[Fwd: LF: Slow Voice Experiments]

[Andre' Kesteloot]

"'Geri' Kinzel, DK8KW" wrote:

> 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)