[ntp:questions] Only Garbage from Raw DCF

Frantisek.Rysanek at post.cz Frantisek.Rysanek at post.cz
Tue May 30 08:13:13 UTC 2017


> It looks like you still have some missing pulses, probably due to local
> interference.   This is a problem here as well, as you saw from my logfile
> posting. 

This thread is pretty old, so just for the record:

Note that there's a relatively easy way to judge the quality of DCF77 reception: using your ears :-) The regular pulses are extremely easy to distinguish from any kind of "noise", which presents itself as random "warbling". If all you can hear is the "alien scanner tapping", you've found a nice spot for your antenna.

To get your alien scanner going, just plug or "wiretap" the output pulse train of your DCF77 receiver into a speaker. The output itself is too "soft" to drive a passive speaker or earphones, but if you use a powered computer speaker (anything you find lying around), that will have a high-Z line input and will work. Or, you can plug the DCF77 pulse train into the line input of a computer sound card. Note: line in, not microphone in - the signal is too strong for a mic in. I've used this not only for immediate playback, but also for recording. This way I was able to discover ionospheric interferential outages in my reception. Obviously you don't want to sit there listening to hours of DCF77 tapping, but you can use software such as the Spectrum Lab to create an FFT waterfall, which will fit the spectrum of the "audio" for the period of a day onto a single screen of the waterfall diagram.

Example spectrum waterfall:
http://support.fccps.cz/download/Meinberg/prehled/2012_06_29__around_23-00_UTC_spectrum.png

Using some additional circuitry, I was also able to measure the RSSI signal from a Meinberg analog receiver:
http://support.fccps.cz/download/Meinberg/prehled/RSSI_UL.png

DCF77 is analog HAM fun, especially if you live further away from Frankfurt (a couple hundred km). YMMV.

Frank



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