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Methods for improving 60kHz RF signal (WWVB)?

Started by Frnak McKenney March 13, 2014
On Tue, 18 Mar 2014 15:08:41 -0700, Jeff Liebermann <jeffl@cruzio.com> wrote:
> On Tue, 18 Mar 2014 11:51:15 -0500, Frnak McKenney ><frnak@far.from.the.madding.crowd.com> wrote: > >>> Nice. I have a GC-1000 Most Accurate Clock that I'm slowly >>> rebuilding. The original builder was seriously lacking in mechanical >>> ability and made a nice mess. >> >>Ouch! again. Did you get a manual with it? ( Hm. I'd better make >>sure I can locate _mine_ before I make any offers. <grin!> ) > > Thanks, but I have both the printed and scanned manuals. What I lack > is time and incentive.
Understood. [...]
>>Thanks. I've been looking at USB audio interfaces that would (a) work >>with Ubuntu Linux and (b) sample at greater than 2x60kHz, and while >>there are a lot of inexpensive ones out there, it's really hard to >>tell what their spec's are. > > There are quite a few that offer 192KHz sampling rate. The problem is > that the audio sections usually roll off at about 20KHz. I've found > cards that will allegedly go to 90KHz, but they're expe$ive. For > example: ><http://www.asus.com/Sound_Cards_and_DigitaltoAnalog_Converters/Xonar_Essence_STX/#specifications> > I have yet to find a USB version that does above 20KHz, but suspect > that once can be found which might be modified. (Yet another > project).
Nice specs, but, as you say, a bit pricey.
>>Punchline? I finally got around to >>checking the specifications on my laptop's built-in audio... and found >>that Dell dropped an STAC9205 into this D630... and that chip says it >>can deliver 24-bit samples at 192kHz. > > No, that's NOT the spec. The 192KHz is the sampling rate not the > frequency response. If you want to go up to the Shannon limit, you > theoretically can get about 80Khz for the upper frequency.
Yes. Sampling rate. To directly sample a 60kHz signal the way I was describing ( and be able to reconstruct it <grin!> ) one needs to sample faster than 120kHz. (Nyquist)
> ... You'll > need to butcher the audio amplifier section of the sound card to do > that.
Yup. That's the part I overlooked in my excitement. The ADCs I've used before were on microcontrollers, and I didn't stop to think about what kind of filtering -- with all the best intentions -- a laptop manufacturer might put ahead of an ADC "intended" for audio input, even one capable of 192ksps. Oops. My bad. <grin!> Before I read your reply I managed to get SpectrumLab installed (under Wine) and hooked up one end of a 30' microphone cable to the D630's Mic_In socket. In spite of whatever filters Dell has on its audio input, last night SpectrumLab reported two (FFT-averaged) "peaks" at 59940Hz and 60060Hz varying from 10 to 20dB above everything else. ( Right now I can barely pick out the same peaks from the surrounding "noise" (a.k.a. "Stuff I don't care about." )
> ... My guess(tm) is that's easier to add a mixer and downconvert > the 60KHz RF to a lower frequency that's more easily digested by a > sound card. That's the way DRM broadcasting is done from the 455KHz > IF frequency of a receiver. ><http://www.radiomuseum.hu/radiomuseum/rajzok/drmvevo.pdf> > With a working bandwidth of only about 5Hz, this should be easy > (famous last words).
