50 W
Max. input level +23 dBm
Input freq. range 50 MHz to 2.2 GHz
Output
     Output load 50 W
     Output amplitude 700 mVpp square wave
     Output offset 500 mV
General
Size 17" ´ 3" ´ 14.5" (WHL)
Weight 15 lbs.
Warranty One year parts and labor on defects in materials and workmanship