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.
150th harmonic of F1 at 6.667555674 is 1000.133351Hz
140th harmonic of F3 is 999.8571633 Hz
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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