[time-nuts] simple phase finder

[jimlux]

On 12/5/18 6:32 AM, Bob kb8tq wrote:
> Hi
> 
>> On Dec 5, 2018, at 8:45 AM, jimlux <jimlux at earthlink.net> wrote:
>>
>> On 12/5/18 5:39 AM, Poul-Henning Kamp wrote:
>>> --------
>>> In message <4a8ff8d6-70b2-782e-cb79-21c7e9a49649 at earthlink.net>, jimlux writes:
>>>> If I were decoding WWVB to start, I'd break my samples up into 0.1
>>>> second or 0.5 second chunks and process them to see what the carrier
>>>> phase is.
>>> With stable signals like this, it is a bad idea to chop them up,
>>> in particular if your ADC runs from a good stable frequency.
>>
>> True enough - this was just to get started.
>>
>>> Instead continuously average the square of the signal into a 1
>>> second long circular buffer.
>>> Then multiply/sum that buffer with a 120kHz sine and cosine to find
>>> the phase angle.
>>
>> yes.. assuming your ADC is running off a sufficiently stable source.  I was thinking about a very low cost implementation where the ADC is running off a not very wonderful microcontroller clock.
>>
>>
>>
> 
> A stable clock probably is a pretty good bet on a “Time Nut” grade design. Indeed one objective might be to ultimately
> read out the phase directly WRT that reference . Some sort of PPS tick likely would get into all this as well.
> 
> 


I was thinking more about "can you receive it with a SDR implementation 
for <$50 and minimal heating of the soldering iron" without worrying too 
much about measuring small phase shifts.

Once you've got to that - then you've got a basis for further improvements.

I'll try the RTL-SDR with a non-active antenna on Friday and see what I 
can see here in Southern California.  I know my old style "atomic" clock 
does see the signal sometimes, so I can grab some sample when the clock 
says it's live.


If anyone has a suggestion for an off the shelf active antenna that's 
orderable and receivable by Friday, I'd love to hear it.  There's 3 or 4 
of them I've seen (Clifford labs, DX Engineering has one, I'm sure MFJ 
has one)

Why available by Friday? I'm going to be really busy starting next week 
for a month commissioning a satellite launching next week, so this 
weekend is my last opportunity to fool with actual technology.