[time-nuts] WWV/CHU

[Bob kb8tq]

Hi

There are a *lot* of HF receiver gizmos out there these days. Is $5 to much to spend? 
Does the budget make it up to $300? Do you want to pick up *every* time transmission
at once? (as constrained by propagation). 

For something like 5 MHz / 10 MHz WWVB plus CHU, there are $20 demo boards that look like
they would do the trick as.a direct sampling device. I haven’t tried one yet. I have no idea
how well they actually do. 

My guess is that at HF, propagation will limit the usefulness of the carrier as a stable 
signal. Anything that will drift less than a few 10’s of Hz is going to do fine to pick up the audio.
That’s not all that crazy hard at 10 MHz. 

Once you do get the time ticks off of the audio, you still have a “millisecond” level accuracy
signal due to propagation. You also have a signal that will drop out from time to time ( unless
you live in Colorado).

Bob


> On Mar 29, 2018, at 10:08 AM, jimlux <jimlux at earthlink.net> wrote:
> 
> On 3/29/18 3:49 AM, Attila Kinali wrote:
>> On Thu, 29 Mar 2018 03:12:24 -0700
>> Hal Murray <hmurray at megapathdsl.net> wrote:
>>> What do I need in in order to get time from WWV or CHU?
>>> 
>>> Do I need a fancy receiver as a front end?  Do I have a chance with one of
>>> the low cost USB thumb drive size receivers?
>>> 
>>> Is there an obvious software package to start with?  (Linux)
>> I think the easiest is GnuRadio... A quick googling lead
>> to https://github.com/jasonabele/gr-wwvb
>> I don't know anything about it so use at own risk :)
>> But at least it seems like something that can be done easily
>> on a rainy evening.
>> Normal RTL-SDR's do not work for WWVB as they have a lower cut of
>> frequency in the range of 20-50MHz...unless you bypass the tuner
>> chip and feed the signal directly to the ADC. As IIRC all RTL-SDR
>> give you something like 2Msps, that should be more than plenty to
>> decode WWVB and related signals. If you feed the RTL-SDR from an
>> external frequency source, you should be able to related that
>> frequency source to WWV.
> 
> The RTL-SDR is an interesting device - I'm putting together a hobby HF interferometer with GPS to provide time tags.
> 
> Yes, most of the newer parts (RTL-SDR v3, for instance) provide a programmable bypass of the front end downconverter (the part is actually designed to tune TV signals and the L-band output of a consumer dish LNB)
> The backend chip (RTL2832U) is a digital downconverter which mixes and filters the nominal 3.5 MHz IF which is sampled at 28.8 MHz
> 
> You can actually adjust the output sample rate - something around 2 Msample/second is the default, but there's lots of other rates available.  For WWV you could crank it down, but..
> The ADC is 8 bits (7 ENOB) and the output is 8 bit I/8 bit Q.
> 
> Folks have modified the RTL-SDR to accept an external frequency reference, so you could take the output from your ensemble of Cesium references to discipline a hydrogen maser (so your close in phase noise is better),then use that to drive a 28.8 MHz discrete divide/multiply chain, and run that into your $30 receiver to improve the frequency accuracy.  (not for nothing are we called time-nuts)
> 
> 
> 
> 
>> 			Attila Kinali
> 
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