[time-nuts] 60kHz Loop antenna
jfor at quik.com
Sun Oct 3 22:47:44 UTC 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.
> 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'?
> -----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.
>> 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:
>> Ã¢â¬ÅTune 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
>> 25 to 40. More will cause temperature and tuning problems, less will let
>> in too
>> much noise.Ã¢â¬Â
>> To tell the truth, I really haven't given this much thought for the
>> 30+ years my loop has been working.
>> Ã Ã Ã Ã Ã Ã Ã Ã -Arthur
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