Electronics > Projects, Designs, and Technical Stuff

3 Dollar Precision Frequency Standard

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Dago:
Good oscillators from a real distributor are also not that terribly expensive, like this +-0.28ppm 10 MHz oscillator http://www.digikey.com/product-detail/en/DV75C-010.0M/CW750CT-ND/3524566

MK:
The most stable quartz cuts with the best specs are usually around the 3-30MHz range, above that they are running at overtones usually, and below that they are getting quite large, and more microphonic.

paulie:
Due to some offline requests a diagram has been attached to first post:

paulie:
So one week after the first WWV "tune-up" I checked again and drift for the Ebay counter varied between 0-1 count (0.1ppm) and reference 1-2 counts (0.2ppm). Interestingly another club member brought in his rubidium based standard and it was 2-4 counts off over 10 minutes. IDK if this is normal for those or a defect but at 1% the cost these cheap oscillators seem to do very well by comparison. I may do another checkup in a month or two.

paulie:

--- Quote from: Mechatrommer on April 11, 2015, 03:43:31 pm ---btw, the $3 avr is outputting square wave right? not pure sine?
--- End quote ---

Yes, coming from AVR pin a VERY square wave. In fact because of Atmel output components sharper edges than you might see on any other MCU in its class. So lots of harmonics, probably way up into microwave region. As mentioned in the Ridgen Calbox blog this is good if you're doing things like calibrating scope probes, LA, etc.. Maybe not so great for distributing signals from GPSDO or Rubidium unit because in some few cases equipment being fed misbehaves w/o clean signals. Judging from that thread here asking about square vs sine not a big problem though.

Anyway in the process of playing around with transistor multiplier ckt like in the Calbox site and also a poor mans WWV receiver project I built several different 10mhz resonant LC circuits. My goal was to see how cheap one could get. I found by winding a few turns of thin wire around a paper form and tacking on a small ceramic total cost was possible under 10 cents. That includes using half an axial ferrite bead as tuning slug. I wondered what about hooking it up to output of the 10mhz frequency reference to suppress those nasty odd harmonics. Lo and behold, result was clean fundamental sine wave. At least as far as I could tell w/o a lab grade spectrum analyzer. Looks great on the scope and very little picked up on HF and VHF reciever.

For those who might be curious here's a pic.

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