[time-nuts] 60kHz Loop antenna
J. L. Trantham
jltran at att.net
Sun Oct 3 18:29:08 EDT 2010
I have been very superficially following this topic and looked at some links about 60 KHz Loop antennas, including one on Tom's site (I think?) describing building one out of 100 feet of RG58 coax.
Could CAT 5 cable be used? It is 4 twisted pairs and you can get it shielded. Any issue with 'twisted pairs'?
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of J. Forster
Sent: Sunday, October 03, 2010 1:48 PM
To: b Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] 60kHz Loop antenna
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:
> â€œTune 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
> 25 to 40. More will cause temperature and tuning problems, less will let
> in too
> much noise.â€
> To tell the truth, I really haven't given this much thought for the
> 30+ years my loop has been working.
> Â Â Â Â Â Â Â Â -Arthur
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