From: Chris Trayner <C.Trayner@leeds.ac.uk>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Date: Sat, 20 Feb 2010 11:21:05 +0000
Thread-Topic: LF: Loran A and C
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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 chitt=
ering 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. Presumabl=
y 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 som=
eone 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