From: Rik Strobbe <rik.strobbe@kuleuven.be>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Thread-Topic: R: LF: Antenna environment changes
Thread-Index: AQHURPH1nn2w3zZnskyrshKlrmOct6ThOBuAgAAMBoCAADPsFA==
Date: Wed, 5 Sep 2018 10:22:08 +0000
Message-ID: <1536142926551.20983@kuleuven.be>
References: <165a8bb827e.marcocadeddu@tin.it>
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Hi Paul,

same here, losses are high in summer: up to 70 Ohm (475 kHz) or 180 Ohm (137 kHz). In winter it drops to 35 Ohm (475 kHz) and 120 Ohm (137kHz).
I always assumed it was not so much affected the soil but rather by all the trees surrounding the antenna that loose their leaves and go to "sleep" in winter.
Last february I raised the antenna from 12m to 14m in my attempt to get some extra ERP to cross the Atlantic and actually the losses increased slightly. I thought this was caused by the topload coming closer to some branches. But fortunately the overall effect was positive and we had our QSO ;-)

73, Rik  ON7YD - OR7T

________________________________________
Van: owner-rsgb_lf_group@blacksheep.org <owner-rsgb_lf_group@blacksheep.org> namens N1BUG <paul@n1bug.com>
Verzonden: woensdag 5 september 2018 11:06
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: Re: R: LF: Antenna environment changes

Marco,

... a wingbeat of a butterfly... is very descriptive. I like it. :)
Maybe with a sensitive detector I can use the LF antenna to count
birds flying under it. :)

Stefan,

I have not seen any significant change in loss resistance during the
summer. Rain, dry... hot, less hot... grass mowed or not mowed seem
to have not much influence. My loss resistance in summer is very
high. I need that aluminum foil!

During the winter my loss resistance changed a lot with temperature.
Colder = lower resistance. I did not understand what was changing. I
do not think variations in temperature could affect the ground very
much with 1m of snow over it but maybe I am wrong. Perhaps it was
the snow itself changing with temperature, or maybe it was the
nearby trees.

73,
Paul


On 09/05/2018 04:23 AM, DK7FC wrote:
> Paul,
>
> did the LF loss resistance drop after mowing the grass?
> Someone should try to roll out household aluminium foil completely
> within a radius of the height of the antenna to see how it loweres the
> losses :-) Not so expensive actually.
>
> 73, Stefan
>
> Am 05.09.2018 09:56, schrieb marcocadeddu@tin.it:
>> .. a wingbeat of a butterfly..
>>
>> be careful to move around the antenna and touch metal parts while
>> transmitting Paul it is a very "reactive" area not only for the field
>> strenght concept :-))
>> I guess that the pipe laying on the ground it is part of the ground
>> itself (maybe improving it ) when you rise it from ground level and
>> eventually connect to other existing metal parts you really make
>> change in the environment of the antenna (it is like to tophat wires
>> moving in the space when wind blows)
>>
>> 73, Marco IK1HSS
>>
>> ----Messaggio originale----
>> Da: paul@n1bug.com
>> Data: 5-set-2018 1.09
>> A: "rsgb_lf_group@blacksheep.org"<rsgb_lf_group@blacksheep.org>,
>> "rsgb_lf_group@yahoogroups.co.uk"<rsgb_lf_group@yahoogroups.co.uk>,
>> "Discussion of the Lowfer (US, European, & UK) and MedFer
>> bands"<lowfer@mailman.qth.net>
>> Ogg: LF: Antenna environment changes
>>
>> Subtitle: Be careful what you do in the vicinity of your LF antennas...
>>
>> I had a 14m length of aluminum tube (proposed 30 meter rotatable
>> dipole) laying on the ground just under one end of the top hat of
>> the LF antenna. Today I picked it up and moved it about 20 meters
>> away. To get it off the ground for mowing, I ran it through the
>> lattice of a short tower (9m) that is not at all under the LF top
>> hat. I placed it about 2m above ground. This caused the LF antenna
>> resonance to change so much I could not retune with the variometer!
>> It was quite a large shift in resonant frequency.
>>
>> I then experimented with moving the piece of aluminum tube around.
>> It seems I can lay it on the ground anywhere I want with no affect
>> to the LF antenna. But put it one or two meters above ground
>> connected to another tower or mast and the LF antenna is drastically
>> changed.
>>
>> I must remember not to move any pieces of metal around while the
>> beacon is active! :-)
>>
>> Paul