[time-nuts] WWVB Dephaser Question

Fri Oct 9 23:12:06 UTC 2020

Hi

I don’t believe that the WWVB transmitters change power day
to night. Both the north and south antenna’s are fed with the same
power, regardless of the time of day…..

Bob

> On Oct 9, 2020, at 5:59 PM, rcbuck at atcelectronics.com wrote:
> 
> Paul,
> I was seeing a -10 dBm on the SA when they enter high power mode at
> night. At low power they are only a couple of dB above the nearby noise
> makers. But that is at the output of the last stage of my receiver. The
> WWVB signal was about 10-15 dB above the noise makers in my work shop. I
> don't know what the actual WWVB signal level is and have no way to
> measure it. I estimate the ferrite antenna to be approx 20k ohm which
> doesn't match the 50 ohm input of the SA. Maybe feed the rod antenna
> into a single stage op amp with a gain of 1 to feed the SA would work
> give me a rough idea?? I previously said I had 1 mV of daytime signal
> according to the WWVB maps. But that was wrong. In my mind I was
> thinking 1000 uV when the maps show the 100 uV coverage area. So receive
> level during the day should be around 0.1 mV. I have PCB's on order that
> hopefully will improve the receiver performance.
> 
> Bob,
> I'm still trying to figure out if a software or hardware solution is
> better. I've looked at the Costas loop and a PLL angle. But I run into
> the problem of the LO being on the same frequency as WWVB. Plus as Paul
> said the math is intimidating to me. Locking WWVB to a HF oscillator and
> dividing down to 10 kHz or so for the control voltage and I/Q
> demodulation may be an answer but involves more hardware.
> 
> For a software solution I don't know exactly how to approach the task. I
> don't have any DSP software experience so that option is out. I haven't
> made a decision on the CPU yet. I will just use whatever it takes for
> the job, probably a STM32 part of some sort. I have a couple of STM32
> development boards I can use when I get to that point.
> 
> Ray
> 
> 
> -------- Original Message --------
> Subject: Re: [time-nuts] WWVB Dephaser Question
> From: Bob kb8tq <kb8tq at n1k.org>
> Date: Fri, October 09, 2020 12:23 pm
> To: Discussion of precise time and frequency measurement
> <time-nuts at lists.febo.com>
> 
> Hi
> 
> Since you need a MCU to decode the data, you might as well get
> things in there sooner rather than later. There are a number of MCU’s
> out there that have fast enough ADC’s to do the job. They do have
> limited
> dynamic range. You can go to one of the 24 bit converters and have 
> a ton of dynamic range. It’s all up to you.
> 
> Once it’s into the MCU, it’s just code :). Depending on how much cpu
> 
> horsepower you have (and how much code you want to write) you can
> go more or less crazy …. PHK has some interesting tidbits on his web 
> site. http://phk.freebsd.dk/AducLoran/AducLoran-0.0.pdf
> <http://phk.freebsd.dk/AducLoran/AducLoran-0.0.pdf>
> 
> Bob
> 
> 
>> On Oct 9, 2020, at 1:38 PM, rcbuck at atcelectronics.com wrote:
>> 
>> Paul, Bob,
>> 
>> I am not using any commercial receiver. I am building everything from
>> scratch. The RF front end starts with a ferrite rod antenna feeding a
>> differential first op amp followed by 5 stages of op amp filtering and
>> amplification. When the last stage is fed to my spectrum analyzer
>> (through attenuators) the WWVB signal is clearly visible. I'm now trying
>> to figure out how to detect the phase shift so I can get the time data
>> for my CPU to process and send to a display.
>> 
>> I already have a GPS based clock that I built so I thought the WWVB
>> phase clock would be an interesting project.
