From: "Hans-Joachim Brandt" <hajo.brandt.dj1zb@t-online.de>
To: rsgb_lf_group@blacksheep.org
References: <12FesM-0Y9MaOC@fwd07.sul.t-online.de> <3.0.6.32.20000202093713.0084b7c0@laatikko.saunalahti.fi>
Subject: Re:  LF: Change of ground resistance due to frozen ground
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Date: Wed, 2 Feb 2000 14:39:07 +0100
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Dear all,

when collecting reports about changing ground resistance changes due to frozen 
ground (and the ground covered with snow) I think we must take into account the 
following difference:

Commercial stations with a well elaborated ground system may not notice this 
effect as much as radio amateurs who have limited possibilities to install 
effetive ground systems.

At present I am just using my house ground for LF. I have noticed the difference 
in the antenna match (up to S = 2), I have measured the direction of the change, 
I will repeat these measurements in the next winter season, and I will install 
something to be able to re-match to this change.

All other observations, preferably from other radio amateurs, however, are 
welcome.

73 Ha-Jo, DJ1ZB  


Vaeinoe Lehtoranta schrieb:
> In Finland we have some experience with frost.
> Information about its effects on ground wave
> propagation is not very well established.
> Same with TV & FM space wave (I am not talking
> about frost on antennas). What effect frost can
> have on higher angle sky wave component on
> LF, MF or even HF frequencies, I just wonder...
>
> I do have some frost depth statistics from
> Southern Finland and have tried to find some
> correlation between measured LF/MF ground wave
> values and frost. The stations both flight and
> and ground (fixed qth) measured consist of:
>
> - One LF BC station, Lahti 254/252 kHz, 200 kW,
> - Several MF BC stations, two still active,
> - More than 100 MF aviation beacons (NDB & L),
> - A total of some 10 maritime MF DGPS beacons.
>
> YLE measurements began in the 1950's but only
> VHF/UHF will continue after 1st Jan 2000. Private
> LF measurements continue from my poor qth...
>
> Finnish NDB's and locators (LO/LI) presently use
> either 11 m or 14 m high top loaded monopoles.
>
> Finnish DGPS beacons use a 36 m high top loaded.
>
> Locator with a 14 m high monopole and 500 W out
> radites between 5 and 10 W EMRP (1% to 2%).
>
> DGPS with a 36 m monopole and 100 W out radiates
> approximately 5 W EMRP (5%), or even more.
>
> Raimo, OH2MRX is real aviation beacon expert
> and he reads these messages. He and other CAA
> fellows may confirm whether frost plays some
> significant role on NDB/L behaviour.
>
> According to our experiences, as propagation
> researches something happens in beacons close
> environment when the water content changes
> from liquid to solid or vice versa.
> >From long time ground wave measurements we can
> easily see that the most significant variable
> to effect indicated F-s values is air temperature.
> This was documented already in the 1940-1950's.
> Earth net efficiency varies from case to case.
>
> 73 de Vaino, OH2LX
>
>
>
>
> At 19:20 2.2.2000 +1300, you wrote:
> >Hans-Joachim Brandt wrote:
> >
> >> Besides just noting the change It would have been interesting, of
> course, to
> >> find out into what direction the ground resistance has changed. On one
> of the
> >> last cold days and before the snow had disappeared I checked it with a
> resistive
> >> bridge to find that the total feed point resistance of my antenna (when
> tuned to
> >> resonance) had decreased from 100 ohms down to 60 ohms!!!
> >
> >I do not have a reference at hand to quote a definitive response, but my
> >recollection of ground parameter data is that frozen ground is "bad
> >news" for ground wave loss, as is fresh water.  Your measured result is
> >the other way round.  I will try to find a text book reference on frozen
> >ground losses versus unfrozen.
> >
> >By the way, the temperate climate here in Wellington, New Zealand
> >involves a few frosts in the winter but no frozen ground as such, so I
> >have not experienced the type of conditions that Hans-Joachim is more
> >familiar with.
> >
> >73, Bob ZL2CA
>
> ----------------------------------------------------------
> 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
>