I've got some other things I need to get done before I spend much more time on this. That will give me time to decide whether I'd rather solder up a downconverter or write code to have some microcontroller do the sampling at >120ksps for me. Decisions, decisions. <grin!> On the good side, it looks like we've finally gotten past the 2014 Groundhog's Curse. The sleet/freezing rain we got Monday and Tuesday will be replaced by sunny, high-60s weather by the weekend. Frank -- ...the fact that some geniuses were laughed at does not imply that all who are laughed at are geniuses. They laughed at Columbus, they laughed at Fulton, they laughed at the Wright Brothers. But they also laughed at Bozo the Clown. -- Carl Sagan -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney aatt mindspring ddoott com
On Wed, 19 Mar 2014 09:34:17 -0500, Frnak McKenney
<frnak@far.from.the.madding.crowd.com> wrote:

>Before I read your reply I managed to get SpectrumLab installed (under >Wine) and hooked up one end of a 30' microphone cable to the D630's >Mic_In socket. In spite of whatever filters Dell has on its audio >input, last night SpectrumLab reported two (FFT-averaged) "peaks" at >59940Hz and 60060Hz varying from 10 to 20dB above everything else. ( >Right now I can barely pick out the same peaks from the surrounding >"noise" (a.k.a. "Stuff I don't care about." )
I think you'll find that laptop internal sound cards have a rather horrible SNR (signal to noise ratio). They pickup digital hash and junk from all over the laptop. It's mostly a problem with the higher gain microphone input, but the noise can also be found on the audio output. To get rid of the junk, you should use an external USB connected sound card. I've been using cheap CM108 type USB sound dongles found on eBay for about $3 such as: <http://www.ebay.com/itm/300715727779> but there are better devices available. However, those are all usually limited to about 20KHz maximum frequency. I think a mixer to downconvert to about 12Khz will be much easier. The only problem is that if it works, the WWVB spectrum display is going to be rather dull. With only 5Hz bandwidth and very slow modulation, you're not going to see much in the way of sidebands. The only thrill will be to watch the amplitude variations. Maybe watching the other time signals might be more interesting: <http://genesisradio.com.au/VK2DX/time_signals.html>
>I've got some other things I need to get done before I spend much more >time on this.
Gee thanks. I was hoping that you would work on the problem, so I could steal the results.
>That will give me time to decide whether I'd rather >solder up a downconverter or write code to have some microcontroller >do the sampling at >120ksps for me. Decisions, decisions. <grin!>
Another possibility is to reverse engineer a sound card, and modify the audio circuitry to pass up to 88KHz. Personally, I hate programming and recommended the mixer scheme, since it has a good chance of working (and because it's my suggestions). -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
On Wed, 19 Mar 2014 09:51:18 -0700, Jeff Liebermann <jeffl@cruzio.com> wrote:
> On Wed, 19 Mar 2014 09:34:17 -0500, Frnak McKenney ><frnak@far.from.the.madding.crowd.com> wrote: > >>Before I read your reply I managed to get SpectrumLab installed (under >>Wine) and hooked up one end of a 30' microphone cable to the D630's >>Mic_In socket. In spite of whatever filters Dell has on its audio >>input, last night SpectrumLab reported two (FFT-averaged) "peaks" at >>59940Hz and 60060Hz varying from 10 to 20dB above everything else. ( >>Right now I can barely pick out the same peaks from the surrounding >>"noise" (a.k.a. "Stuff I don't care about." ) > > I think you'll find that laptop internal sound cards have a rather > horrible SNR (signal to noise ratio). They pickup digital hash and > junk from all over the laptop. It's mostly a problem with the higher > gain microphone input, but the noise can also be found on the audio > output.
You mean that a laptop manufacturer would put 192ksps/24-bit ADCs and ADCs in his equipment and then _not_ use gold-plated cables as well? Ouch. But thanks for the warning.
> ... To get rid of the junk, you should use an external USB > connected sound card. I've been using cheap CM108 type USB sound > dongles found on eBay for about $3 such as: ><http://www.ebay.com/itm/300715727779> > but there are better devices available. However, those are all > usually limited to about 20KHz maximum frequency. I think a mixer to > downconvert to about 12Khz will be much easier.
Yup. My fingers are too fat and my eyesight too poor to really hack surface-mount hardware very well.
> The only problem is that if it works, the WWVB spectrum display is > going to be rather dull. With only 5Hz bandwidth and very slow > modulation, you're not going to see much in the way of sidebands. The > only thrill will be to watch the amplitude variations. Maybe watching > the other time signals might be more interesting: ><http://genesisradio.com.au/VK2DX/time_signals.html>
Yup. I'd need a tunable LO for that (see below).
>>I've got some other things I need to get done before I spend much more >>time on this. > > Gee thanks. I was hoping that you would work on the problem, so I > could steal the results.
