Date: Sun, 31 Dec 2000 01:51:28 -0500
From: "'Geri' Kinzel, DK8KW" <DK8KW@compuserve.com>
Subject: LF: Slow Voice Experiments
To: rsgb_lf_group@blacksheep.org
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Hello LF Enthusuasts,

after Markus' succesful one-way slow-voice transmission on LF we will try
to conduct a two-way QSO in this mode today. 


I will use the follosing parameters:

The audio frequency range between 300 Hz and 2300 Hz is reduced in speed by
8 times. The transmission spectrum after the conversion will be transmitted
between 137.350 kHz and 137.600 kHz USB (250 Hz wide, so a narrow CW-filter
can be used), so that 137.350 kHz corresponds to the 300 Hz audio frequency
and 137.600 kHz corresponds to 2300 Hz audio. 


For demodulation with an audio mixing software (e.g. Cool Edit, Goldwave,
etc.) two steps are necessary: first, the recording has to be speeded up by
8 times to re-gain the original audio bandwidth, second the audio signal
has to be shifted by a certain fixed frequency to get the audio passband
back to the original position. This can be done for example in Cool Edit
using the "generate", "tone" menue and the "modulate" option, which
simulates a ring modulator mixing with the generated frequency. After the
ring modulation two sidebands are generated, so that one needs to be
filtered out.

Walter, DJ2LF, has successfully used another method to shift the audio
frequency. He fed the audio signal into an SSB transceiver and could change
the pitch by changing the receive frequency.


Markus and I will meet today, Sunday, December 31st, 2000 at 09.00 UTC on
137.500 kHz in PSK31 to arrange the voice transmissions. In between the
voice transmissions we will use CW on 137.475 kHz top arrange beginning and
ending of the voice transmissions. In between the transmissions there will
be a gap in which we will try to demodulate (and understand  -hi-) the
transmitted signal.


If you hear any spurious signals outside of the announced band (137.350 to
137.600 kHz), please let me know. I am using a 135.500 kHz exciter signal
fed by an audio frequency signal between 1850 and 2100 Hz to generate the
LF signal and I will try to keep my transmission as clean as possible. 

Best 73

Geri, DK8KW (W1KW)