[time-nuts] WWVB BPSK Receiver Project? (fwd)

[gary]

Which basically matched my assumption. If the inductor is loaded, you 
have a narrowband filter. So again, this does not imply that a ferrite 
rod antenna per se has phase distortion. It is the LC filter than 
effects the group delay.


On 3/17/2012 6:19 AM, Marek Peca wrote:
> Hello, gary,
>
>> I lost track of who wrote this, but why is it assume a ferrite rod has
>> non-linear phase. [Group delay error I presume). Now I assume this
>> presumes the rod is used in a LC circuit, but if the Q is not high,
>> the phase linearity won't necessarily be bad.
>>
>> Basically I'd like to hear more from whomever wrote this.
>
> It was me, a time-nuts newbie. My previous related posts were:
> http://www.febo.com/pipermail/time-nuts/2012-March/065049.html
> http://www.febo.com/pipermail/time-nuts/2012-March/065003.html
> http://www.febo.com/pipermail/time-nuts/2012-March/065009.html
> etc.
> and
> http://www.febo.com/pipermail/time-nuts/2012-March/065135.html
>
>> "The useful bandwidth of LF to HF radio is about 9kHz, DCF77-like
>> standards with PRBS is about 1.5kHz. Of course the ferrite rod as an
>> input filter *will* have a non-linear phase, but it still seems to me
>> it is the simplest and most common receiptor for LF time signals."
>
>
> Let me clarify the unclear statement. I was reacting to Poul-Henning
> Kamp's (true) statement, that: "The reason I use 1MSPS is that it allows
> me to use a very sloppy low-pass filter filter which just cuts off
> somewhere around 150-200 kHz, and do everything else in software. This
> means that I have no phase/group-delay distortion in the analog part
> that I need to compensate in software."
>
> In my design, I have used a ferrite rod LC circuit as and antenna and
> also the only element of selectivity in front of sampling. So, there was
> a 2nd order only filter.
>
> The useful signal of DCF77 (afaik yout WWVB is very similar now with
> BPSK) spans over ~1kHz. In my design, in contrast to P.-H. K.'s
> approach, I use only ~40ksps, so the 2nd order ferrite rod circuit
> should pass 1kHz, but it should attenuate somewhere around +-10..20kHz.
>
> I.e., the result will be always a compromise. Unfortunately, I don't
> have a measurement of my worked circuit's Q, but let us assume Q=20..100
> can be realistic value for ferrite rods. Then, the filter's BW will be
> somewhere 0.8..4kHz, what means, that its phase over the interesting
> 1kHz band will _not_ be straight line, but somewhat curved.
>
> This is the only thing about ferrite rod and phase I meant.
>
> To conclude, I would like to repeat, that in my oppinion the ferrite rod
> is easy and common antenna for LF signals, so that in such a case the
> phase will be curved anyway. Of course you can feed the P.-H. K.'s 1Msps
> input by more wide-band antenna, not the ferrite rod, to get more linear
> phase without SW compensation.
>
>
> Greeting from Marek
>
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