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: AQHURPH1nn2w3zZnskyrshKlrmOct6ThOBuAgAAMBoCAADPsFIABbwAAgAApRsQ=
Date: Thu, 6 Sep 2018 10:42:10 +0000
Message-ID: <1536230527764.58197@kuleuven.be>
References: <165a8bb827e.marcocadeddu@tin.it> <5B8F9291.7090601@posteo.de>
 <2f2c5632-b82a-91c7-3502-d88b7657d038@n1bug.com>
 <1536142926551.20983@kuleuven.be>,<7bf75bfe-2141-0589-6ffe-f2dcd86f1337@n1bug.com>
In-Reply-To: <7bf75bfe-2141-0589-6ffe-f2dcd86f1337@n1bug.com>
Accept-Language: nl-BE, en-GB, en-US
Content-Language: nl-BE
MIME-Version: 1.0
Subject: Re: R: LF: Antenna environment changes
Content-Type: text/plain; charset="iso-8859-1"
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Content-Transfer-Encoding: 8bit

Hello Paul,

getting 1 W EIRP on 137 kHz is indeed not easy for many of us.
With my 450W TX I managed to get an antennacurrent of almost 2A in winter.
My antenna was a 14m high and 25m long inverted-L with 3 parallel topload wires, estimated Rrad = 0.06 Ohm.
In theory my EIRP should have been close 700mW (taking into account the directivity of a short vertical = 3).
But I was brought back to earth by measurements and calculations done by the late PA0SE, who estimated EIRP 100mW at best, more likely 50mW.
That meanth that I would have needed 5kW TX power to het 1 W EIRP!

73, Rik  ON7YD
________________________________________
Van: owner-rsgb_lf_group@blacksheep.org <owner-rsgb_lf_group@blacksheep.org> namens N1BUG <paul@n1bug.com>
Verzonden: donderdag 6 september 2018 12:06
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: Re: R: LF: Antenna environment changes

Hi Rik,

I'm sorry you have such high losses but it is good to hear finally
that I am not the only one. I think sometimes people don't believe
me when I tell them I must run a few hundred watts on 137 kHz to
make 1 watt EIRP! It seems many are able to achieve loss around 10
to 50 ohms at 137 kHz. Hmm, not here...

Yes, we had our QSO despite some bad luck! :-) The nights which were
seriously tried for trans-Atlantic QSOs did not seem to be among the
best of propagation.

73,
Paul


On 09/05/2018 06:22 AM, Rik Strobbe wrote:
> 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