Dear Markus, Lawrence and others,
Thanks for your interesting comments on this theme.
> The slow phasing effect is caused by pulsegroups of these very similar rates,
> walking through one another in time.
I think I can hear two effects which might be described as phasing.
One is due to the different GRIs (Group Repetition Intervals, i.e. pulse group
rates) which Markus describes. This appears a a change in the chittering sound.
When the groups coincide you hear it as "chit chit chit" and the pulsiness
is more pronounced: you can hear this about 1/5 to 1/4 of the way through the
recording. When they fit in each others' gaps you hear "chitchitchit" and the
sound seems smoother: you can hear this just before half way through the
recording.
The other effect is a change in the relative strengths of higher and lower
audio frequencies. You can hear this from about 4/5 of the way through to
nearly the end, where the sound cycles between treble and bass. Presumably this
is cancellation in some part of the 90-110 kHz spectrum, though the treble will
be represented by both the parts just above 90kHz and those just below 110 kHz,
so presumably it is subtler than that*. Maybe this is caused by
frequency-selective fading, presumably what Lawrence described as the "musical
sounds they made as sky waves did their thing". Could someone more knowledgable
than me comment on that?
* Unless Lawrence was demodulating as SSB, in which case he would see only one
half of the spectrum.
For those who have deleted the original message, the recording is at
> http://kl1x.com/loranalaska.wav
73,
Chris G4OKW
-----------------------
Dr Chris Trayner
School of Electronic & Electrical Engineering,
The University of Leeds,
Leeds LS2 9JT, United Kingdom
Tel: +44 113 34 32053
Fax: +44 113 34 32032
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