[time-nuts] new WWVB BPSK dev board

[Alex Pummer]

There is a problem with most pre-amplifiers and also particularly with 
anything up font of the sampling; to get  good data the amplitude of the 
sampled signal has to have relative high levels, comparable to 
microphone output level -- up to 50mV -- if one wanted to use the sound 
cart input. Additionally to that the sound card has it's internal 
amplifier before the A to D converter. Unfortunately the "vicinity" of 
the 60kHz is not a quite area, but it is full with noise of house hold 
and industrial origin. I spent substantial time to investigate that 
noises and I found many unsuspected sources. I may own household I have 
on tooth cleaning jet for every day use, which was replaced recently wit 
a new one since the previous one was more than fifteen years old and 
started to show old age problems. The new unit looking from the outside 
was very similar to the old one except that the old had one AC motor the 
new one has a DC motor with a switching mode power supply, which is with 
the motor's commutator generating RF noise up to the TV bands disturbing 
the reception and of course generating enough interference to overload 
any sound card with pre -amplifier. I am very curious how did they get 
that device -- the water jet-- trough the FCC test  or did not ever 
border to do it? But that water jet  is not alone, just look your own 
computer's including it's power supply. You no not need any very 
sophisticated instrument just some old spectrum analyzer, which is 
running on it's own without any computer connection, and you will what 
is out there, sweep so between 35kHz to 100kHz use one coils as antenna 
with a diameter of 2' to 3' and at least thirty turns. With that set up 
you will be able to see WWVB to. If you turn the coil's axis 
perpendicular to the direction from your position to Forth Collins in 
Colorado, you will see the --AM also-- modulated WWVB at 60kHz. These 
illegal carriers with very large amplitude are able to overload the 
input of the sound card's -- or any other --A to D converter. The old 
WWVB receivers for the at the time just AM modulated signal used to use 
crystal filter for good reason, which is not usable any more since the 
frequency spreading of the phase modulation will not fit into the 
crystal filter's band width, and the settling time of the filter's 
output will cause one additional AM modulation.   By using some 
selection and very linear amplification I was able to get did I get a 
120mVp_p signal from WWVB and compared it's phase stability  to the 
phase of one other 60kHz signal derived from a GPS receiver with one 
u-blox board. If there is interest  I could describe how did I do it.

73

KJ6UHN

Alex

On 12/4/2018 8:09 PM, David G. McGaw wrote:
> Actually, an RTL-SDR can because there is direct access to the ADC
> available by soldering to internal pads:
> www.rtl-sdr.com/rtl-sdr-direct-sampling-mode/  That will give you 8-bit,
> 14.4Msps.
>
> But as has also been said, a good sound card sampling 24 bits at 192kHz
> can be used.
>
> David N1HAC
>
>
> On 12/4/18 6:54 PM, Poul-Henning Kamp wrote:
>> --------
>> In message <2e7cf0ff-4094-2750-4874-96dfe2efe485 at earthlink.net>, jimlux writes:
>>
>>> I'm going to bet that the 8 bit RTL-SDR isn't going to work on 60kHz.
>> I don't know about the RTL-SDR, but 8 bits will get you quite far with
>> slow moving time signals like WWVB because you can average for minutes
>> if you want - provided you feed the ADC a good stable clock.
>>
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