Using laser-sourced light beams rather than wireless RF to link spacecraft with Earth offers the possibility of a significant increase in data rates. Still, there are significant technical challenges to the concept. Scientists, engineers, and researchers communicating with spacecraft have a problem: there’s so much data coming from these spacecraft – and to send to […]
The PC-board atomic clock, Part 3: The CSAC cesium physics cell
Atomic clocks have shrunk from room-sized assemblies down to PC-board mountable modules, admittedly with lower performance than their big siblings but still far better than crystal-based timing alternatives. Every engineer knows that developing a viable design and product is not just a matter of theorizing a design, identifying the constituent components, or building a single […]
The PC-board atomic clock, Part 2: The CSAC design
Atomic clocks have shrunk from room-sized assemblies down to PC-board mountable modules, admittedly with lower performance than their big siblings but still far better than crystal-based timing alternatives. Engineering is largely about tradeoffs and constraints, and atomic clocks are no exception to this situation. As these clocks are being designed into smaller packages through innovations, […]
The PC-board atomic clock, Part 1: Primary and secondary standards
Atomic clocks have shrunk from room-sized assemblies to PC-board mountable modules, admittedly with lower performance than their big siblings but still far better than crystal-based timing alternatives. Atomic clocks are based on the transitions of energy states of specific elements such as cesium, ytterbium, rubidium, and others under specific and tightly controlled conditions. They are […]
An overview of filters and their parameters, Part 4: Time and phase issues
Understanding how filters are characterized is the first step in choosing an appropriate topology with suitable specifications. Thus far, we have focused on filters primarily in terms of their frequency response. However, it is equally legitimate to look at their time-domain and phase-related performance, and in many cases, just as or even more important. Q: […]
An overview of filters and their parameters, Part 3: Key parameters
Understanding how filters are characterized is the first step in choosing an appropriate topology with suitable specifications. This part looks at the basics of filter characterization and parameters. Q: What is an example of a very basic filter? A: The most common analog filter is the single-stage low-pass RC filter (Figure 1). It is often […]
An overview of filters and their parameters, Part 2: Basic Concepts
Understanding how filters are characterized is the first step in choosing an appropriate topology with suitable specifications. Filters are both a simple and also complicated and often confusing topic. This part clarifies some of the issues. Q: Why are so many discussions about filters so confusing? A: There are many reasons, but one is that […]
An overview of filters and their parameters, Part 1: Context
Understanding how filters are characterized is the first step in choosing an appropriate topology with suitable specifications. Mention “filters” to electrical engineers of the older persuasion, and you’ll likely see a look of nostalgia mixed with fear. Why so? Because “back in the day” a course on filter theory was mandatory for nearly all EE […]
Free-space optical links, Part 3: Standard units
Free-space optical links provide a reliable, cost-effective, and quick way to link two fixed communication nodes located a few kilometers apart. The previous part of this article looked at real-world issues that make a practical FSO link a design challenge. This part looks at a family of commercially available FSO systems. Q: Can you build […]
Free-space optical links, Part 2: Technical issues
Free-space optical links provide a reliable, cost-effective, and quick way to link two fixed communication nodes located a few kilometers apart. The first part of this article established the basic operating principles and rationale for free-space optical links. This part looks at some practical issues associated with their implementation. Q: How do you aim the […]
