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Date: Sun, 06 Feb 2000 17:03:20 +0200
To: rsgb_lf_group@blacksheep.org
From: =?iso-8859-1?Q?V=E4in=F6_Lehtoranta?= <vaiski@dlc.fi>
Subject: LF: LF Propagation thoughts
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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
------ Tel: +358-9-4173965 ---- Fax: +358-9-4173961 ------
E-mail: vaiski@dlc.fi - alias: oh2lx@dlc.fi & oh2lx@sral.fi