[time-nuts] wtd: WWVB info

[Bob Camp]

Hi

10 MHz does not divide by an integer to 60 KHz. 15 MHz, 6 and 9 MHz are all more
reasonable candidates. The attractiveness of 15 MHz and the value of a tunable 
OCXO is what makes the current $25 price of the KS boxes pretty attractive. You
*might* even be able to dispense with the tear down of the KS box and feed it 1 pps out
of your ADC / FPGA / MCU / Bailing wire rig. Instant WWVB disciplined OCXO. 

Bob

> On Aug 5, 2015, at 6:07 PM, Mike Magin <mmagin at lowerarchy.com> wrote:
> 
> If one were trying to use it not simply for the time code but also as a
> frequency reference, it seems to me that the ideal thing would be a ADC
> that can easily use an external clock (derived from a local voltage-tuned
> OCXO reference under control of the SDR).  Otherwise one is doing (rather
> coarse) software compensation for the phase offset between the ADC clock
> and the WWVB signal.
> 
> Does that make sense?  Anyone know of some reasonably affordable
> off-the-shelf ADC board/module that takes 10 MHz external clock?
> 
> On Wed, Aug 05, 2015 at 12:40:10PM -0500, Graham / KE9H wrote:
>> There are several high end audio Analog to Digital Data converters that
>> will clock at 192 kHz, ~23 bits ENOB, which puts a 60 kHz signal sweetly in
>> the first Nyquist zone. Typical NF of the front end of the data converter
>> is 20 to 25 dB, so noise floor well below the atmospheric noise level at 60
>> kHz.  You would only need a preamp if you were running some negative gain
>> antenna.  Lots of dynamic range.  Won't overload until 2 Volts peak-to-peak
>> or so.  A very simple, high performance digital receiver front-end.
>> 
>> --- Graham / KE9H
>> 
>> ==
>> 
>> On Wed, Aug 5, 2015 at 6:15 AM, Bob Camp <kb8tq at n1k.org> wrote:
>> 
>>> Hi
>>> 
>>> The front end would be “dealers choice”. He who does the
>>> project gets to decide what gets used.
>>> 
>>> If you look over some other designs, you can indeed get
>>> a device going with a 12 bit converter. The qualifier is that
>>> the signal to noise needs to be pretty good. With fades
>>> and switcher interference, you probably would notice its
>>> limitations.
>>> 
>>> The “other end” of the design spectrum would be with a part
>>> designed as a high range font end chip. You can get to a lot
>>> of bits at low frequency. Even the prices aren’t all that crazy.
>>> 
>>> Is there one and only one approach here? Not in any way. There
>>> are several thousand possible ways to do it. AGC or no AGC would
>>> be a pretty major decision. Next decision would be things like clocks.
>>> 15 MHz from a ($25) KS box that also puts out 10 MHz looks like a
>>> pretty good choice at the moment.
>>> 
>>> Past that it’s decimators / filters and the usual DSP stuff (or any of
>>> a dozen alternatives). Given the high noise environment I’d lean towards
>>> a DSP approach.
>>> 
>>> Most of the choices run into the easy / quick / cheap tradeoff triangle.
>>> I’m
>>> sure that the debating process can find a solution that should “cost 10
>>> cents”. I’m
>>> also sure that a basement lash up of available parts is quick, but hard to
>>> reproduce.
>>> I’m not terribly surprised at the lack of 10 cent solutions. I’m a bit
>>> surprised
>>> that there are no unique lash up designs. The debate process seems to
>>> have made this a pretty un-attractive thing to do.
>>> 
>>> Bob
>>> 
>>>> On Aug 4, 2015, at 11:36 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
>>>> 
>>>> 
>>>> kb8tq at n1k.org said:
>>>>> So far there have not been any home brew design radios show up that will
>>>>> demodulate and lock to the new data format. There is plenty of info on
>>> the
>>>>> transmit format. The demodulation approach is not crazy hard. That said,
>>>>> there’s still a lot of work to get a receiver running.
>>>> 
>>>> Has anybody looked into a software approach?  What sort of front end
>>> would
>>>> you want?
>>>> 
>>>> 
>>>> --
>>>> These are my opinions.  I hate spam.
>>>> 
>>>> 
>>>> 
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