[sdiy] ot: long wave radio reciever for time/frequency

[Tim Ressel]

Yo,

I once asked the Gods of RF at Agilent why they used
crystal ovens to derive accurate timebases and not
just pull down WWV and use that. The answer was: due
to atmospheric phenomina the carrier frequency of a
radio signal can have significant amounts of jitter
and drift. 

I'd still build it, tho'. Just for fun. 

--Tim

--- Czech Martin <Martin.Czech at Micronas.com> wrote:
> Just for fun I want to build a reciever for the
> 77.5kHz
> German time/frequency standard radio transmitter.
> Other countries have similar long wave frequencies.
> 
> I want to use a ferrite antenna.
> For now I have 100 + 100 windings of 0.2 mm copper
> wire,
> single layer. I want to see the difference between
> 100
> and 200 windings.
> 
> -would it be harmfull to have a second layer? i.e.
> 400 turns?
>  (I fear that winding capacitance might influence
>   the resonance I want to build at 77.5kHz)
> OTOH I want to have as much signal as possible.
> I have read that in Zurich (Switzerland) the signal
> can be as low as 100uV.
> 
> For the reciever I've found that external noise
> (athmospheric)
> will be much larger then any amplifier noise.
> So I could save here. Any opinions?
> 
> What do you think about the idea to divide the
> amplified signal
> by 77500 in order to have 1 Hz square pulses?
> I mean, the hope is that any noise will be averaged
> if I use
> ripple counters as much as possible (the
> factorisation
> is 2*2 * 5*5*5*5 * 31, why did they do that? 31,
> what an ugly prime, ...)
> So I hope that in spite of athmospheric noise the
> derived second will be quite exact, maybe in the
> same range
> as a quartz osc. would be.
> 
> ?
> 
> 
> I think that filtering the noise via pll would
> perhaps have more
> noise problems, (4046), unless I use an LC tank.
> 
> Since the antenna noise is so large, I could perhaps
> just use
> a cascade of cheap op amps, to have a gain of 1000
> or so.
> Any bandwidth limitation should not be necessary,
> and this would require LC filters (77.5kHz is hard
> to do
> with RC active filters and Q>5 or so.)
> 
> ?
> 
> 
> Cheers
> 
> Martin Czech
> 
> CAD/CAE Library Group
> Micronas GmbH
> Hans-Bunte-Str 19
> D 79108 Freiburg
> Tel.: +49-761-517-2422
> FAX.: +49-761-517-2258
> http://www.micronas.com
>  
> 


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