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

gary lists at lazygranch.com
Sat Mar 17 14:17:35 UTC 2012


I think the tempco of the ferrite is more significant than drift in the 
analog filter. Of course this again implies the better design is to not 
load the inductor with a cap, i.e. stay broadband, and then just filter 
post the preamp.

The open circuit voltage will be lower without the resonant circuit. 
This is a case where the BF862 might do some good since the goal is to 
not load the inductor, either resistively or with capacitance. When you 
are dealing with components that are around 1nV/sqrt(hz), you can afford 
to throw some circuitry at the problem especially since the atmospheric 
noise will dominate.



On 3/17/2012 6:38 AM, Marek Peca wrote:
>> Any filter's group delay can be equalized by all pass filters.
>>
>> Delay builds up at the filter corner. Since everything in the real
>> world is causal, you add delay outside that corner frequency but in
>> the passband to equalize it. This is to say, you can't remove delay,
>> but just add it to flatten out the group delay.
>
> Yes, the compensation can be made and it has been also pointed out in
> the first comment by Poul-Henning.
>
> The only remaining question is, how stable are the analogue filter
> parameters over time, to be compensated by fixed digital filter. It
> seems to me, that some very small phase errors produced by such a
> filter-filter mismatch may be acceptable.
>
> At least for low-cost device which I would like to rebuild and offer for
> WWVB audience (which is not present in our land).
>
>
> Best regards,
> Marek
>
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