[time-nuts] Receiving the MSF time signal on cheap radio modules

[Bob kb8tq]

Hi

> On Feb 6, 2018, at 4:19 PM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
> 
> --------
> In message <CAGJ4F+54Sxqc34fpNefNW3q3emHmq+uC-V-Lfc5Bnfk7h7qWUw at mail.gmail.com>, "Deirdre O'Byrne" writes:
> 
>> With a blame algorithm in place it should be possible to recover these signals.
> 
> Yes, easily.
> 
> At distance MSF is significantly harder to receive than DCF77.
> 
> One of the reasons is that USA also operates two 60kHz transmitters
> also very precisely on frequency, so there are areas of the world
> where the three signals cancel and areas where they reinforce
> each other.

I believe we only have one transmitter on the air at 60 KHz in the US. The 
Japanese do indeed operate multiple transmitters on the same frequency 
( 40 KHz). There have been a number of proposals to set up a second US
transmitter. The last time I noticed them beating the drum for one, it was 
going to be at 40 KHz rather than 60 KHz. The proposal pretty much died 
yet again ….

Since MSF *is* on 60 KHz, you do indeed get dead spots. There probably is an
interesting plot of locations that have issues with both the 40 KHz and 60 KHz
transmissions due to simply being in the wrong place. 

Bob

> 
> I tried to model this many years ago, but I don't trust the result,
> somebody with better HF-propagation chops than me should look at it.
> 
> In addition to that problem, switch-mode designers seems to just
> *love* 60 kHz, and at least here in Denmark there is a lot more
> "hash" around 60 kHz than 77.5 kHz.
> 
> Finally, the modulation scheme of MSF is a bit on the overengineered
> side, which makes pulse discrimination needlessly hard - as you have
> also found out.
> 
> The big advantage of the blame algorithm is that since it is so
> tolerant of missing pulses, you can be throw everything away which
> isn't 100% clearcut.
> 
> If you look at the top of the dcf77.c file, you can see how I did
> that for DCF77, but the complex modulation of MSF needs a much
> more complex state engine there.
> 
> Finally, many of the small "clock-receivers", like the one you use,
> are optimised for battery-life and therefore they use very resonant
> filters, often crystal-filters, and heavy low-pass after demodulation,
> and that trows away a LOT of information which would be useful to
> have to discriminate the pulses.
> 
> If you go for the SDR approach, you will have much more information
> available, and can use much more well-behaved filters to detect the
> pulses, and one added advantage of carrier-tracking is that the
> power-modulation is carrier-synchronous, which makes them much
> easier to spot.
> 
> So really:  Get yourself an 1MSPS ADC chip and go that route instead.
> 
> (In theory, certain modern sound-cards should be usable for this if
> you can rip out their low-pass filters.  Havn't tried.)
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.
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