On 3/29/18 3:49 AM, Attila Kinali wrote:
On Thu, 29 Mar 2018 03:12:24 -0700
Hal Murray <[email protected]> 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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