Wednesday, March 21, 2012

Proposed OS Freq Standard

I have an idea for an Open Source Project, but first some background, . .


Dave Jones of EEVblog fame, is designing and building a very neat Open Source Power Supply, if you are not familiar with his project check it out at his Blog. His other blog enteries describe some of his design, process, and trade-offs. It is a very interesting project and I for one, will be ordering at least two when they are available.

If you are a reader of the blog, you will know that I have been experimenting with the Parallel Propeller Micro Processor (Prop) for use as a Amateur Radio Multi-Mode Beacon. The Propeller has within is the ability to generate RF square waves that I use to drive my Beacon. This Frequency can be set to any frequency from 500Hz to 120MHz. But there is a bit of a problem with the "stock" Propeller frequency synthesizer; it is not very stable or accurate. In my quest to solve this problem; Jeff - KO7M and I ( and with some help from some of my readers) hit upon the idea of using a TCVCXO for the system clock. Initial experiment suggest the Beacon frequency can be made to be very stable and accurate.

Last night at Jack - WA7KMR's Homebrew Meeting; we discussed Frequency Standards and the relative size, resolution and stability of some of the equipment that Jack had collected over the years. We also discussed feedback loops to increase accuracy and stability.

After getting home late, and after turning off the lights, my brain tuned on.

Most readers of this blog can always use more test equipment - right?. Therefore, . . .

My Proposal

An Inexpensive Open Source Variable Frequency Standard, based on the hardware design of Dave Jones's Power Supply; using the same case, battery pack, input voltage regulators, LCD display and push button layout. And using the TCVCXO and Propeller Micro Processor for control and function of the Frequency Standard.

  • Use the TCVCXO for the master clock of a Variable Frequency Standard
  • The Prop could select the source for the output, either a straight divide by N circuit, or an output from the Prop synthesizer.
  • The display could indicate the frequency and source.
  • A GPS input could be used to phase lock and adjust the already +/-2 ppm TCVCXO to much-much tighter tolerances. The Prop has these functions built-in.
  • The Prop would detect and display the TCVCXO and GPS phase error.
  • Feedback from the Prop to the TCVCXO (via filters filters) would adjust as TCVCXO as necessary.
  • The device would be small, battery powered and portable.
  • Multiple Frequencies can be produced simultaneously, on different output connectors.
  • And, relative inexpensive.

Jeff's and my initial work with the TCVCXO was with his Frequency Standard, but it only had a few decade switch selectable frequencies available, I think the Prop can provide much more flexibility.

I know there are many High Accuracy Time Standard hobbiest, and this would not qualify in that category. The expected Stability and Accuracy that can be expected is still debatable and untested, but I think the idea is worth pursuit for a bench source.

Dave Jones has done some great work; his generic input power supply and charging circuit, the case selection and layout, display and controls, are just begging for additional creative devices. I suspect his Open Source equipment form factor and layout will become a Standard, and it will become known as; The Platypus.

My Proposed Variable Frequency Standard would be an Open Source Project based on The Platypus.

Note: there are other similar projects on the web: Google, Open Source Frequency Generator

I am looking for feedback.

What say you?


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