Message-ID: <3C8F5B55.B8F16F2F@usa.net>
Date: Wed, 13 Mar 2002 14:59:49 +0100
From: "Alberto di Bene" <dibene@usa.net>
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To: "LF Mailing List" <rsgb_lf_group@blacksheep.org>
Subject: LF: Demodulator program for the W & G Pegelmesse
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Many LF enthusiasts have a Selective Level Meter, generally
made by Wandel & Golterman. Some of these units have a
demodulated output, others don't, instead providing a last
IF output at 10 kHz on the rear panel.

For this last kind of equipment I have written a sort of last IF
stage in software, which accepts as input a frequency between
40 and 20000 Hz, and extracts the AM, USB or LSB modulation
it may have, playing it through the PC sound card.

The program sports also a graphical Phase Meter, which works
only when AM is selected, and measures the incoming carrier
phase referred to the program 'BFO' phase. It can be used for
a very superfine tuning. A frequency difference of 1 Hz between
the incoming signal and the BFO produces a whole revolution
every second, so frequency differences of 10 mHz are easily
appreciated.

The program does not touch the audio mixer, so it's up to the user
to set it correctly. Basically you have to set the Recording panel
so that only Line In is selected, and the Playback panel so that
only Wave is selected. Make sure that Line In is *deselected*
for Playback.
Of course you will have to connect the 10 kHz output of your
Selective Level Meter to the Line In of the sound card.

The program has a very serious problem, as the played audio lags
the input by almost a second, so tuning is quite difficult.
This is due to the processing of the signal, and to the MME system
of Windows. There are ways to improve this, and maybe I will
pursue this, depending on my spare time and the acceptance
of the program.

Bear in mind that this is just a first cut, more an alpha version than
a beta, so do not have excessive expectations.... I wrote it more
as an exercise, using some routines I had already written for
the version 0.93 of Jason (to be released).
Of course any criticism, suggestions, bug reports are welcome.

The program can be downloaded from :
http://www.weaksignals.com/bin/radiopak_090.exe

73  Alberto  I2PHD