Key Features

• Accuracy better than 10-12 during entire life
• Long life 10 years cesium tube
• Extremely compact size 3U high (5.24’’ x 8”x 19”rackmount)
• Front or Rear access connectors (depending on configuration)
• Single 10 MHz output
• Programmable 1 / 5 / 10 MHz TTL output
• Redundant DC power supply inputs
• Remote control and monitoring via RS232

Dealing with propagation delay in precise timing systems

One of the inevitable problems in distributing precise time in systems is dealing with propagation delay of signals through cabling. In a typical coaxial cable, signals propagate at 70% of the speed of light. In rough terms this means that it takes approximately 1ns for a signal to  travel over 1ft of coaxial cable. Most GPS timing receivers allow for a simple compensation for the antenna cable delay. However, this does not fully address the problem, since in many cases the timing synchronization has to be further distributed from the GPS timing receiver to multiple users either within a campus facility through a distribution amplifier, or even within an equipment rack. For a typical system that has a synchronizing source such as a GPS receiver at the top of a rack cabinet feeding a series of rack mounted chassis through intra-rack cabling, the delay in receiving the synchronization (typically 1pulse/sec) will be 12ns to a chassis mounted at the bottom of the rack, and 5ns to an adjacent chassis, when typical 38” cable feeds needed to slide equipment shelves out of the rack are considered. If multiple equipment racks are involved, the skew due to cable propagation delay can be even larger. These delays can lead to significant synchronization biases in the operation of high accuracy systems. In a campus-wide system, where hundreds of feet of cable may be needed, much larger differential delays can result in skews of hundreds of nanoseconds. Brandywine has addressed this problem in their NFS220 Time and Frequency Standard and the FTSU100D Distribution Amplifier. In both products a web page control allows the user to add or subtract delays in each individual 1PPS output so that intra-rack propagation delays can be dialed out, ensuring that 1PPS synchronizing signals arrive at their destinations simultaneously.