An AM detector will recover the envelope of each of the chains passing
through the receiver, and generate audio lines at harmonics of each of
the four repetition frequencies.   Here are the frequencies I have in a
Loran interference prog written some time ago, perhaps someone can
confirm these are fully valid.

There will be other intermodulation products as well, but I can't be
bothered calculating them :-(
Such as 70 * F3 + 75 * F1 = 999.9952572 (just one of an almost infinite
number of products)

Can't see where a line at exactly 1000 Hz comes from, but it may fall
out of the IM product calculations eventually

f1 = 100000 / 14998       '(74990us / 5)
f2 = 100000 / 13462     '(67310us / 5)
f3 = 100000 / 14002     '(70010us / 5)
f4 = 100000 / 18014     '(90070us / 5)


Andy  G4JNT

-----Original Message-----
From: [email protected] [mailto:[email protected]]
Sent: 2001-04-25 14:41
To: [email protected]
Subject: Re: LF: Calibration and Loran lines


Alberto di Bene schrieb:
> A couple of months ago, someone, don't remember who,
> posted a message describing a method for frequency
> calibration that relied on receiving the Loran signals
> with the RX set to AM mode.
>

> Unfortunately I am unable to retrieve that message, > probably I have inadvertently deleted it.

> Could please somebody send it to me again, TNX.
>
> 73  Alberto  I2PHD
>
Hi Alberto,
de dj8wx/Uwe
I guess it has been Wolf.
His mail datet 20.03.01:

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).

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