[time-nuts] 60kHz Loop antenna

J. Forster jfor at quik.com
Sun Oct 3 14:47:32 EDT 2010

I observed a diurnal phase shift with my 117A system. I never investigated
whether this was due to loop phase shifts with temperature or propagation,
but it was likely a combination.

These phase shifts matter less if you are doing long term (multi-day)
measurements, but, to be valid, your system has to maintain phase lock for
the entire time. In my experience, that rarely happens in my location.
Remember a 1 cycle hop is about 16-17 usecond.

Phase shilt with temperature becomes a real worry if you are trying to
adjust a local standard in a few hours or a day.




> John,-"My concern with tuning the loop is that as the tuned circuit drifts
> with
> temperature, or other things, an extraneous phase shift will be intoduced
> to the received signal. Remember, the phase of a complex pole pair tuned
> circuit goes from +90 to -90 degrees as you sweepo through resonance. The
> higher the Q, the steeper this effect would be."
> +++++++++++++++++
> Don Lancaster addresses this concern in his article where he states:
> “Tune
> this coil to 60 kHz with high quality polystyrene capacitors or the more
> expensive
> silver micas. Any other capacitor type is unsuitable. The coil Q should be
> around
> 25 to 40. More will cause temperature and tuning problems, less will let
> in too
> much noise.”
> To tell the truth, I really haven't given this much thought for the 30+
> years my loop
> has been working.
>          -Arthur
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