>> 
>> Ray
>> 
>> -------- Original Message --------
>> Subject: Re: [time-nuts] WWVB Dephaser Question
>> From: Bob kb8tq <kb8tq at n1k.org>
>> Date: Fri, October 09, 2020 7:35 am
>> To: Discussion of precise time and frequency measurement
>> <time-nuts at lists.febo.com>
>> 
>> Hi
>> 
>> At least to me, anything dimensioned in the 100’s of feet is
>> “massive” compared to
>> the rod antennas normally seen in WWVB use ….
>> 
>> The other point being that if the antenna is some sort of large loop,
>> it’s going to be
>> a good long ways away from the receiver. You get both a larger signal
>> voltage and better
>> isolation …..
>> 
>> Bob
>> 
>>> On Oct 8, 2020, at 11:30 PM, John C. Westmoreland, P.E. <john at westmorelandengineering.com> wrote:
>>> 
>>> Hello All,
>>> 
>>> Are there any design details someplace regarding these massive antennas?
>>> 
>>> Thanks,
>>> John
>>> AJ6BC
>>> 
>>> 
>>> On Thu, Oct 8, 2020, 19:27 paul swed <paulswedb at gmail.com> wrote:
>>> 
>>>> Hello to the group.
>>>> Ray as Bob mentions you are taking a 10s of uv signal to a logic level of
>>>> maybe 4V.
>>>> If the loop is any place close to the divided down signal, it will
>>>> oscillate. It would take incredible shielding to protect the receiver.
>>>> Thats why you often see a solution that doubles to 120 KHz and modifies the
>>>> detectors to work at that frequency. That means hacking the radio
>>>> internally. Not fun. The other really annoy effect is that the doubling
>>>> slips phace due to noise and propagation. So if charting suddenly you get a
>>>> 180 degree flip. Thats messy.
>>>> The doubling solution can work. Search for carter and there are several
>>>> others.
>>>> But having tested and used all of the alternates and lots more on the east
>>>> coast decided they were too much trouble. You should see the box of boards
>>>> I have chuckle.
>>>> For me I am very happy with the d-psk-r. Though in being above board I
>>>> designed version 1 and Rodger and I did version 2. Its solid and no mods to
>>>> any receiver. Everything has always been released to the time-nuts group.
>>>> As they say have fun.
>>>> Regards
>>>> Paul.
>>>> WB8TSL
>>>> 
>>>> On Thu, Oct 8, 2020 at 5:39 PM <rcbuck at atcelectronics.com> wrote:
>>>> 
>>>>> Bob,
>>>>> 
>>>>> I am using a ferrite rod antenna for the receiver. No outside antenna.
>>>>> 
>>>>> Ray
>>>>> 
>>>>> -------- Original Message --------
>>>>> Subject: Re: [time-nuts] WWVB Dephaser Question
>>>>> From: Bob kb8tq <kb8tq at n1k.org>
>>>>> Date: Thu, October 08, 2020 12:40 pm
>>>>> To: Discussion of precise time and frequency measurement
>>>>> <time-nuts at lists.febo.com>
>>>>> 
>>>>> Hi
>>>>> 
>>>>> A lot depends on your antenna setup. You can also swamp out the incoming
>>>>> WWVB signal…….
>>>>> 
>>>>> Bob
>>>>> 
>>>>>> On Oct 8, 2020, at 2:07 PM, <rcbuck at atcelectronics.com> <
>>>>> rcbuck at atcelectronics.com> wrote:
>>>>>> 
>>>>>> I have read several different articles where the WWVB phase shift is
>>>>>> eliminated by doubling the signal to 120 kHz. Several members of the
>>>>>> list have built these units.
>>>>>> 
>>>>>> Assume I build a circuit to double the incoming signal and use a
>>>> schmitt
>>>>>> trigger to get a 120 kHz square wave. If I then divide that signal back
>>>>>> down to 60 kHz will that signal be strong enough to swamp out the WWVB
>>>>>> signal? I'm guessing it will be since it is at the 5 volt level and
>>>>>> somewhere in the +25 dBm or greater range.
>>>>>> 
>>>>>> Ray,
>>>>>> AB7HE
>>>>>> 
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>>>>> 
>>>>> 
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