[time-nuts] 60kHz Loop antenna

J. Forster jfor at quik.com
Sun Oct 3 18:47:44 EDT 2010


I'd think the capacitance of the coax would present problems.

Before I got the cannonical antenna for my Austron LORAN Rx, I used a
roughly 30" square of 3/4" Cu tubing threaded with a bunch of #18
insulated hookup wire. The slick glop electricians use helped a lot. What
a mess though.

-John

===============

> 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'?
>
> Joe
>
> -----Original Message-----
> 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.
>
> FWIW,
>
> -John
>
> ================
>
>
>> 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.
>>
>> Â Â Â Â Â Â Â Â  -Arthur
>>
>>
>>
>>
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>
>
>
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