Hi The issue is dithering the input to the ADC. If you filter "to much" you get to the point that you are not dithering very much. That actually reduces the linearity of many ADC's (ie spurs go up). It very much impacts your ability to pull out low level signals.
Done that? yes lots of times. Got it working? yup. It's a very standard text book approach that's been around for many decades. Can you carry dithering too far? Indeed you can. You do not want to overload the ADC. Once it's clipping, you aren't getting anything useful out of it. Things like broadcast AM and switching power supplies are both threats to your receiver. If your loop antenna has a Q of 100 or so, it's going to have a bandwidth of about 600 Hz. That eliminates the AM band pretty well. Switchers can be anywhere, yes you might have one at exactly 60.0001 KHz. Call up Javad for a brick wall filter in that case. Your 600 Hz wide antenna has taken out a lot of noise. More than likely, your ADC isn't getting much into it. A 6KHz wide antenna would still kill the AM band. The lower Q antenna also may give you less trouble over temperature. Where between Q=10 and Q=100 you get reasonable dithering *and* nuke your local crud *and* get a reasonably stable system.... TBD. Bob -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of J. Forster Sent: Wednesday, September 26, 2012 9:18 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] WWVB PM Receiver Have you actually tried it and gotten it working, except possibly in a very strong signal area? -John ================ > Hi, > > From: "Bob Camp" <[email protected]> > >> A tuned antenna probably is going to provide all the selectivity you'd >> need. > Another possibility is to modify your old circuit like that: > http://www.maxmcarter.com/rubidium/2012_mod/index.html > > Bye, > Jean-Louis > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
