to set accurate time on laptop for visual satallite tracking

Hi John
I was a bit concerned about using the ZN414 since its output is designed to deliver audio from an AM carrier, whereas the MSF signal stream looks like it will have a very low frequency AF content, perhaps forcing you to use a very large value of DC blocking capacitor at the output of the receiver. Such a large value may take some time to charge up to its normal operating bias voltage, but this would happen only when you first applied your DC power. The MSF signal (as defined at **broken link removed**) appears to be an ON-OFF AM modulation with bits defined with 100 mSec duration. So a stream of 101010 would give you a 10Hz square wave, but most of their coding will have more ones or zeroes strung together so the AF output will have content down to 1 Hz and below. So you have to couple your receiver output to a very low cutoff frequency to get the bit stream out without rounding it too much.

I have never built with the ZN414 or the MK484 so I don't even know if it is capable of demodulating to such a low AF frequency. Hopefully you have already looked at the output of your receiver on a scope and find that it is good enough. If you were interested in being quite fussy with your timing accuracy, you would want to make sure that you don't delay or slow down the edges of the waveform too much as this will add some jitter to your time signal. For example, I would want to keep these edges rising and falling in less than 5 mSec if possible to keep them crisp.

If you reconsider your choice of receiver IC you might want to look at some more complex receiver chips like Atmel/Temic U4223 to U4227, or Micro Analog Systems MAS9179 to MAS9180 series, or HKW Electronics TCR509, or UE6005. Also you could check this reference:https://www.cl.cam.ac.uk/~mgk25/lf-clocks.html
which suggest"a receiver IC for amplification, selection, AM detection and automatic gain control (e.g., Atmel T4227 40-120 kHz or U4223B 40-80 kHz, HKW UE6002/UE6005, GSG Semicon AK2124, AK2125 or AK2127, MAS MAS1016 or MAS1017)". These are all specifically designed for MSF or WWV or DCF signals and may deliver a good bit stream with much better sensitivity since they also allow use of a crystal filter.

Anyway your idea of interfacing doesn't look right to me. The receiver includes an AM detector that drives the output, so I presume there won't be much carrier signal at the output, just demodulated output (again I'm not intimately familiar with these parts having just looked at the data sheets and some examples). So, if there is no carrier, a BFO isn't appropriate, nor is a 60KHz tone decoder. Instead, you might want to consider using a tone encoder to simply shift the demodulated signal up from a very slow (10Hz) bitstream to something easier to couple into the soundcard like two tones of 600 and 800 Hz for example. In this case, you would need to have software running that does the tone decoding to detect when you are inputting a 600Hz tone vs an 800 Hz tone. However, you can avoid such complication by simply taking the receiver output, cleaning it up with a schmitt trigger and interfacing to one input bit on your parallel port. I would use that approach, and have before with a simple CW decoder that I built once.

This may work, but the next problem you may face once you get it working is that it is not very selective and so not very sensitive due to a lot of interference. However, you say that the signal is very strong at your location, so maybe you don't need to worry about this for now.

Since you have the receiver operating, can you describe the output signals?

RadioRon

Thank you Radioron for your very informative reply,and you "hit the nail on the head" the schmitt trigger was the part i was trying to think about.
I had forgotton to add that the zn414 already had a transistor stage added and the output is 2v pep so strong in fact that you can hear the 50hz mains hum modulated onto the carrier at the station.the output cap is 5uf ,as i note your concern about the low freq content of audio sig and the data stream ,as the software used on my main computor is driven directly from data output sigs of my ft847 and is delayed slightly compared to the atomic time clock sigs from the internet.
So maybe using a schmitt trigger to key the ne567 then output at 500hz is just about right to drive the soundcard ,(well i can try it anyway nothing gained nothing lost.)

This method for clocking a laptops time has to be a non serious and cheap project as the Rugby MSF clock will likely be closing down by 2007
and hopefully the loran 100khz df tx next to it ,presently the interferance from this makes the 137khz amateur band unuseable.

By then i should have a gps which would update the clock and my lat/long position directly and be living in spain where the night sky is clear more than one night a week and the time clocks arevery weak sigs there,hi.
Anyway thanks Radioron Ill let you know if it works.

Glad to help. I had a few more comments, but only on minor issues. You mentioned that you can hear the mains hum modulated onto the transmission. I'm wondering if this might not be from your own receiver/power supply. Whenever you have baseband amplification in your own device and/or are using a high impedance interface (like a signal tracer or high-z headphones), (or in those cases where you are using a superhet type of receiver you also have to avoid putting hum on your local oscillator but that doesn't apply here), you have to be careful not to amplify any of your own power supply ripple. Of course, this is easy to diagnose by operating from a dry cell, in which case you should have no power supply hum at all. When I face such problems, I like to use a differential amp or op-amp for audio amplficiation because they inherently balance out and therefore reject power supply ripple. Very handy.

I think you use the term "2V pep" incorrectly as pep means peak envelope power while 2V is simply a voltage, so I guess you meant to say peak-to-peak or just peak. I agree that 2Vpp is a nice strong signal.

Sounds like you are choosing to square up the receiver output, then key a tone encoder which then feeds the sound card. That should work OK, and we look forward to hearing of your progress.

regards

Yes thanks RadioRon
the rx works well and is driving the soundcard ok, but even after allowing
15 mins to sync ,the time signal is 1min 45 seconds different to the atomic clock via internet on my main computor,using the program i had planned to use( then i noted i would have had to pay to register it to update the laptop rtc clock!)
Fortunatly i also had a program called spectrum analyser by DL4YHF net
this was aimed at low freq rf exploraton (soundcard drive 0-22khz) not much use on the laptop while on its switich mode psu( very dirty) but ok
out in the fields.
Well this program includes a radio timeclock decoder and after allowing for hour sync reset is within 0.5 sec of the main computor and then auto resets my laptop clock, next ill need to change the laptops rtc battery
as after a day or so without the rx connected it loses time
now i just need the clear sky night ,ha
bye for now RadioRon and thanks again.