LF: TECH: Loran signals received in AM as audio reference ?

[DL4YHF@aol.com]

Hello group,

I just thought about an audio frequency reference for all who don't have an
accurate audio reference but a longwave receiver (like myself..)
In one of his recent postings Jim 'BMU explained why such a reference is
required for the WOLF experiments. There MAY (!) be an easy solution to this,
maybe the experts can help to verify the following.

Here is what to do:
1.) Tune the LF RX to 100.00 kHz and set the receiver to AM (not SSB !)
    You should hear Loran's sharp "clicketiclick" sound in the receiver.
    The "clicketiclick" is a mixture of a lot of many audio frequencies,
    and because we are using an AM RX the frequencies do NOT depend
    on the accuracy of the VFO in the receiver (crude explanation...)
2.) Record a spectrogram with ARGO, SpecLab or whatever you use.
    Use a  high resolution, at least 0.01 Hz  (the attached screenshot,
    LORAN_AM.JPG, has 0.002 Hz resolution and took 6 minutes).
3.) Look at the audio frequencies close to 1kHz. There are lines visible at
       999.85 Hz
       999.96 Hz
     1000.00 Hz
     1000.13 Hz  (the strongest in the range 999 - 1001 Hz)
Note: The spectrum has been recorded in the midwestern part of DL (JO42FD),
and the amplitude of the spectra may be different in other parts of Europe
but the lines should be detectable everywhere.

I think this could be a way to verify the accuracy of ANY audio recording
tool (for the last fractions of a Hertz), no matter if a soundcard, DSP,
PIC-based converter or whatever is used.

There has been a list of Loran frequencies on this reflector a few months ago
(sh.., I didn't save it). Maybe one of the experts can calculate the accurate
frequencies contained in an AM-received Loran signal on 100kHz, or one of the
lucky fellows with a high-precision audio source can repeat the experiment
described above to check the results.

Thanks,
  73 from Wolf (DL4YHF).