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