LF Propagation thoughts
Sun, 06 Feb 2000 11:49:30 -0500
Väinö Lehtoranta wrote:
> Some thoughts on 136 kHz Ionospheric propagation
> Sorry for this not being in phase with T/A ideas.
> I have found exploring LF propagation refreshing
> - after a 20-25 year sleepy period. In fact some
> of my superiors asked me to stop LF/MF research
> sometime during the last part of 1970's...
> Succeeded in keeping 24h LF/MF recordings going
> on until the end of 1999; only VHF/UHF continues.
> The biggest surprise has been the intensity of
> the ICM (Ionospheric Cross Modulation) audios on
> Burg 138.83 kHz carrier. Reaction can be partly
> explained by the lack of "normal" interferers.
> Sometimes I can follow Kaliningrad 1386 kHz
> program by listening it riding on Burg carrier.
> They are supposed to run >1000 kW to a Dir.ant.
> Signal strength variation on short paths
> There (still) is a lot of moderately fast signal
> strength variation on short LF paths compared to
> longer paths. Burg 138.83 kHz Fs varies much more
> than Mainflingen 128.93 kHz signal. The morning
> "dip" appears mainly on longer 128.93 kHz path.
> It is normally said in literature that the LF
> reflection height changes from about 72 km
> near noon to about 90 km at night. BUT: over
> distancies less than about 300 km, LF waves are
> reflected near 80-85 km near noon and about
> 90-100 km at night. So, for natural reasons there
> appears to be more fading on short paths compared
> to longer paths. At our latitudes, even in
> Southern Finland, there is a lot of ionospheric
> propagation on LF during daytime in winter.
> Eg today I heard SXV 135.8 weakly all day long.
> We have one report on a 92 km long path (Lahti).
> On the practicability of talking about "hops"
> Suggested experiment: Draw a circle with a radius
> of 63.70 cm. Then draw a slightly bigger circle
> with radius of 64.50 cm, using same center point.
> With a reflection height of some 80 to 90 km the
> space between the concentric circles is small..?
> Pictures are 99% drawn to a completely wrong scale.
> Might be better talk abt "bends" instead of "hops".
> Not all active hams are interested on this kind
> of digging into propagation details. For those who
> are, I'll be glad to calculate selected paths etc.
> 73 de Vaino, OH2LX
> PS As an IARU Region 1 Auroral studies coordinator
> I should spend more time with Aurora Borealis...
> On clear evenings I do watch the Northern sky...
> V.K.Lehtoranta, OH2LX, POBox 50, FIN-05401 Jokela, Finland
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