If I get something working I'll send you a copy of the schematic. ( Hey! Who cued Sonny and Cher on "The Twelfth of Never"??? )
>>That will give me time to decide whether I'd rather >>solder up a downconverter or write code to have some microcontroller >>do the sampling at >120ksps for me. Decisions, decisions. <grin!> > > Another possibility is to reverse engineer a sound card, and modify > the audio circuitry to pass up to 88KHz. Personally, I hate > programming and recommended the mixer scheme, since it has a good > chance of working (and because it's my suggestions).
And a very good one! <grin> I put an order in to Mouser last night for the parts to build a variant of Lyle Koehler's downconverter: A LowFER Receiver Using a "Software" IF http://www.qsl.net/k0lr/SW-RX/sw-rx.htm It uses an SA602 mixer chip, which is handy for me. My understanding of "mixing" -- of the "why" signals sometimes add and sometimes multiply -- is limited to throwing around words like "nonlinear" and "sum and difference" without necessarily being able to create one of my own. ( If I ever have my "Electron Choreographer" cards printed up -- and if I'm honest about it -- I might get away with claiming I had reached "Senior Apprentice" level. ) I'll be using a 4.000MHz crystal divided by 64 so my LO will run at 62500Hz, giving me several hours of debugging followed by -- hopefully -- 2500Hz into the laptop. Once everything works. <grin!> I have a couple of MSP430 LauchPads lying around, so later I can think about replacing the crystal/xx4060 LO with something generated under software control (think "programmable DDS"). This would let me add an LCD, buttons for adjusting the LO frequency, etc. to make a tunable VLF superhet. But that's for later. Have a good weekend. Frank -- There is something deeply fulfilling, even thrilling, in doing almost anything difficult extremely well. There is a joy and pride that come from pushing yourself to another level, or across a new frontier. A life devoted only to the present -- to feeling good in the now -- is unlikely to deliver real fulfillment. The present moment by itself is too small, too hollow. We all need a future, someting beyond and greater than our own present gratification, at which to aim or to which we feel we've contributed. -- Amy Chua, Jed Rubenfeld / The Triple Package -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney aatt mindspring ddoott com
Den torsdag den 13. marts 2014 15.51.15 UTC+1 skrev Frnak McKenney:
> I have two "atomic clocks": one is a La Crosse LCD unit, the other an > > "analog" wall clock whose hands are driven by a WWVB-sync 1xAA-powered > > mechanism. Following the recent "let's screw with everybody's clocks" > > cycle neither of my "atomic clocks" caught it, and I was reminded that > > I was Going To Fix This Problem last time. And the time before... > > <grin!> > > > > After some years I've discovered that, if I place my clocks near the > > west-most window and leave them for a few days, they will usually > > re-sync with the current WWVB time; if I don't do this it may be weeks > > or months before they pick up a strong enough signal to reset. This > > isn't a particularly onerous task, but it's only slightly less effort > > than pushing buttons in some arcane sequence to manually update a > > clock. > > > > Is there some simple way of strengthening the WWVB signal so my clocks > > will reset themselves automatically, preferably one that doesn't > > involve stringing wires to each device? > > > > The main axis of the house is a few degrees clockwise from a true E-W > > line. What I picture is an antenna near the westernmost window to > > pick up, amplify slightly (no kilowatt linears! <grin>) and and > > rebroadcast the WWVB signal directionally "down" (east) the house so > > that every device would get a stronger signal. Is there some > > commercial gadget that does this? Or would I need to roll my own? > > > > And, if I have to build it, what would be a good unidirectional LF > > antenna type? I have two neighbors to my SW and NW, and I really don't > > want to mess up their equipment. <grin!> > > > > I don't seem to be the only one with this problem, as these threads > > indicate: > > > > <http://comments.gmane.org/gmane.org.user-groups.linux.blu.hardware/589> > > <http://doityourselfchristmas.com/forums/showthread.php?11305-60-khz-Transmitter> > > <https://groups.google.com/forum/#!topic/rec.radio.broadcasting/x8WnIcRO__o> > > > > Suggestions welcome. > >
build one of these, control it from computer with NTP ;) http://www.instructables.com/id/WWVB-radio-time-signal-generator-for-ATTINY45-or-A/?ALLSTEPS -Lasse