frequency reference

2 Articles

Hacking A Telecoms Frequency Standard For Your Lab

July 23, 2015 by 18 Comments

[Shane Burrell] came across a Nortel GPSTM and re-purposed it as a 10MHz reference for his lab. The GPSTM is designed to slot into a backplane, most likely for telecoms applications. So [Shane] needed to hack the board to run from a 48v PSU. Once powered up, it was relatively easy to interface as the card appears to contain the well known Trimble Thunderbolt module and is compatible with its software.

We’ve covered frequency references before and they can be a valuable addition to a lab. On the back of most scopes, spectrum analyzers and function generators you’ll find a 10MHz reference input allowing the user to supply a reference more accurate than that generated internally. Not only is an external reference often more accurate, it also allows you to keep all your equipment in sync with a common reference, which can be particularly important in some measurements. While some hackers opt for Rubidium sources, the GPS disciplined temperature-controlled oscillator in the Nortel unit should provide a nice stable reference.

A word of warning to [Shane] though, get sucked into hacking frequency references and you may become a time nut finding yourself climbing mountains to test the theory of relativity.

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The internals of a home built 10 MHz frequency reference.

Low Cost Lab Frequency Reference

September 15, 2014 by 16 Comments

[Mark] wanted an accurate frequency reference for his electronics lab. He specified some requirements for the project, including portability, ability to work inside a building, and low cost. That ruled out GPS, cesium standard clocks, rubidium standard clocks, and left him looking for a low cost Oven Controlled Crystal Oscillator (OCXO).

The Low Cost 10 MHz Frequency Reference is based around a Morion OCXO. These Russian oscillators are available from eBay second hand at about $40 a pop. With a stability well within the requirements, [Mark] order a few.

The next step was to stick all the components in a box. The two OCXOs in the box need about 3 amps to heat up, which is provided by a 12 V PSU. For portability, a sealed lead acid battery was added. The front panel shows the supply voltages, switches between mains and battery supplies, and provides connectivity to the OCXOs.

Since OCXOs work by heating a crystal to a specific temperature, they can use quite a bit of power in the heating element. To increase battery life, a neoprene foam insulator was wrapped around the OCXOs.

For less than $100, this portable tool will aid in calibrating equipment or creating very accurate clocks.