[time-nuts] WWVB PM Receiver

[J. Forster]

You have not answered my question. Yes or no, do you have it working on
the new WWVB format?

-John

=================


> 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: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] 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" <lists at rtty.us>
>>
>>> 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
>>
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>
>
>
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