[time-nuts] WWVB BPSK Receiver Project?
Marek Peca
marek at duch.cz
Wed Mar 14 22:51:56 UTC 2012
I will share my few bits of worked experience. But it may seem obvious.
> I'd say to go "100% SDR". In other words a simple front and that
> pushes as much of the functionality into software as possible. The
> carrier is only 60K. That is low enough that one can directly
> digitize the RF using an ADC that samples at only 192K/sec.
Not necesarilly. I received 77.5kHz very well in first sampling mirror,
sampling using ADS7813 16bit ADC @44ksps, yielding carrier at 10.5kHz in
discrete-time domain.
> 192K/Sec is a common sample rte for high-end audio and you can buy a
> 24-bit dual channel interface for under $200.
Beware, there are lots of sigma-delta ADCs for this purpose and I am in
doubt whether they could perform better than less-bits SAR ADC.
> So I'd use an antenna (the best would be a shielded loop with many
> turns of wire but ferrite "loop stick" could work) Follow that be an
> RF amp and very narrow filter and then the above 24-bit 192K ADC.
I must object a little bit against "RF" and "very narrow" -- I have used
very sloooooooow amplifiers (they were in a shack, original purpose DC
measurement up to some 100s of kHz) and nothing narrow (or even tuned) --
except the ferrite rod itself. The rest were 2 ICs (amp & ADC) and simple
RC network.
Worked very well, including few centimeters from laptop's CCFL inverter.
Best regards,
Marek
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