[time-nuts] simple phase finder

[Bob kb8tq]

Hi

One of the most common things to do for an antenna is to come up with a resonant 
loop. That gives you *some* rejection of the massive 60 KHz switcher noise you have
to deal with. By fiddling a bit with the turns and pickoff, you can come up with a 
high Z output (if you like JFET front ends) or a low Z (if you like common base setups). 
Interesting features like balanced feed to reduce pickup are also fairly simple. 

An E-Field probe is another way to get the signal in and it can have some advantages in 
the right setting. If you are after broadband coverage, they certainly are a better bet than 
a resonant loop. 

A while back a list member was making 60KHz antennas and selling them on eBay. It’s 
been a while since I went looking for them. They may still be out there. 

With loops (provided your home isn’t the source of the 60KHz trash) a fairly good signal 
can be had with an indoor antenna. With the probe antennas, you really need to get out
and away from “stuff” to get a reasonable signal. Having a resonant loop in a heated 
space helps reduce the phase issues of a high(ish) Q device and day/night swings. 

I have seen a lot of radios over the years that claim sub-500KHz coverage. Many of them
have been so deaf down there as to be completely useless. The signals are fairly strong,
but indeed the radios have been very deaf …. It’s not just about the antenna. 

Bob

> On Dec 5, 2018, at 9:51 AM, jimlux <jimlux at earthlink.net> wrote:
> 
> 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.
> 
> 
> 
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