General Information vii
Interfaces
Front-panel LEDs Locked Indicates frequency is lock to
rubidium
Unlocked Indicates frequency is unlocked
1 pps input Blinks with each 1 pps reference
input applied to rear panel
1 pps sync Indicates 1 pps output is
synchronized within ±1µs of
1 pps input
Rear Panel (BNCs) Frequency Adjust 0 to 5 VDC adjusts frequency
by ±0.002 ppm
1 pps input 100 kΩinput. Requires CMOS
level pulses (0 to 5 VDC). If an
external 1 pps input is applied, lock
is maintained between the 1 pps
input and 1 pps output with computer
adjustable time constant from 8 minutes
to 18 hours.
1 pps output 50 Ωpulse output
10 MHz outputs Three 50 ohm isolated 10 MHz
sine outputs
SIM (DB–15/male) power and communications
Operating Temperature +10 ◦C to +40 ◦C
Temperature stability ∆f/f<±1×10−10
(+10 ◦C to +40 ◦C)
Storage temperature −55 ◦C to +85 ◦C
Magnetic field ∆f/f<±2×10−10 for 1 Gauss
field reversal
Relative humidity 95 % (non-condensing)
General Characteristics
Interface Serial (RS-232) through SIM interface
Power +24 VDC
Supply current 2.2 A at start-up,
0.6 A after warm-up period
Weight 5 lbs
Dimensions 1.500 W×3.600 H×7.000 D
SIM940 Rubidium Frequency Standard
