The Well Tempered Master Clock - Building a low phase noise/jitter crystal oscillator

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#3,122
Supersurfer said:
This one seems to be a very good clock unit. Phase noise is even better than the 11mhz driscoll version.

They also mention that the best way to shield the clock from rfi is a steel enclosure not aluminium.

MUTEC - Professional A/V and High-End Equipment - REF10
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Steel is better imho around for PS and upper casing because field is "focusing" on it if Iunderstood correctly. around the clock unit, Mumetal or copper in that order of prefenrence are certainly way better than steel.Aluminium seems less good than the steel and need to be very thick 'several cm) to have a little interest.
In my dac I use steel wall / case to seperate the multiple power traffo (4) from the pcb. While around I think I will use some copper as casing under the wood. I didn't hear difference with and without the steel though... maybe it's better with measurment 🙄.


Are the low frequencies xtals proofer to vibration vs say 50k Xtals ?
 
#3,128
Markw4 said:
At RF copper can be reflective, such as in a resonant cavity box. Steel tends to be lossy.
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Useful tidbit of info, thanks. I use copper and brass shielding extensively around current clock and streamer chassis. No doubt better than nothing, but good to know for next time.
I plan to use the box Andrea has spec'd. If it is good enough to produce the graphs he has posted, I'm not sure its worth the effort to experiment. More than likely I'll end up dropping the whole thing into a wood box and fill it with sand, but that's just me. 🙂
 
#3,129
#3,130
The best low frequency shields are magnetic. Mumetal works well but needs to be annealed after fabrication. Steel also works if thick enough. I have seen references to 18 Gauge in the past but that's fuzzy memory. For high frequencies you need conduction. Silver plated copper or brass works very well if there are no holes or slots (sounds like PCB ground plane recommendations). Remember you are both keeping the noise out and the RF in. Use feedthrough caps to connect through the housing, the Wenzel connections shown below are a good example of RF safe connections. The feed through prevents much RF from getting in or out of the enclosure. And try to seal up seams with RF gaskets if you can. Its why the commercial OXCO's are sealed with solder.

I had a really exotic EMI test receiver for a while. The housing was constructed of steel, furnace brazed to seal off of the seams and then silver plated to maximize the shielding. Weighed a ton. It had continuous tuning from 100 KHz to 1.2 GHz so it would be sensitive to anything. Important when you are trying to make sure your secrets are safe from foreign powers.
 

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#3,135
andrea_mori said:
Oscillator type: Driscoll
Frequencies: 5.6448 MHz, 6.144 MHz, 11.2896 MHz, 12.288 MHz, 22.5792 MHz, 24.576 MHz
Output: sine wave (+16 dBm to +18 dBm)
Crystals: SC-Cut overtone only

Board size: 151mm x 75mm (excluding SMA connector)
Suitable box: Hammond 1455J1601 (Mouser part 546-1455J1601)

Board options: finished and semi-finished
Note: supplied without crystal and box
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Andrea, Can this cct be used with the 16.9344MHz crystal?
Thanks,
 
#3,138
Thanks, in another post I asked if these are good for the 16.9344MHz crystal? What value changes are required for the driscoll. I replied too fast as you already answered. Yes SC cut, do you have the value changes required?
 
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